AM vs FM
Fran & Chris
started again with money tight he bought the Hitec 3 channel AM radio.
Now the guys at my club say that they would like him to get an FM set.
Whats the big deal? Is AM really that bad?
Cregger
collection and to let him know how much of their money they want him to
spend on the new FM set.
All radios on the market today (sold new in the USA) comply with the FCC's
current type acceptance and AMA requirements. There is nothing worse than
non technical types trying to foist their ignorance upon the unsuspecting.
Tell your Dad welcome back on our behalf.
Ed Cregger
ecre...@mindspring.com
Fran & Chris <bus...@ix.netcom.com> wrote in message
news:3834C60F...@ix.netcom.com...
Jim
fine..no problem. Your Dad's club is misinformed!
Cregger wrote in message <812mo6$82i$1...@nntp9.atl.mindspring.net>...
mkir...@rochester.rr.com
Fran & Chris <bus...@ix.netcom.com> wrote:
> Dad just got back into flying after 40+ years absence. In getting
> started again with money tight he bought the Hitec 3 channel AM radio.
> Now the guys at my club say that they would like him to get an FM set.
> Whats the big deal? Is AM really that bad?
With "money tight" he could've gotten a lot better deal than one of
those Hitec Focus III units. They're like $80-$90 right? Yet you don't
get batteries or a charger. That'll set you back $30, more if you get a
"good" charger. Forget using Alkalines; use 'em for a day, chuck 'em,
and spend another $8-$10 on a 12-pack at Wal Mart??? No way!
He could've gotten a 4-channel Hitec Focus 4 from Hobby Horse, or a
4-channel Tower System 3000 from Tower with servos and NiCds for $130,
and he would've had everything he needed, including an aileron channel.
While FM gives you clearer signals and longer range with slightly less
sensitivity to outside interference, there is really nothing "WRONG"
with AM. It makes the plane go 'round, right? As long as you're not
violating the rules at the field who cares what modulation you use? You
can still buy AM radios, generally with 4 channels or less. The problem
is you have to look to find them. FM has the overwhelming majority of
the market right now, like 99.999999999% if I were to hazard a guess.
Sent via Deja.com http://www.deja.com/
Before you buy.
unowho
Don
hear the guys at our field talking about the unreliability of AM systems.
This is usually going on while 3 to 4 at a time are trying to buy my system.
Stay with what you have.
Fran & Chris wrote in message <3834C60F...@ix.netcom.com>...
Spadman
> started again with money tight he bought the Hitec 3 channel AM radio.
> Now the guys at my club say that they would like him to get an FM set.
> Whats the big deal? Is AM really that bad?
Tell your Dad "welcome back". In the long run the decision to buy the Hitec
may not have been as prudent or economical as he thinks. However there is
absolutely nothing wrong with a modern AM rig. I have one in one of my
gliders and have had less problem with it than some of my more expensive
radios. (I can't program the VCR yet!). I think the respnse to your father's
radio was borne out of old ideas thet AM was broadband and may interfere with
others, and in fact it was the recievers that were broad. It is also
slightly more prone to outside noise but only slightly, and the newer radios
like the Hitec are very narrow. They have to be, to meet regulations. I
personnaly might have a problem flying next to a old AM but certainly not
your Dad's. Tell his friends to get a grip and lighten up. If he showed up
at our field he would be welcome. -- Spadman from Canada's Eastern Coast
Brokebob
channels than FM. It could use slightly more transmit battery energy than FM
but all that takes is a glance at the meter now and then.
brokebob
Halsmith56
Paul Mcintosh
congested urban areas, especially close to busy freeways. I found this
out when I had problems with an electric powered sailplane in Whittier
Narrows Park. I called them for some info and they told me about some
higher powered mobile phones (NOT cell phones) that cause the AM systems
a lot of trouble. My rudder would periodically go full left for a
second or two and the motor would surge.
Cregger wrote:
>
> Tell your Dad to tell the guys that want him to fly FM to take up a
> collection and to let him know how much of their money they want him to
> spend on the new FM set.
>
> All radios on the market today (sold new in the USA) comply with the FCC's
> current type acceptance and AMA requirements. There is nothing worse than
> non technical types trying to foist their ignorance upon the unsuspecting.
>
> Tell your Dad welcome back on our behalf.
>
> Ed Cregger
> ecre...@mindspring.com
>
> Fran & Chris <bus...@ix.netcom.com> wrote in message
> news:3834C60F...@ix.netcom.com...
Cregger
difficult time. FM is more prone to multipath problems than AM. All you have
to do to trick it up is put it near a lot of refelctive material about two
meters long to learn what I am talking about (72MHz).
The problem you are referring to has more to do with how many stages of IF
are used in the receiver, not whether it is AM or FM.
I get livid when someone owns equipment and is told it is not suitable
because it is not FM, PCM or whatever, by those who do not have a clue as to
what they are talking about. (Not you, Paul).
If the members railing against his father's AM set had specifically stated
the radio manufacturer and the model type, then I would listen to them and
give their comments due consideration. But a blanket indictment of AM, if
that is what truly transpired, is ignorance at its worst.
Ed Cregger
ecre...@mindspring.com
Paul Mcintosh <war...@dancris.com> wrote in message
news:3835BB00...@dancris.com...
Don Hatten
RITCH GUY9 wrote:
> It is very nessary to buy an fm radio it is mutch less lickley to have
> interfeareance
A.T.
are sold than FM. A number of multi channel RC sets are regularily used
at our field on AM with no adverse effect on any FM set etc.
Check out all the RC Car and Boat sets. Futaba Electric flight sets were
all AM including those great little 4MNCR RX/ESC units. Many of those
units are also used to fly gliders/slopees etc. Power Flyers are in the
minority of recreational RC users.
AM has a longer range than FM and will penetrate obstacles better.
Verify by driving accross country and your FM radio station will cut out
in 2/3 the distance of your AM set.(or risk your good RX to vibration
damage and place in a hot gas car - pull the throttle and seee how far
it will go before "Hey, I ain't got it" then do the same with AM which
excepting any interference (usually well past the FM range) will keep
going further. (FM often hides/cloakes some local interference until to
late and you fly into that dreaded hot spot and Wham)
regards
Alan T.
mkir...@rochester.rr.com wrote:
>
> In article <3834C60F...@ix.netcom.com>,
> Fran & Chris <bus...@ix.netcom.com> wrote:
> > Dad just got back into flying after 40+ years absence. In getting
> > started again with money tight he bought the Hitec 3 channel AM radio.
> > Now the guys at my club say that they would like him to get an FM set.
> > Whats the big deal? Is AM really that bad?
>
> With "money tight" he could've gotten a lot better deal than one of
> those Hitec Focus III units. They're like $80-$90 right? Yet you don't
> get batteries or a charger. That'll set you back $30, more if you get a
> "good" charger. Forget using Alkalines; use 'em for a day, chuck 'em,
> and spend another $8-$10 on a 12-pack at Wal Mart??? No way!
>
> He could've gotten a 4-channel Hitec Focus 4 from Hobby Horse, or a
> 4-channel Tower System 3000 from Tower with servos and NiCds for $130,
> and he would've had everything he needed, including an aileron channel.
>
> While FM gives you clearer signals and longer range with slightly less
> sensitivity to outside interference, there is really nothing "WRONG"
> with AM. It makes the plane go 'round, right? As long as you're not
> violating the rules at the field who cares what modulation you use? You
> can still buy AM radios, generally with 4 channels or less. The problem
> is you have to look to find them. FM has the overwhelming majority of
> the market right now, like 99.999999999% if I were to hazard a guess.
>
Jim White
>Sorry, but not all will agree with your 99.99+%...Many Many more AM sets
>are sold than FM. A number of multi channel RC sets are regularily used
>at our field on AM with no adverse effect on any FM set etc.
>Check out all the RC Car and Boat sets. Futaba Electric flight sets were
>all AM including those great little 4MNCR RX/ESC units. Many of those
>units are also used to fly gliders/slopees etc. Power Flyers are in the
>minority of recreational RC users.
fair info.....
>AM has a longer range than FM and will penetrate obstacles better.
>Verify by driving accross country and your FM radio station will cut out
>in 2/3 the distance of your AM set.(or risk your good RX to vibration
>damage and place in a hot gas car - pull the throttle and seee how far
>it will go before "Hey, I ain't got it" then do the same with AM which
>excepting any interference (usually well past the FM range) will keep
>going further. (FM often hides/cloakes some local interference until to
>late and you fly into that dreaded hot spot and Wham)
bad info.... you're extrapolating broadcast band experience to RC...
not applicable.... in broadcast bands you're comparing 540 to 1600 khz
AM to 88-108 mHz fm.... there IS no comparison.... in RC use, both
operate line of site on the same frequencies with the same radiated
power and the same recievers and antennaes... soooooo.... the
differences, as noted, are very minute.... truth be known the REAL
reason for using FM is the availability of those chips developed for
all of the commercial FM applications... they make reciever design an
excercise in adapting the manufacturers data sheet suggested
designs... money saved is money made...
Jim White
AMA 2466
WB2WOY
WPMPA/BCF/PFC
SouthShoreSoftware
Treasure Island, FL
Jim White
>AM is just fine. It will not cause more or less interference to nearby
>channels than FM.
good info.....
>It could use slightly more transmit battery energy than FM
>but all that takes is a glance at the meter now and then.
bad info.....
>brokebob
RITCH GUY9
Mike Dumas
Cregger wrote:
> We can find an environment in which virtually any radio will have a
> difficult time. FM is more prone to multipath problems than AM. All you have
> to do to trick it up is put it near a lot of refelctive material about two
> meters long to learn what I am talking about (72MHz).
Well I've only been a FCC licensed Commercial Radio Technician since 76,
First Phone and then PG class license... So i admit i don't know everything.
But multipath is not dependent upon the form of modulation that you use,
as in AM vs FM. Ever see more than one picture on a TV when rotating
its directional antenna? That's multipath, and the video picture is AM,
(and usually around the 72mhz band) where the sound is on a FM sub carrier.
And Ed, how many times have you flown with the planes antenna or the TX
surrounded by 2 meter long wires, rods, tubes... to act as reflectors?
Just like you started above, "We can find an environment in which virtually
any radio will have a difficult time."
And this is one of them,
and its not dependent on AM or FM but the frequency...
Different frequency bands have different characteristics.
If you disagree then you start flying on 27mhz AM in a big city next to
a busy interstate full of truckers using over modulation and illegal amps
on their rigs, and tell us how much better AM is than FM. ;)
If AM is so much better why did the R/C industry upgrade to FM
AND why aren't any PCM radios offered on AM?
Would you pay $1500 for a high end AM Futaba radio???
A Lightening Strike 2 states away can cause a Static Crash on a AM radio
BUT not on a FM radio.
Commercial radios in the VHF Low (well below 72mhz.) thru Microwave
(well above 72mhz.) bands including Cell Phones upgraded to/use
FM for a reason, less inherent noise problems under all conditions.
> The problem you are referring to has more to do with how many stages of IF
> are used in the receiver, not whether it is AM or FM.
Actually more like Single or Dual Conversion and the type and bandwidth of
filtering used. Compared to these the # of IF stages is of minor importance.
Add a helical resonator to the RX if you really want to cut interference.
Interference thru the Antenna that is. Put the RX in a metal shielded case
for stronger signals, like Proline did in the 70's!
Old Proline dual conversion, well shielded RXs had much less problems with
interference than the Futaba... single conversion RXs did!
Jim Fosgate knew how to build his radios!
I'm not as familiar with Kraft, they may have used dual conversion too.
> I get livid when someone owns equipment and is told it is not suitable
> because it is not FM, PCM or whatever, by those who do not have a clue as to
> what they are talking about. (Not you, Paul).
Actually I agree, in most places AM is good enough...
But I keep uncontrolled emotions out of it. ;)
In radio congested areas, FM gets the Big Nod.
mike
Hey, I'm only a trained and experienced professional, what do I know? ;)
Mike Dumas
Jim White wrote:
> bad info.... you're extrapolating broadcast band experience to RC...
> not applicable.... in broadcast bands you're comparing 540 to 1600 khz
> AM to 88-108 mHz fm.... there IS no comparison....
Exactly, the LF broadcast band has totally different propagation
characteristics
than the VHF band does. Just as VLF can talk to Subs in the ocean...
VHF gets attenuated by foliage (tree leafs...), and everybody knows that
a couple hundred miles of water is denser than the same in foliage.
> ... truth be known the REAL
> reason for using FM is the availability of those chips developed for
> all of the commercial FM applications... they make reciever design an
> excercise in adapting the manufacturers data sheet suggested
> designs... money saved is money made...
Now Your copping out to preconceived ideas Jim!
Its easier and cheaper to build an AM RX and TX, the means of modulation
and detection are much simpler... Like an old crystal radio for RX...
Its a diode, a capacitor, a coil of wire and an earpiece, that's all you need
to make an AM RX!
FM, OTOH, takes complex detectors to RX the signal!
The real reason FM is preferred is noise, static, immunity!
And line of sight (LOS) thinking of VHF doesn't enter into it, when a plane
is flying its LOS is much greater than yours on the ground, so static or noise
immunity is a real problem!
BUT for cars, boats (as others try to rationalize)... its NOT!
AM is plenty good, being on the ground, with the same power TX and a
shorter LOS AND a much shorter required range, the TX signal is strong
enough to overwhelm the static/interferance problems!
mike
But then I only do Radios, Radar's, Satellite Comm systems...
for a living, what do I know??? ;)
Cregger
paper from the FCC. Mine even includes a radar endorsement - big deal. Its
possession hardly makes me, or anyone else, a trained professional. I hope
you are relying on more credentials than that for your stated
professionalism.
I don't claim to be a radio expert and I certainly never claimed that AM was
superior to FM. Where did that come from?
FM is not clearly superior to AM. It is different, with characteristics that
are useful under certain circumstances. The same can be said for AM, as is
currently being used for air traffic control on certain frequencies. But
before this goes any further, our R/C systems do not use AM or FM in the
business/ham/CB/broadcast sense, so the arguments are moot anyway.
I'm going to stop right here as I suddenly remembered a few conversations
that we had a while back.
Ed Cregger
ecre...@mindspring.com
Mike Dumas <mi...@vci.net> wrote in message news:38363A76...@vci.net...
VWhed84
ATV transmitter in my plane for video. I read somewhere that they recommend
shielding the reciever. What would be the best way to do this? Steel, copper,
aluminum? Also, would the shielding have to ground to anything? Any help
appreciated, thanks, derek.
Little gold car 1985 Toyota Tercel
263,000 miles and counting.
Visit a cool tercel page
http://www.geocities.com/MotorCity/Garage/4989/4x4tercel.htm
Jim Archer
receivers in aluminium cooking foil. Their theory is that it helps block
potential interference from a nearby T.V. transmitter. No comment.
Regards
Jim Archer
52o38' North
1o 15' East
VWhed84 <vwh...@aol.com> wrote in message
news:19991120110518...@ng-cr1.aol.com...
Cregger
Included in some of their documentation (upon request) is a paper outlining
shielding considerations for R/C receivers when operated in a heavy RF
environment, such as that created when an ATV 70cm Tx is onboard a model
aircraft.
There is more to it than simply enclosing the R/C receiver in a shielded
case. There is also the incorporation of a low pass filter INSIDE the metal
shielded enclosure that is connected to the antenna.
I have dealt with PC Electronics a few times and have been satisfied with
their products and service. Their advertisements can be found in most
amateur radio magazines. I am not aware of a web presence.
Ed Cregger
ecre...@mindspring.com
Cregger
several different models with several AM and FM sets mixed so that he
couldn't tell which was which, and then have him tell us which sets were
which. <g>
I doubt if anyone could do it. My next test series would be PCM versus PPM.
Other than turning the transmitter off, I don't think most could tell the
difference between them either.
Ed Cregger
ecre...@mindspring.com
Jim White <jimw...@ij.net> wrote
> (snip)
> FWIW, I've been flying RC since 1970, and until last year ALL of my
> equipment (in scale, QM, F1 and sport) was AM, all kit-built from Ace
> and Royal kits and a few scratch built recievers.... I only changed
> because I fell in love with the Futaba 8 channel transmitter... in all
> those years, the ONLY radio related problem I've ever had was a broken
> wire on a switch.... or did that break in the crash???... no "I ain't
> got it" glitching, no unexplained by vibration twitching, and no
> flyaways....
Jim White
>I have a question about the metal shielded case. I plan on putting a 400Mhz
>ATV transmitter in my plane for video. I read somewhere that they recommend
>shielding the reciever. What would be the best way to do this? Steel, copper,
>aluminum? Also, would the shielding have to ground to anything? Any help
>appreciated, thanks, derek.
>
>
>Little gold car 1985 Toyota Tercel
>263,000 miles and counting.
>Visit a cool tercel page
>http://www.geocities.com/MotorCity/Garage/4989/4x4tercel.htm
a shield connected to nothing is often an antennae more than a
shield....
Jim White
not at all.... this was told to me by Sid gates, the former owner of
Royal Electronics....
>Its easier and cheaper to build an AM RX and TX, the means of modulation
> and detection are much simpler... Like an old crystal radio for RX...
> Its a diode, a capacitor, a coil of wire and an earpiece, that's all you need
> to make an AM RX!
let's talk apples and apples.... i.e. an FM rcvr and an AM rcvr with
similar performance in terms of selectivity and image rejection.... in
our environment this typically requires dual conversion and at least
one rf stage...
>FM, OTOH, takes complex detectors to RX the signal!
true, but THAT'S the point of the "chip" approach....
>The real reason FM is preferred is noise, static, immunity!
"Now Your copping out to preconceived ideas" Mike.... I refuse to get
baited into this one, I will only say that in MY experience, our AM
equipment performs just as well as our FM equipment, under normal
use.... I'm sure we could easily design adverse tests to prove either
one is better in some weird scenario....
>And line of sight (LOS) thinking of VHF doesn't enter into it, when a plane
> is flying its LOS is much greater than yours on the ground, so static or noise
> immunity is a real problem!
but if it's out of MY line of sight, what's the point??
>BUT for cars, boats (as others try to rationalize)... its NOT!
> AM is plenty good, being on the ground, with the same power TX and a
> shorter LOS AND a much shorter required range, the TX signal is strong
> enough to overwhelm the static/interferance problems!
>
>mike
> But then I only do Radios, Radar's, Satellite Comm systems...
> for a living, what do I know??? ;)
>
we all base our comments primarily on our own experiences, more than
our knowledge... sounds like you've had some crappy AM equipment...
FWIW, I've been flying RC since 1970, and until last year ALL of my
equipment (in scale, QM, F1 and sport) was AM, all kit-built from Ace
and Royal kits and a few scratch built recievers.... I only changed
because I fell in love with the Futaba 8 channel transmitter... in all
those years, the ONLY radio related problem I've ever had was a broken
wire on a switch.... or did that break in the crash???... no "I ain't
got it" glitching, no unexplained by vibration twitching, and no
flyaways....
Tim
Mike Here, I'm at Tim's house for the weekend...
Cregger wrote:
> All right, let's get out the ruler. Like you, I have a worthless piece of
> paper from the FCC.
I, admittedly among the extremely few, use mine almost every day,
doing electronics service and installations for the inland waterways
marine industry... Tow Boats, on call 24/7, except for a couple
weekends a month and Vac. time (like now, Yee Hawww!!!).
> Mine even includes a radar endorsement - big deal.
I install and service ships radars, Furuno, Sperry (Racal Decca now
owned by Sperry), Simrad (Anritsu)... and the occasional Toy Radars
(for pleasure boats) ... <G>
Furuno FR-2110V 10 Kw, 20" color radar New Style (narrow beam
width) 6' array, TR Up, Raster Scan, installed (locally) $20K ...
Its the current hot seller for Tow Boat companies with a decent budget.
BTW Do NOT buy an Icom M-127 Marine VHF... LEMON!!!
We've sent back more than we've sold!!!
(IOW some have gone back more than once)
> Its
> possession hardly makes me, or anyone else, a trained professional.
I totally agree, just like any license, certification, degree...
it doesn't mean squat if the person holding it doesn't really understand
the complexities involved to the point to think in them. Otherwise its
only a facade for knowledge, just a hollow echo, that the holders short
term memory was able to recall the proper answer to the question at the
proper time to pass an exam.
I OTOH am a "Trained Professional". <G>
> I hope
> you are relying on more credentials than that for your stated
> professionalism.
Just years of being an electronics hobbyist (age 8), amateur radio hobbyist
and employed in commercial service work (Trained Professional)...
Was used by my electronics teachers to help teach the others in my
class who couldn't comprehend the subject, repeatedly argued points
with my electronics teachers and always won... And as always given
the Hard assignments because the teacher knew I could pull them off,
BTW I had my 1st phone about 6 months into my formal electronics
training, the additional 2 years was just to fulfill the required credits
to graduate.
As for cred's, as you said / implied above, without the brain power
to Grock the subject matter they don't mean squat.
> I don't claim to be a radio expert and I certainly never claimed that AM was
> superior to FM. Where did that come from?
Your post...
"FM is more prone to multipath problems than AM. All you have
to do to trick it up is put it near a lot of reflective material about two
meters long to learn what I am talking about (72MHz)." - EC
This clearly states that FM (which is widely known for its noise and
interference immunity) has problems with multipath that AM does not
have.
> FM is not clearly superior to AM.
Fine, state how FM is not clearly superior to AM...
Include noise immunity...
Interference immunity...
The FM IF/Detector IC circuitry that tracks the FM signals frequency
so that even if the TX is a bit off frequency the RX self adjusts to
the center frequency, a feature AM does not have...
(Pull out an ECG Semiconductor cross reference manual with IC
op specs to verify this)...
Include arguments against the commercial, military... users all going to
FM for the VHF and above bands (except for the new and probably
classified military uses of Spread Spectrum, another advancement in
communications brought to you by Amateur Radios Experimenters)...
Also include The fact that airplanes are high altitude and have a much
longer Line Of Sight than conventional earth based comm systems
and therefore are more prone to interference...
> It is different, with characteristics that
> are useful under certain circumstances. The same can be said for AM, as is
> currently being used for air traffic control on certain frequencies.
"on certain frequencies" is the key here...
20 years ago it was on ALL Frequencies, so obviously the FAA realized
the superiority of FM, I'd bet the main reason its not been changed
"on certain frequencies" has to do with a slow transition over to FM
giving antique and collector full size aircraft the ability to maintain
communications using existing equipment.
> But
> before this goes any further, our R/C systems do not use AM or FM in the
> business/ham/CB/broadcast sense, so the arguments are moot anyway.
<Chuckle>
OK, I'll let you save face now Ed. <G>
> I'm going to stop right here as I suddenly remembered a few conversations
> that we had a while back.
I agree that that's your best option.
Take care
mike
Tim
VWhed84 wrote:
> I have a question about the metal shielded case. I plan on putting a 400Mhz
> ATV transmitter in my plane for video. I read somewhere that they recommend
> shielding the reciever. What would be the best way to do this? Steel, copper,
> aluminum? Also, would the shielding have to ground to anything? Any help
> appreciated, thanks, derek.
Hi Derek,
Mike here, at Tim's...
Ground the RX shielding (Copper or Al is better than Steel but Al foil will
work) to the negative lead (-) of the BP will be good as long as the connections
are short. Also Ferrite beads or bypass capacitors on all of the leads going to the
RX may be necessary (Not the Antenna!!!).
Mainly keep the ATV TX and Antenna as far away from the RC RX and
Antenna as Possible!
Also use as small of a ATV TX (power wise) as is possible, or some
Over Saturation of the RX is possible causing the RX range to
dramatically decrease. (Known as DeSense)
An example would be to put the RC RX forward and route its Antenna thru
the wing and to put the ATV TX in the tail and route its antenna out the tail.
Right angles to each other! This also causes a difference in polarity between
the radios and a noticeable attenuation of interference will be seen.
BUT always give your setup a good Ground Check (with the TX Antenna
collapsed) before flying!
mike
"Trained Professional" ;)
Cregger
Well, at least we agree on two points. Icom is junk equipment and you read
"Stranger in a Strange Land", so you can't be all bad.
Ed Cregger
ecre...@mindspring.com
Tim <tben...@usit.net> wrote in message news:383788AE...@usit.net...
> Hi Ed,
> Mike Here, I'm at Tim's house for the weekend...
(snip)
Cregger
Ed Cregger
ecre...@mindspring.com
Tim <tben...@usit.net> wrote
> VWhed84 wrote:
>
>
> mike
> "Trained Professional" ;)
Tim
> Mike Dumas <mi...@vci.net> wrote:
> >
> >Now Your copping out to preconceived ideas Jim!
Mike here at Tim's...
> not at all.... this was told to me by Sid gates, the former owner of
> Royal Electronics....
What's Royal Electronics (never heard of it)???
> >Its easier and cheaper to build an AM RX and TX, the means of modulation
> > and detection are much simpler... Like an old crystal radio for RX...
> > Its a diode, a capacitor, a coil of wire and an earpiece, that's all you need
> > to make an AM RX!
>
> let's talk apples and apples.... i.e. an FM rcvr and an AM rcvr with
> similar performance in terms of selectivity and image rejection.... in
> our environment this typically requires dual conversion and at least
> one rf stage...
Of course!
> >FM, OTOH, takes complex detectors to RX the signal!
>
> true, but THAT'S the point of the "chip" approach....
Say WHAT???
Do you want to explain this statement or just remain Vague?
The FM Detector/IF chip used in FM RX are able to track the TX
signal where the AM RX can NOT do this ! Advantage FM.
I don't have to rely upon others opinions, i've been into RF comm
since age 8, now 42, and I hold both Amateur and Commercial Licenses
and beyond that I Understand the complexities involved, being a
"Trained Professional" for many years in the Comm installation and
service community. I don't have to rely upon others, I understand it
on my Own!
> >The real reason FM is preferred is noise, static, immunity!
>
> "Now Your copping out to preconceived ideas" Mike....
Based upon what personal Experience???
Somebody else's claims???
So you know more than the Commercial and Military users of VHF???
> I refuse to get
> baited into this one,
BS!
You posted, therefore your opinionated and admittedly not from
personal experience but rather from what someone else said.
> I will only say that in MY experience, our AM
> equipment performs just as well as our FM equipment, under normal
> use.... I'm sure we could easily design adverse tests to prove either
> one is better in some weird scenario....
Where At??? Hmmmm???
Out in the boonies, sure, AM does good enough, I admitted to that!
BUT in RF congested areas FM is superior...
Or are you saying you know more than the commercial and military
users of Comm Equipment? Hmmmm???
I do this for a Living and a Hobby, but the Hobby interest came first!
Even my boss defers to me on matters of propagation, usable range...
And we both hold the same Licenses!
He recognizes that I have a passion for this subject along with the
practical experience of being a ham for 25 years... and therefore
defers to me on the experience that I have.
> >And line of sight (LOS) thinking of VHF doesn't enter into it, when a plane
> > is flying its LOS is much greater than yours on the ground, so static or noise
> > immunity is a real problem!
>
> but if it's out of MY line of sight, what's the point??
OK, Lets look at this....
Your TX antenna is 4-6 ' off the ground (Your LOS!) average it at 5'...
We'll ignore the fact that your TX antenna is mainly Horizontal, or
horizontally polarized, causing a non omni directional TX signal
more like a figure 8 than a 0 of a true Omni directional signal...
Meaning that when you point AT your plane it receives a minimal signal
from your TX Antenna because it radiates its best signal from its sides!!!
(Known as Broad Side Radiation)
Your plane is at 250', or 50X the altitude your TX is...
Meaning that its Line Of Sight (LOS) is 50X what your TXs is!!!
Has the light bulb (of realization) lit yet?
A AM RX is more susceptible to interference than a FM is (but don't
believe me, you haven't so far ;) contact the FCC, ARRL...)
now a AM RX at 250' can RX interference for a few hundred miles away...
Where a FM RX needs a very strong signal in order to RX interference...
Is that Light Bulb getting brighter yet???
IOW your RX sees 50X further than you OR your TX!!!
> >BUT for cars, boats (as others try to rationalize)... its NOT!
> > AM is plenty good, being on the ground, with the same power TX and a
> > shorter LOS AND a much shorter required range, the TX signal is strong
> > enough to overwhelm the static/interferance problems!
> >
> >mike
> > But then I only do Radios, Radar's, Satellite Comm systems...
> > for a living, what do I know??? ;)
> >
>
> we all base our comments primarily on our own experiences, more than
> our knowledge... sounds like you've had some crappy AM equipment...
No I haven't.
But I Know the characteristics of various equipment at various frequencies...
thru 25+ years experience! And You???
BTW experience IS Knowledge!
I was into CB at a very early age, and then graduated to Ham Radio...
I've used radios from 3.5 thru 800 mhz... as a Hobby.
I'm familiar with Troposhpheric Ducting, Normal Skip, Sunspot Cycles,
MUX... I've installed and worked on HF SSBs, VHF, Satellite...
Comm systems (both digital and audio), Loran C and Differential GPS,
Radar... As a Professional and Amateur!
> FWIW, I've been flying RC since 1970, and until last year ALL of my
> equipment (in scale, QM, F1 and sport) was AM, all kit-built from Ace
> and Royal kits and a few scratch built recievers....
I started RC in '75 with a Orbit system then went to a World Engines Max
System on 27 mhz AM, then had a Futaba AM and finally graduated to a
ProLine dual Conversion AM system on 72mhz...!
I have no bad memories of Any AM system!
OK, I admit the W.E. 27mhz had problems with CBs interfering...
But I Know that was the frequency and NOT the modulation Mode!
The ProLine AM Dual Conversion was probably the best system I ever
owned for Quality of design and Construction! Jim Fosgate had his
Shit Together!!!
But my Knowledge and Experience (decades of it) goes beyond RC...
To Commercial, Satellite... Does Yours???
> I only changed
> because I fell in love with the Futaba 8 channel transmitter... in all
> those years, the ONLY radio related problem I've ever had was a broken
> wire on a switch.... or did that break in the crash???... no "I ain't
> got it" glitching, no unexplained by vibration twitching, and no
> flyaways....
And how does this prove that AM is better than FM????
Your experience is more important than the entire commercial and
military's experiences???
Your a Ham... Get a ARRL Handbook and see what it says about
AM compared to FM! And its not even considering a RX 250'
in the air!!!
Above you admitted to "we all base our comments primarily on our
own experiences, more than our knowledge"...
And in this case you've proven your not immune to this concept!!!
mike
Jim White
consider this thread terminated, since the bulk of your posts are
nothing but chest thumping interspersed with opinions based on the
communication of analog information over long distances through
difficult terrain that you insist on applying to the communication of
essentially binary keyed or fsk information over very short distances
in a line-of-sight scenario with judicious amounts of power... you
rely on what you understand as theorey instead of your own admitted
experience..... I think I'll go flying and enjoy my trouble free
radio sets, as I've done for MY 29 years (28 yrs with AM) of
experience flying multi-channel RC....
never heard of Royal???
Tim <tben...@usit.net> wrote:
Jim White
Dersu u
When you were about 13 or 14 Royal was one of the domestic makers of radio
equipment. Their purple box was found at a good many flying sites around the
country.
Michael Neverdosky
> Well I've only been a FCC licensed Commercial Radio Technician since 76,
> First Phone and then PG class license... So i admit i don't know everything.
I don't recall any questions pertaining to RC in any of the FCC tests
when
I got my first phone with radar endorsement.
> If AM is so much better why did the R/C industry upgrade to FM
> AND why aren't any PCM radios offered on AM?
> Would you pay $1500 for a high end AM Futaba radio???
Mainly because of a public perception that FM is better than AM.
Perception, not reality sells radios.
The truth is that given the same bandwidth both have the same resistance
to interference, over all.
The AM radio is slightly more suseptable to static interferance and the
FM is more susceptable to capture.
> A Lightening Strike 2 states away can cause a Static Crash on a AM radio
> BUT not on a FM radio.
Are you using broadcast radio as an example?
Bad choice because of the VERY different frequencies used.
FM and AM radios on the SAME FREQUENCY will both hear the lightning
about
the same, not exactly but close.
Broadcast FM at 88-108 megacycles gets a lot less lightning static
because
there is a lot less energy that high in frequency than there is at
600-1500
kilocycles of the AM broadcast.
> Commercial radios in the VHF Low (well below 72mhz.) thru Microwave
> (well above 72mhz.) bands including Cell Phones upgraded to/use
> FM for a reason, less inherent noise problems under all conditions.
That is the normal argument but it was really the relaxed need for
accurate
frequence control that won the day. Especially in the days of all tubes.
> Hey, I'm only a trained and experienced professional, what do I know? ;)
But are you a trained and experienced professional in RC systems?
michael N6CHV (also first phone with radar endorsement)
Michael Neverdosky
> Fine, state how FM is not clearly superior to AM...
> Include noise immunity...
>
> Interference immunity...
>
> The FM IF/Detector IC circuitry that tracks the FM signals frequency
> so that even if the TX is a bit off frequency the RX self adjusts to
> the center frequency, a feature AM does not have...
A very nice feature it is too,,,,, until stronger signal appears on or
near your operating frequency. Then 'capture' can happen where the
discriminator
locks onto the unwanted signal and completely keeps the desired signal
out.
> Include arguments against the commercial, military... users all going to
> FM for the VHF and above bands
The last time I checked, all of the military 225-400 Mhz systems were
AM.
> Also include The fact that airplanes are high altitude and have a much
> longer Line Of Sight than conventional earth based comm systems
> and therefore are more prone to interference...
Avoidance of capture is the reason all VHF airplane com radios are AM.
They want to hear (or at least know that the signal is there) the weak
signal
of the plane calling for help, even when a stronger signal in present.
> > before this goes any further, our R/C systems do not use AM or FM in the
> > business/ham/CB/broadcast sense, so the arguments are moot anyway.
Right, in that the AM is actually pulse modulation.
Actually, if you want to get real improvement you need to go to the
newer
error correcting codes for transmitting the information. Error
correction
gets you lots more resistance to interferance than anything else.
The price is the need for computer power in both the transmitter and the
receiver. In todays world this is not so much of a problem.
Given the same transmitter power and receiver bandwidth, signal to noise
will be the same (or very close, there are some exceptions) regardless
of
the modulation used.
BTW You are FAR more likely to be shot down by someone turning on a RC
transmitter on your frequency on the same field, than ANY other source.
michael
Michael Neverdosky
> > ... truth be known the REAL
> > reason for using FM is the availability of those chips developed for
> > all of the commercial FM applications...
>
> Its easier and cheaper to build an AM RX and TX, the means of modulation
> and detection are much simpler... Like an old crystal radio for RX...
> Its a diode, a capacitor, a coil of wire and an earpiece, that's all you need
> to make an AM RX!
But NOT a RX for RC!
Look in the data books, chips for AM are becoming scarce and FM chips
containing nearly everything to make the RX are less than a dollar each.
> The real reason FM is preferred is noise, static, immunity!
Not really.
Greater ability to handle signals off frequency is the main traditional
benifit of FM.
In RC models the perception that FM is 'better' is the primary reason.
Any marketing person can tell you that what people think is far more
important
than what is true.
michael
Michael Neverdosky
> And how does this prove that AM is better than FM????
I have not seen anyone make this claim.
AM and FM are not significantly different in performance
in radio control systems.
Remember, the definition of a good radio is, "One that works."
No more no less.
In RC applications, Not commercial, not radars, not satelites,
both FM and AM have the same transmitter power, and the same bandwidth,
therefore they have the same signal to noise ratio.
Neither one is better than the other, they are just different.
michael
Michael Neverdosky
> never heard of Royal???
Shows his huge amount of experience in RC.
:-)(
michael
Ian Maclaughlin
<snipped>
>Mainly because of a public perception that FM is better than AM.
>Perception, not reality sells radios.
>
>The truth is that given the same bandwidth both have the same resistance
>to interference, over all.
<more snipped>
Michael-
I wondered when somebody would point out the fact that the FM mode
advantage is highly dependent on the bandwidth available. I'm very
much in agreement with you regarding 'perception,' too. Wonder what
the perception would be if we called a spade a spade - i.e. FSK
instead of FM? As I'm sure you know, the clipping that is primarily
responsible for cleaning up a broadcast FM signal won't remove noise
from a signal design based on 2 frequency bins and binary 'signal
present or not' decisions.
Ian
San Diego
Michael Neverdosky
Even still FM is slightly more resistant to impulse noise and static and
AM is slightly more resistant to capture.
Both will crash when another transmitter on the same channel is turned
on
at the same flying field. This is the most common form of interferance
that causes a crash. Next is the kind that comes from things like moving
the sticks wrong or forgeting to charge the batteries.
:-)(
I haven't seen any tests but FM may have a slight advantage in a plane
with an ignition engine, but that has never been the case in any
of my sailplanes or electrics.
BTW I have not seen any difference in performance of FM and AM in
electric powered models running brush motors.
michael
Mike Dumas
I never wash my car Ed, so once again your mistaken. ;)
mike
Mike Dumas
Cregger wrote:
> OH YEAH! <G>
>
> Well, at least we agree on two points. Icom is junk equipment and you read
> "Stranger in a Strange Land", so you can't be all bad.
Don't get me started on Icom!
I never liked their ham equipment
and learned to hate ther marine equipment. <G>
'Stranger..." is one of my all time favorite books
as is 'The Moon is a Harsh Mistress' ...
Heinlein had a way with words.
Take Care Ed.
mike
Mike Dumas
Royal. the RC company, yes.
Royal Electronics?
That company could make anything from Mr Coffee Controllers,
to competing with Racal and Raytheon for military contracts for all I
know.
But its a common ploy on NGs, when loosing an argument, to make
comments about unimportant details, like company names, a mispelled
word... to divert attention from the real core of the topic.
Did Royal Electronics make RC Engines, starters, power panels...
under the Royal name?
Just because I don't waste the time to research the company
for every item I purchase, doesn't by default, mean I know
nothing about RC.
mike
Mike Dumas
Michael Neverdosky wrote:
> But NOT a RX for RC!
> Look in the data books, chips for AM are becoming scarce and FM chips
> containing nearly everything to make the RX are less than a dollar each.
Your right...
The perferred FM mode made the Semiconductor companies put more effort
into making IC's for them, and as newer MFG techniques and more and more
demand drive the Semiconductor industry, the price has dropped very low.
(Case In Point: the first 486 CPUs sold for $1000 at OEM QTY and Pricing.
Now you can buy a 200 (or more) times faster CPU, with 10+ times the
number of on chip components for $40 every day)
AM OTOH still is simpler to detect and no ICs are required except in the
decoder stage, and both AM and FM can use the same Decoder ICs.
Selectivity is not in the IC's its in the Q of the Ciruitry and the filters used!
Now factor in the across the board drop in RC TX and RX prices
from the 70's! For what a Futaba 4-5 channel AM setup cost you
back then, you now can have a programmable FM radio.
AND thats figuring dollar for dollar, not including the inflation...
which would be closer to being able to buy a $1k computer radio
for the same inflated dollar value.
> > The real reason FM is preferred is noise, static, immunity!
>
> Not really.
> Greater ability to handle signals off frequency is the main traditional
> benifit of FM.
> In RC models the perception that FM is 'better' is the primary reason.
My perception came from Hams and Commercial Services who like
me were there, seeing the benifits of FM over AM at the time of the initial
change over in those services.
This is the peak of the 11 year sunspot cycle, and there IS more noise on
AM in ALL bands i've monitored, than is heard in FM mode. To really
hear th difference flip over to SSB (a sub class of AM). WOW its noisy!
> Any marketing person can tell you that what people think is far more
> important
> than what is true.
>
> michael
For Joe Average, who doesn't have a clue at to the reality of the situation???
Yes, this is true. But i'm not Joe Average, i've been interested in
communications, studied, built and used equipment... since the late 60's.
Now I work on it.
I, obviously unlike you, am not corrupted by ad hype and its thinking as the
basis for my opinion. I've been there and done that.
Cell Phones are FM!
They were put into service initally to give the highest quality communications
at a affordable price! The intention was not to Sell Equipment as the main
source of their Income, BUT to Sell Usage Time!!!
Higher Quality = More Usage!!!
Watercom, (an Inland Waterways Based phone system) a predicessor of
Cell Phones is also FM, they Provide equipment for $1 per month and make
their money on Usage Fees!!!
Funny how even the engineers who aren't designing comm equipment as a
For Sale (more profit) Item, keep prefering FM to AM...
But you, in your infinate wisdom know more than they do, don't you???
<BG>
Now tell us what you fly, AM or FM???
mike
Mike Dumas
Dersu u wrote:
Dug out an old 66 RC Modeler... (BTW I was 9 then)
BUT the name is ... Royal Products Corp.
not Royal Electronics.
Unless RE was yet another Co.
mike
Mike Dumas
Now I know why I didn't remember them!
Selling early 70's looking equipment in the 80's...
By then I had Pro Line and paid no attention to off brands,
especially outdated off brands.
Jim White
Pro-Line was a Johnny come-lately but did make excellent stuff....
Mike Dumas <mi...@vci.net> wrote:
Jim White
Jim White
FYI, Royal was the Number 5 maker of RC equipment (behinf Kraft,
Cannon, MRC and EK-Logictrol) in the early 70's and continued
manufacturing untill about 1988....
Mike Dumas <mi...@vci.net> wrote:
>
>Royal. the RC company, yes.
>
>Royal Electronics?
> That company could make anything from Mr Coffee Controllers,
> to competing with Racal and Raytheon for military contracts for all I
>know.
>
>But its a common ploy on NGs, when loosing an argument, to make
> comments about unimportant details, like company names, a mispelled
> word... to divert attention from the real core of the topic.
>
> Did Royal Electronics make RC Engines, starters, power panels...
> under the Royal name?
>
>Just because I don't waste the time to research the company
> for every item I purchase, doesn't by default, mean I know
> nothing about RC.
>
>mike
>
>
>Michael Neverdosky wrote:
>
>> Jim White wrote:
>>
>> > never heard of Royal???
>>
>> Shows his huge amount of experience in RC.
>>
>> :-)(
>>
>> michael
Jim White
Jim White
Royal Products was a front for an importer of stuff from the far
east... tachs, servos, fuel pumps... i.e. acessories.... never made
or sold Radio Systems.... Royal Electronics was stationed in Denver...
Mike Dumas <mi...@vci.net> wrote:
Jim White
Jim White
this guy still doesn't get it.... transmitting voice and hearing
"static" is not the same as FSK or keyed CW....
Mike Dumas <mi...@vci.net> wrote:
Michael Neverdosky
> I, obviously unlike you, am not corrupted by ad hype and its thinking as the
> basis for my opinion. I've been there and done that.
That is why you keep spounting the same old line from the marketing
departments about how FM is so much better than AM.
Show us the facts?
Present the test results and engineering data.
> Cell Phones are FM!
So?
Cell phones are not RC equipment.
Also, they are FM mainly because of the frequency capture you talked
about
earlier. If a phone is a little off frequency it is handled without
any noticible problem to the user.
A SSB cell phone would use far less power and have greater range but the
cost
and size of the crystal oven oscillator needed for frequency control
would
take it out of the market.
> Funny how even the engineers who aren't designing comm equipment as a
> For Sale (more profit) Item, keep prefering FM to AM...
But profits are their goal, not equipment performance.
Their equipment only has to be 'good enough'.
For that matter so does RC equipment. If it maintains control during the
use that it is put to, then it is a good radio.
> But you, in your infinate wisdom know more than they do, don't you???
I never said any such thing.
I also never claimed that AM was better than FM.
You are claiming that FM is so much better than AM that someone would
have to be stupid to fly AM. Did I get that right?
The truth is, both AM and FM WORK.
> Now tell us what you fly, AM or FM???
Depends on the radio I am using.
Unlike you, I have not bought into the FM hype. I will happily
use iether one and enjoy it.
If I had the choice I would use a system with a low bandwidth phase
shift
modulation and error correcting code. The error correcting code is the
key
not the choice of modulation.
If you look at the research you will find that there is no amount of
power
or signal to noise ratio that will result in error free communication.
Error correcting codes do produce error free commnication with very low
power and don't care what modulation you use to get them there.
michael N6CHV (I also have a first phone, radar endorsement, so what)
bills...@my-deja.com
Dear Jim:
Why don't you switch the discussion to FM vs. PCM (digital) which I
would find much more interesting.
All modern, more sophisticated computer radios are either FM or digital.
Also there is a significant price differential between FM and PCM
receivers.
Bill Stanley
In article <o5ep3s8732kmm0286...@4ax.com>,
> >I, obviously unlike you, am not corrupted by ad hype and its thinking
as the
> > basis for my opinion. I've been there and done that.
> >
> >Cell Phones are FM!
> > They were put into service initally to give the highest quality
communications
> > at a affordable price! The intention was not to Sell Equipment as
the main
> > source of their Income, BUT to Sell Usage Time!!!
> > Higher Quality = More Usage!!!
> >
> >Watercom, (an Inland Waterways Based phone system) a predicessor of
> > Cell Phones is also FM, they Provide equipment for $1 per month and
make
> > their money on Usage Fees!!!
> >
> >Funny how even the engineers who aren't designing comm equipment as a
> > For Sale (more profit) Item, keep prefering FM to AM...
> >
> >But you, in your infinate wisdom know more than they do, don't you???
> >
> ><BG>
> >
> >
> >Now tell us what you fly, AM or FM???
> >
> >mike
> >
> >
> >
>
> Jim White
> AMA 2466
> WB2WOY
> WPMPA/BCF/PFC
> SouthShoreSoftware
Sent via Deja.com http://www.deja.com/
Before you buy.
Michael Neverdosky
a separate issue from FM and AM. They are not really the type of
modulation
but how the information is incoded.
PPM has the information in the length of space between pulses sent by
the
transmitter. The length of space varies with the position of the stick
on the transmitter and is decoded into a PWM (pluse width modulation)
signal to drive the servo. The information is in analog form all the
way.
PCM sends a digital word that has the information to be
decoded by the computer in the receiver. The information is in digital
(binary number) form during transmission and reception and is usually
decoded to PWM to drive standard servos by the receiver.
PCM has the advantage of allowing the receiver to know if it is
receiving
valid information or not. This means the receiver can act on only good
information and choose a 'fail safe' mode when there is interferance.
PPM has the advantage that both the receiver and transmitter can be
simpler and lighter. For minimum cost or minimum weight PPM has the
edge.
For a little more money and a little more weight the PCM will give you
a more reliable link.
Now for the question of PCM radios being FM (are there still any
available
in AM?). As the strong perception of FM being 'better' than AM, builders
are going to make their high end systems FM. It is just good marketing.
There is really no reason for them to complicate the production by even
offering AM in their PCM systems.
Now, if they would add error correcting codes to the PCM systems then
we would have systems that were FAR more reliable.
The one big downside to PCM and the future use of error correcting?
The ability to mix equipment from different models and makers will
get to be a lot less than it is now. Unless of course we can get
all of the radio makers to use the same code.
michael
Jim White
>November 25, 1999
>
>Dear Jim:
>
>Why don't you switch the discussion to FM vs. PCM (digital) which I
>would find much more interesting.
>
>All modern, more sophisticated computer radios are either FM or digital.
>Also there is a significant price differential between FM and PCM
>receivers.
>
>Bill Stanley
>
actually, they're both FM (actually they're both FSK, but why go
there...), the modulation envelope is either PPM or PCM.... in MY
opinion, as currently implemented, there is no compelling reason to go
with PCM.... again, as it exists today....
Jim White
AMA 2466
WB2WOY
WPMPA/BCF/PFC
SouthShoreSoftware
Treasure Island, FL
Daytripper
>Michael Neverdosky <mneve...@earthlink.net> wrote:
>>For a little more money and a little more weight the PCM will give you
>>a more reliable link.
>
>Does PCM have forward error corection ? No
True. But it does offer forward error detection, discarding bad frames.
>A better SNR ? No
Depends on how you characterize "Signal to Noise Ratio", doesn't it?
If a receiver drops bad frames on the floor instead of twitching a servo,
isn't that a noise filter in function? And if "noise is reduced" could not one
say that the S/N ratio is thus improved?
>I don't see how the HF link is improved by PCM.
Of course not - the HF link is essentially unchanged: FM is FM, and as
measured from the input of the FM modulator to the output of an IF strip
buried within the RX, nothing has been changed.
But if you spread the measurement points out a bit further, there is clearly
an improvement in the overall functionality of the system - by virtue of the
superior data integrity between stick and servo.
>The only, questionable, advance is the signal hold option of the
>receiver.
>
>BTW Multiplex intruduced a hold option and double super receivers in
>PPM and gets the same results as PCM systems.
>
>PCM adds nothing, its a missed opportunity to fundamentally improve
>our systems.
That's debatable (which is good - if not for debate, why Usenet? ;^) With all
due respect, I think you're too absolute in your assessment. PCM clearly
offers a benefit. The question is whether that benefit is worth the premium.
I don't own any PCM receivers, though two of my three FM systems are PCM/PPM
switchable. While I have an appreciation for what PCM offers, I don't feel the
improvements justify the ridiculous prices (I mean we're talking about a
feature that shouldn't cost more than a buck or so when embedded in a chip)...
Cheers.
/daytripper
Phil Cole
this subject.
In summary, I wandered around the field comparing
PPM and PCM receivers, and PCM showed better range
by a factor of two or more. Unless someone was
maliciously jamming my PPM tests, the PCM receivers
I used would appear to have 6 dB better
SNR. (Twice the range: quarter the received power).
I was convinced that the money is worth spending on
models that are expensive to crash (both model and
liability expenses).
"Ton C. Jaspers" wrote:
>
> Michael Neverdosky <mneve...@earthlink.net> wrote:
>
> <big snip>
>
> >For a little more money and a little more weight the PCM will give you
> >a more reliable link.
>
> Please explain ?
> Does PCM have forward error corection ? No
> A better SNR ? No
> I don't see how the HF link is improved by PCM.
> The only, questionable, advance is the signal hold option of the
> receiver.
>
> BTW Multiplex intruduced a hold option and double super receivers in
> PPM and gets the same results as PCM systems.
>
> PCM adds nothing, its a missed opportunity to fundamentally improve
> our systems.
>
> Ton
--
Phil
Ton C. Jaspers
Jim White
>our systems.
>
>Ton
valid point....
Michael Neverdosky
>
> Michael Neverdosky <mneve...@earthlink.net> wrote:
>
> <big snip>
>
> >For a little more money and a little more weight the PCM will give you
> >a more reliable link.
>
True
> A better SNR ? No
True
> I don't see how the HF link is improved by PCM.
The actual link is not improved, just as error correction does not
improve
the HF link, it just improves the reliability of the information sent
to the servos.
> The only, questionable, advance is the signal hold option of the
> receiver.
I would not call it a questionable advance but rather a small one.
One thing we forget here (also in the PCM contributes to fatality
thread) is
that there is a big difference between aircraft. A slow trainer does not
react to glitches but only to sustained control inputs. I have seen
gliders
(trainers) that were getting full control throw glitches with very
little
change to the flight of the plane. The same problem in a high
performance
fast and highly tuned competition plane would cause major flight path
changes
if not an instant crash.
The PCM system will not pass bad info to the servos, it will either hold
of
go to a preset 'failsafe' setting.
Again there is a difference between the trainer and the performance
ship.
Many trainers (sailplanes) given full up elevator and full rudder will
either
spin (very safe) or spiral dive (somewhat faster but still pretty safe
given
the limited speed capability of the trainer) while there is no set
control
surface setting on the high performance plane that is sure of giving you
anything predictable, other than a crash.
Given that the standard use os error correcting codes in modems has only
happened in the last 10 years it is not a surprise that they are not yet
in models, a much smaller market.
Error correcting codes and some way for the receiver to signal problems
"in flight" are really the way to go, and we will probably see them in
the
next several years.
michael
Michael Neverdosky
> But if you spread the measurement points out a bit further, there is clearly
> an improvement in the overall functionality of the system - by virtue of the
> superior data integrity between stick and servo.
And the integrity between stick and servo is what really matters in RC,
everything else is window dressing.
While I am a technogeek and care about how the systems work when I am
flying a plane all I really care about is keeping control. While hanger
flying all the rest of the stuff is important. :-))
> While I have an appreciation for what PCM offers, I don't feel the
> improvements justify the ridiculous prices (I mean we're talking about a
> feature that shouldn't cost more than a buck or so when embedded in a chip)...
Here is where expanding the ranks of RC fliers will help. The more units
of
a particular radio get sold the more the R&D cost get spread out.
I could make you a radio system that would completely outclass
everything
out there today and sell it for less. There is a catch, you have to buy
250,000 units the first year, 500,000 units the second year, and a
million
units a year after that. Care to make a guess when the market is
saturated?
The radio makers don't have an easy time of it. They have to keep
innovating
in a market with fairly few sales and not a lot of money.
Check with any electronics supplier and see the price difference between
buying 1, 10, 100, 1000, and 100,000 of an item. In large quantities the
cost
is often less that a quarter of the unit price.
michael
Michael Neverdosky
Not real life testing of the link between stick and servo.
My god, like someone actually flies and cares more about control
than theory.
:-)))
:-)))
Humor alert!
The tone of my message is humorous.
The point is not.
Control is the whole point.
michael
Ton C. Jaspers
>PPM (pulse position modulation) and PCM (pulse coded modulation) are
>a separate issue from FM and AM. They are not really the type of
>modulation
>but how the information is incoded.
Agree
>PPM has the information in the length of space between pulses sent by
>the
>transmitter. The length of space varies with the position of the stick
>on the transmitter and is decoded into a PWM (pluse width modulation)
>signal to drive the servo. The information is in analog form all the
>way.
Agree
>PCM sends a digital word that has the information to be
>decoded by the computer in the receiver. The information is in digital
>(binary number) form during transmission and reception and is usually
>decoded to PWM to drive standard servos by the receiver.
Agree
>PCM has the advantage of allowing the receiver to know if it is
>receiving
>valid information or not. This means the receiver can act on only good
>information and choose a 'fail safe' mode when there is interferance.
Define 'fail safe'
You can't mean a full throttle crash is 'fail safe'.
I guess you are refering to the 'hold mode' during a (temporary) loss
of signal. That is not a virtue of PCM as proved by the latest
Multiplex PPM receivers. They recognise a loss of the PPM puls or an
impossible fast change of it and enter a hold mode if detected, Same
result as with PCM.
>PPM has the advantage that both the receiver and transmitter can be
>simpler and lighter. For minimum cost or minimum weight PPM has the
>edge.
PCM is inside the software of the TX chip, complexity of hardware is
the same as a PPM TX. All the extra goodies you pay for in most PCM
TX-es have nothing to do with the PCM data transer. A simple PCM TX
should not be more complex than a simple PPM TX. The receiver is a
different story however. PCM needs a double super due to bad
performance of the digital link. I dont see why a DS RX should be
significantly heavier, more expensive Yes.
>For a little more money and a little more weight the PCM will give you
>a more reliable link.
Not true, it gives you a lot, but not a more reliable link. Don't
confuse a better (more expensive) receiver with a more reliable link.
Or interpret extra functionality (hold mode) as a better link. If you
spend enough a PPM link can be made just as reliable.
>Now for the question of PCM radios being FM (are there still any
>available
>in AM?). As the strong perception of FM being 'better' than AM, builders
>are going to make their high end systems FM. It is just good marketing.
>There is really no reason for them to complicate the production by even
>offering AM in their PCM systems.
>Now, if they would add error correcting codes to the PCM systems then
>we would have systems that were FAR more reliable.
Yes, and forward error correction to be specific, the digital way to
improve SNR. It would allow a digital link with single conversion
receivers (cheaper).
>The one big downside to PCM and the future use of error correcting?
>The ability to mix equipment from different models and makers will
>get to be a lot less than it is now. Unless of course we can get
>all of the radio makers to use the same code.
I hope so, but I also would like to see some other technologies
incorporated. Just have a peak at what is happening with the digital
cellular phones for example. As usual the RC manufacterers are some
20+ years behind in technology.
Ton
Jim White
I suggest you go study up on why we use double conversion recievers
NOW.... and, oh, our ppm recievers are double conversion as well....
t...@xs4all.nl (Ton C. Jaspers) wrote:
Jim White
Mark Morgan
>
>I suggest you go study up on why we use double conversion recievers
>NOW.... and, oh, our ppm recievers are double conversion as well....
>
>
>t
At the risk of seeming like the newvie (to RC flying) that I am we
are only using double converertion not triple convertion like most of
my ham gear
Jim White
right.... but what's your point??? did someone say triple
conversion???
Dick
Give a clue what you mean with digital cellular phones, please.
Thanks. Dick
Phil Cole
Mark Morgan wrote:
>
> On Sat, 27 Nov 1999 15:13:21 GMT, Jim White <jimw...@ij.net> wrote:
>
> >
> >> At the risk of seeming like the newvie (to RC flying) that I am we
> >>are only using double converertion not triple convertion like most of
> >>my ham gear
> >
> >right.... but what's your point??? did someone say triple
> >conversion???
>
> My Point? Well at the time of posting merely curious, and
> surprised at the implication that double conversation system seems to
> considered advanced in your radio gear. Rechecking my gear I do have
> a double version tranceiver, it the one I the most trouble with
> interefence from.
In the RC application, double conversion overcomes all the applicable
problems.
You need a last IF low enough to get high gain and selectivity at
low power and small size. Ceramic filters at 455 kHz are readily
available. You can't get good image rejection with that IF frequency.
Something like 10.7 MHz for a 1st IF will get you good image rejection,
and a simple wide crystal or ceramic filter will be sufficient to
reject images from the 1st IF to the 2nd IF. If it were possible to
build a nice small cheap filter at 10.7 MHz that could give good
adjacent channel rejection 10 kHz away, then you wouldn't need the
second
IF. However all the filters I've seen at 10.7 MHz that can do
this have been larger than the receivers we use, and would double the
component cost.
Adding a 3rd IF would only create the possiblity for more spurious
responses. Not only image freqencies, but direct feed through into
the IF, and intermodulation products due to all those oscillators
and mixers in a small package without much opportunity for shielding.
Ham receivers use triple conversion for other reasons. The first IF
may actually be above the receivers operating range, then down to
455 kHz or lower in two steps. Putting the 1st IF outside the
receiver's operating range makes it possible to have a non-tuned
front end, so you don't have to keep tweaking a preselector as
you tune across the bands. All the tuning know has to do then
is control the synthesiser generating the main VFO frequency.
--
Phil
Mark Morgan
>
>> At the risk of seeming like the newvie (to RC flying) that I am we
>>are only using double converertion not triple convertion like most of
>>my ham gear
>
>right.... but what's your point??? did someone say triple
>conversion???
My Point? Well at the time of posting merely curious, and
surprised at the implication that double conversation system seems to
considered advanced in your radio gear. Rechecking my gear I do have
a double version tranceiver, it the one I the most trouble with
interefence from.
A few more thoughts, has no one tried using subcarriers to id
one transmitters, would at least keep someone else on the same freq
from sending signals to your plan. You'd just have to worry about
jamming each other in event some one defeated what ever precautions a
given flied uses to prevent two avctive units from being on the freq,
but would still have a decent chance of controling your craft
>
Jim White
good post.... I would add that one must consider the application....
Ham rcvrs are designed to be able to extract very weak signals (from
long distances) out of a very noisey (from adjacent channels possibly
only a few hundred Hz away) environment, whereas RC equipment is
designed to relaibly capture a relatively strong, local signal in a
well-spaced signal environment...
Jim White
Steve
I pushed off using PCM for cost, and failsafe issues, for quite some time.
Then, I keep noticing that those with the PCM receivers were range
checking their systems way way beyond all my PPM receivers. I decided
to test one. Same plane, same transmitter, only the receiver was swapped
out with a PCM receiver. I was out in the sticks on my next range check.
From around 50 paces on the 6 PPM receivers I have, to well over 113
paces with the PCM receiver. I put a PCM receiver in a new 38% Christen
Eagle I just acquired, and the same results. 121 Paces. I think I may be
sold on the range benefits of PCM.
Steve
medi...@mindspring.com
RC web Site www.avcomproductions.com/planes.htm
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Phil Cole <pc...@pacbell.net> wrote:
>I just made a posting in the 'hold/failsafe' thread on
>this subject.
>
>In summary, I wandered around the field comparing
>PPM and PCM receivers, and PCM showed better range
>by a factor of two or more. Unless someone was
>maliciously jamming my PPM tests, the PCM receivers
>I used would appear to have 6 dB better
>SNR. (Twice the range: quarter the received power).
>
>I was convinced that the money is worth spending on
>models that are expensive to crash (both model and
>liability expenses).
>
>"Ton C. Jaspers" wrote:
>>
>> Michael Neverdosky <mneve...@earthlink.net> wrote:
>>
>> <big snip>
>>
>> >For a little more money and a little more weight the PCM will give you
>> >a more reliable link.
>>
>> Please explain ?
>> Does PCM have forward error corection ? No
>> A better SNR ? No
>> I don't see how the HF link is improved by PCM.
>> The only, questionable, advance is the signal hold option of the
>> receiver.
>>
>> BTW Multiplex intruduced a hold option and double super receivers in
>> PPM and gets the same results as PCM systems.
>>
Jim White
at the risk of a flame war, might I suggest you consider the
difference between "range" and "effective range" for lack of better
terminology.... maybe the thing to do is range check your installation
with PPM, then add the PCM for insurance.... the point being that the
difference in range you are seeing is a result of the PCM rcvr
"masking" the errors that the PPM rcvr is getting, not "eliminating"
the errors.... I understand that under NORMAL conditions the
difference is moot, but....
maybe the mfg's should make switchable rcvrs (with the 8th channel?),
so that we could easily determine the true integrity of the
signal......
Steve <Xmed...@mindspring.com> wrote:
>I pushed off using PCM for cost, and failsafe issues, for quite some time.
>Then, I keep noticing that those with the PCM receivers were range
>checking their systems way way beyond all my PPM receivers. I decided
>to test one. Same plane, same transmitter, only the receiver was swapped
>out with a PCM receiver. I was out in the sticks on my next range check.
>From around 50 paces on the 6 PPM receivers I have, to well over 113
>paces with the PCM receiver. I put a PCM receiver in a new 38% Christen
>Eagle I just acquired, and the same results. 121 Paces. I think I may be
>sold on the range benefits of PCM.
>
>Steve
Jim White
Phil Cole
In article <nhk74s8p6dklnmila...@4ax.com>, Jim White
<jimw...@ij.net> wrote:
> at the risk of a flame war, might I suggest you consider the
> difference between "range" and "effective range" for lack of better
> terminology.... maybe the thing to do is range check your
> installation
> with PPM, then add the PCM for insurance.... the point being that
> the
That is pretty much my attitude. Radios are basically noisy
and unreliable, so they need all the help they can get.
> difference in range you are seeing is a result of the PCM rcvr
> "masking" the errors that the PPM rcvr is getting, not
> "eliminating"
> the errors.... I understand that under NORMAL conditions the
> difference is moot, but....
Radio links are fundementally noisy. Any 'professional' radio data
link uses some form of error detection, correction, diversity
to improve the odds of getting the correct data out of the
receiving end. In other word, the system designers expect the
radio parts to be less than perfect, and do what they can
to get around the problem. There is a limit to how powerful
they can make the transmitters, how sensitive the receivers,
and how much radio regulations can control interference.
The problem with PPM using the average decoder you find in a
$US60 receiver is that once you get a hit, the rest of the
frame is corrupted. All the channels shift up or down,
depending on whether you got an extra pulse, or missed one.
A PCM receiver will only mess up the data bits that actually
got hit. Of course, if the most significant bit gets hit,
the servo will want to jump half the throw. The error detection
prevents this happening. Even if the error detection
was not there, the servo would get sent back 20 ms later.
Since 1/2 travel would take 70 ms in the fastest servo, and
double that for most, you would get a jump of about 15 degrees
in the servo, then it would go back.
In a simple PPM system, multiple servos will want to jump.
With a frame pulse of 10 ms, and channel pulses of 1.5 ms,
the chance of all the servos jumping is about 0.5.
The other thing with PPM is that even when not getting
missing or added pulses, a bit of noise can affect operation.
If you want a resolution of 0.001 (= 1024 PCM), then
you need 1.5 ms / 1000 = 1.5 us accuracy in the recovered
pulses at the receiver. With a Rx BW of 10 kHz, you can
get a risetime of 100 us at the FM demodulator output.
This means that any noise can affect the pulse width
by a factor of 100 us/1.5 ms = 0.07.
The effect of this is that as noise increases (signal
weakens) the servos will jitter more and more until
eventually frames start getting corrupted.
PCM consists of a stream of 400 us pulses. It's easy
to filter the demodulator output so that anything
shorter doesn't get through. All the decoder has to
do is decide whether the signal was a '1' or '0' every
400 us instead of measuring pulse widths down to 1.5 us.
I suspect this is why PCM receivers exhibit greater
ranges than PPM receiver.
PCM works perfectly until it does not work at all.
This sudden death seems to be the most common objection.
The difference between AM and FM is similar. AM
will degrade gracefully, and FM will work well until the
signal gets noisy, then go from good to bad in a hurry.
You will notice when comparing AM and FM broadcast reception.
Even allowing for the different propagation of MW and VHF,
AM stations just get weaker and weaker over many miles,
but FM goes from good to bad in a short distance.
So, if the graceful degradation failure mode is desirable,
then AM is perferable to FM.
The IPD receivers can deal with the missing/added pulses
in most cases, by making assumptions about min pulse
widths and how fast your thumbs move, and maybe take
a exponential time average for each channel. Eventually
the receive will decide that it's receiving all noise,
and hold/failsafe, just like PCM.
> maybe the mfg's should make switchable rcvrs (with the 8th
> channel?),
> so that we could easily determine the true integrity of the
> signal......
A LED or beeper that indicates when a bit error is detected
would be very useful. Make it bright or loud, and you could
have a warning while flying around.
> Steve <Xmed...@mindspring.com> wrote:
> >I pushed off using PCM for cost, and failsafe issues, for quite
> some time.
> >Then, I keep noticing that those with the PCM receivers were range
> >checking their systems way way beyond all my PPM receivers. I
> decided
> >to test one. Same plane, same transmitter, only the receiver was
> swapped
> >out with a PCM receiver. I was out in the sticks on my next range
> check.
> >From around 50 paces on the 6 PPM receivers I have, to well over
> 113
> >paces with the PCM receiver. I put a PCM receiver in a new 38%
> Christen
> >Eagle I just acquired, and the same results. 121 Paces. I think I
> may be
> >sold on the range benefits of PCM.
> >
> >Steve
> Jim White
> AMA 2466
> WB2WOY
> WPMPA/BCF/PFC
> SouthShoreSoftware
> Treasure Island, FL
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Mike Dumas
Michael Neverdosky wrote:
> Mike Dumas wrote:
>
> > I, obviously unlike you, am not corrupted by ad hype and its thinking as the
> > basis for my opinion. I've been there and done that.
>
> That is why you keep spounting the same old line from the marketing
> departments about how FM is so much better than AM.
How could what I said possibly get translated to receive that reply???
I've been there, Before the RC AD Hype...
So how am I corrupted after the facts???
With this type of thought process on your part,
no wonder you can't determine the facts.
> Show us the facts?
To dispute which facts that you've shown???
You can't support your position so you
want me to support mine? LOL.
So the fact that almost every service has converted to FM,
even ones where it was More Expensive for the providers to do so
means nothing to you???
That the Engineers looked at more data than you could ever read
and Chose FM, means nothing to you???
> > Cell Phones are FM!
>
> So?
> Cell phones are not RC equipment.
So?
You think RC equipment interference is different from all other forms
of comm equipment just because its used for controlling a plane?
It uses different RF???
It uses different FM???
IT uses Magic???
LOL
> Also, they are FM mainly because of the frequency capture you talked
> about
> earlier. If a phone is a little off frequency it is handled without
> any noticible problem to the user.
Just like it is every day by RCers who swap Xtals and fly FM radios
on different frequencies Without Retuning the RX to the TX!
You want RC examples, there you are.
> A SSB cell phone would use far less power and have greater range but the
> cost
> and size of the crystal oven oscillator needed for frequency control
> would
> take it out of the market.
That's not true, PLL VCOs, do it every day billions of times on SSB radios
used by Ham Radio Operators...
BUT Why now switch to SSB, you've been arguing normal AM which
has a carrier so inserting a frequency by the RX isn't needed.
Obviously you know how dumb a AM cell phone would be.
> > Funny how even the engineers who aren't designing comm equipment as a
> > For Sale (more profit) Item, keep prefering FM to AM...
>
> But profits are their goal, not equipment performance.
> Their equipment only has to be 'good enough'.
ALL equipment is only Good Enough!
OR do you fly custom mfg Hughes, TRW... RC Rig?
If your not then you know I'm right!
> For that matter so does RC equipment. If it maintains control during the
> use that it is put to, then it is a good radio.
Exactly so you can quit your rant now. <G>
> > But you, in your infinate wisdom know more than they do, don't you???
>
> I never said any such thing.
> I also never claimed that AM was better than FM.
> You are claiming that FM is so much better than AM that someone would
> have to be stupid to fly AM. Did I get that right?
As usual, No.
I said AM is Better than FM. Not "so much better", not 5% better,
just better.
I never said how much better.
> The truth is, both AM and FM WORK.
And I've agreed with that all along.
So you can un knot your knickers now.
> > Now tell us what you fly, AM or FM???
>
> Depends on the radio I am using....
Rationalizations deleted.
But he never admitted to using AM more often or even as much as FM
on RC Airplanes. Ooooops!
> michael N6CHV (I also have a first phone, radar endorsement, so what)
No you don't, the P1 was combined with the P2 to form the PG (general)
commercial license. I see you don't know anymore about your license than
you do about RF Comm Equipment, which includes RC Equipment.
Well if you had a true understanding rather than just a Commercial License
(that you don't even know what class it really is) that you obviously don't
use almost daily, like I do... And had more hands on experience working
on, troubleshooting... Comm equipment. You Would Understand "So What".
Your continuing distancing RC equipment from Comm equipment to rationalize
points that you can not support further, also prove your ignorance.
Take care,
mike
Mike Dumas
Jim White wrote:
> this guy still doesn't get it.... transmitting voice and hearing
> "static" is not the same as FSK or keyed CW....
Of course its not the same as CW, the carrier remains there.
As for FSK, on a SSB signal its one thing,
BUT on a AM or FM signal its different, much closer to Voice.
But I disagree, so I don't get it? <VBG>
Fly AM Jim, Please!
mike
Phil Cole
Jim White wrote:
>
> Phil Cole <pcoleN...@net.com.invalid> wrote:
>
> >OK, I'll be first with the blowtorch..
>
> I'll only take issue with this one....
>
> >The difference between AM and FM is similar. AM
> >will degrade gracefully, and FM will work well until the
> >signal gets noisy, then go from good to bad in a hurry.
> >You will notice when comparing AM and FM broadcast reception.
> >Even allowing for the different propagation of MW and VHF,
> >AM stations just get weaker and weaker over many miles,
> >but FM goes from good to bad in a short distance.
> >
> >So, if the graceful degradation failure mode is desirable,
> >then AM is perferable to FM.
> >
>
> the graceful degradation you talk of, again, is primarily due to the
> different modes of propagation of VHF and LF signals.... not the mode
> of modulation...
Jim,
I was trying to relate to radios most people have experience with.
When I played at amateur radio, I was mostly on 2 m. AM, SSB, FM.
If I wanted to get somewhere without a repeater, SSB (or CW) was
the way to go.
Use a signal generator to see how much input signal
it took to get 20 dB s/n at the audio output.
Then see how much input takes to get 10 dB s/n, 5 dB, etc.
Of course FM can get a lot quieter than any AM once you
get nice strong signals. It basically does this by using
more spectrum. You can build an FM (voice) system that will
fit in a 3 kHz BW, but it will perform pretty much like AM.
--
Phil
Ton C. Jaspers
One remark though. I understand there is only one checsum for the
entire PCM frame. So, even if a single bit is in error the whole frame
has to be rejected if the checksum is the only criterion?
Ton
Jim White
>
>I said AM is Better than FM. Not "so much better", not 5% better,
> just better.
huh??? have you suddenly changed your stripes???
Jim White
>Amen.
>
>One remark though. I understand there is only one checsum for the
>entire PCM frame. So, even if a single bit is in error the whole frame
>
>has to be rejected if the checksum is the only criterion?
>
>Ton
you may be right.... I've never dissected the pulse stream used, but
everyone who has has said that the EC is very crude....
Jim White
>OK, I'll be first with the blowtorch..
I'll only take issue with this one....
>The difference between AM and FM is similar. AM
>will degrade gracefully, and FM will work well until the
>signal gets noisy, then go from good to bad in a hurry.
>You will notice when comparing AM and FM broadcast reception.
>Even allowing for the different propagation of MW and VHF,
>AM stations just get weaker and weaker over many miles,
>but FM goes from good to bad in a short distance.
>
>So, if the graceful degradation failure mode is desirable,
>then AM is perferable to FM.
>
the graceful degradation you talk of, again, is primarily due to the
different modes of propagation of VHF and LF signals.... not the mode
of modulation...
Jim White
Mike Dumas
Jim White wrote:
> Mike Dumas <mi...@vci.net> wrote:
> >
> >I said AM is Better than FM. Not "so much better", not 5% better,
> > just better.
>
> huh??? have you suddenly changed your stripes???
No.
I never said FM was "so much", lots, orders of magnitude... better.
Reread my posts. I Never Quantified the Degree!
Someone jumped to an assumption based upon my saying that FM was
better, and turned their argument into the position that I was saying
things that I did not.
Its a typical dynamic on NGs. That's why I try to form my assumptions
based on the other persons remark in the form of a question, to get
clarification.
BUT occasionally you run into a Michael Neverdosky type personality,
who when confronted with differing views, information...
Pole vaults to a conclusion and then defends it pseudo rationally,
mainly
emotionally, against perceived attacks using perceived arguments.
Tilting at Windmills... Quixotic.
He has this picture that everyone who disagrees with him, is polluted by
Ad Hype (based upon his continuing rant along this line). Ignoring that
some of us have been in the trenches for years. And He, Mr. Techno
Junkie (admitted in the PCM vs PPM drift) and his followers, are the
only truly enlightened. ;)
mike
Steve
This is what I have done, unless I am not understanding correctly. I check
the range with the PPM receiver. I get about 50 or so paces before the
control surfaces start to jitter, and will not respond correctly to my
transmitter commands. Then, the same plane, with the only difference being
the PCM receiver, will respond to the transmitter correctly out to
somewhere around 120+ paces before it goes into failsafe. Also, there are
no glitches detected by the installed BC6 glitch detector until that point.
To me, the effective range of the PPM is 50+ paces, and the effective range
of the PCM is 120+ paces. Regardless of what is behind this, error
correction, masking, or so on, I get a effective range increase of two fold
where the plane responds to my commands correctly. I can sit out at 120
paces and each and every control input is accurately reflected on the
control surfaces.
So, effectively, with a PPM receiver with the antenna down, I wouldn't fly
the PPM receiver out past 50 paces. With the antenna down, I wouldn't fly
the PCM receiver out past 120 paces. To me, that's 'effective' range.
That's assuming receivers can fly, and I would fly with my antenna down :-)
Steve
medi...@mindspring.com
RC web Site www.avcomproductions.com/planes.htm
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Jim White <jimw...@ij.net> wrote:
>
>at the risk of a flame war, might I suggest you consider the
>difference between "range" and "effective range" for lack of better
>terminology.... maybe the thing to do is range check your installation
>with PPM, then add the PCM for insurance.... the point being that the
>difference in range you are seeing is a result of the PCM rcvr
>"masking" the errors that the PPM rcvr is getting, not "eliminating"
>the errors.... I understand that under NORMAL conditions the
>difference is moot, but....
>
>maybe the mfg's should make switchable rcvrs (with the 8th channel?),
>so that we could easily determine the true integrity of the
>signal......
>
>Steve <Xmed...@mindspring.com> wrote:
>
>>I pushed off using PCM for cost, and failsafe issues, for quite some time.
>>Then, I keep noticing that those with the PCM receivers were range
>>checking their systems way way beyond all my PPM receivers. I decided
>>to test one. Same plane, same transmitter, only the receiver was swapped
>>out with a PCM receiver. I was out in the sticks on my next range check.
>>From around 50 paces on the 6 PPM receivers I have, to well over 113
>>paces with the PCM receiver. I put a PCM receiver in a new 38% Christen
>>Eagle I just acquired, and the same results. 121 Paces. I think I may be
>>sold on the range benefits of PCM.
>>
>>Steve
>
Ian Maclaughlin
Mike Dumas <mi...@vci.net> wrote:
<snipped much>
> So?
> You think RC equipment interference is different from all other forms
> of comm equipment just because its used for controlling a plane?
>
> It uses different RF???
>
> It uses different FM???
>
Mike-
Now you are asking the right question, even though you appear to have
intended it as rhetorical. Yes, RC does use different FM from most
forms of comm equipment. RC uses narrowband FSK, a most primitive form
of FM, i.e., binary keying sans any modulating audio frequency. With
due respect to your credentials and experience, which I have no reason
to question, I believe that if you would consider objectively the
significant differences between the narrowband FSK variant of FM used
by RC equipment vs. the more common FM systems of the wideband, large
modulation-index type that you are obviously quite familiar with and
have cited repeatedly, then you would discover the crux of the many
disputes with your assertions that have arisen in this interminable
thread.
Ian
San Diego
Sent via Deja.com http://www.deja.com/
Before you buy.
Phil Cole
similar tests.
In article <30ba4sgdrd1p632pk...@4ax.com>, Steve
* Sent from RemarQ http://www.remarq.com The Internet's Discussion Network *
Jim White
>
>This is what I have done, unless I am not understanding correctly. I check
>the range with the PPM receiver. I get about 50 or so paces before the
>control surfaces start to jitter, and will not respond correctly to my
>transmitter commands. Then, the same plane, with the only difference being
>the PCM receiver, will respond to the transmitter correctly out to
>somewhere around 120+ paces before it goes into failsafe. Also, there are
>no glitches detected by the installed BC6 glitch detector until that point.
the glitch detector is useless in the PCM situation.... until the rcvr
goes into fail safe, there will be NO glitches by definition....
>To me, the effective range of the PPM is 50+ paces, and the effective range
>of the PCM is 120+ paces. Regardless of what is behind this, error
>correction, masking, or so on, I get a effective range increase of two fold
I'm with you up to this point....
>where the plane responds to my commands correctly. I can sit out at 120
>paces and each and every control input is accurately reflected on the
>control surfaces.
you may think so, watching from 120' away, but some serious thought
will convince you that this is an impossibility... now, if you had
said "somewhat accurately".... or "sufficiently accurately"....
>So, effectively, with a PPM receiver with the antenna down, I wouldn't fly
>the PPM receiver out past 50 paces. With the antenna down, I wouldn't fly
>the PCM receiver out past 120 paces. To me, that's 'effective' range.
true....
>That's assuming receivers can fly, and I would fly with my antenna down :-)
let's hope not !!! :>)
Jim White
>
>
>Jim White wrote:
>
>> Mike Dumas <mi...@vci.net> wrote:
>> >
>> >I said AM is Better than FM. Not "so much better", not 5% better,
>> > just better.
>>
>> huh??? have you suddenly changed your stripes???
>
>No.
>
>I never said FM was "so much", lots, orders of magnitude... better.
> Reread my posts. I Never Quantified the Degree!
but in the above quote you say AM is better.... which is it???
>BUT occasionally you run into a Michael Neverdosky type personality,
> who when confronted with differing views, information...
> Pole vaults to a conclusion and then defends it pseudo rationally,
>mainly
> emotionally, against perceived attacks using perceived arguments.
> Tilting at Windmills... Quixotic.
>
many would say this sounds like you !!
Michael Neverdosky
> BUT occasionally you run into a Michael Neverdosky type personality,
Why are you attacking me BY NAME in the newsgroup?
By the way, you keep parroting the same stuff over and over, except now
you have made posts claiming FM is better and other posts that say AM
is better.
You are both an ass and apparently an idiot.
PLONK
Michael Neverdosky
Do not use my name in any post to any newsgroup on any subject.
Any use of my name or reference to me by name will be considered
slander and libel.
BTW I don't recall ever seeing the term "Michael Neverdosky" in
DSM III. Please quote the page number and the passage with a definition,
if there is such a thing.
Better yet, just shut up.
michael
Mike Dumas
Jim White wrote:
> but in the above quote you say AM is better.... which is it???
OK, I Dumb Thumbed that! <G>
> > Tilting at Windmills... Quixotic.
>
> many would say this sounds like you !!
And many would say you can only learn to fly with a trainer.
What many say doesn't bother me, nor does it make them right.
Many said the earth was flat too!
mike
Mike Dumas
Michael Neverdosky wrote:
> Mike Dumas wrote:
>
> > BUT occasionally you run into a Michael Neverdosky type personality,
>
> Why are you attacking me BY NAME in the newsgroup?
First of all I did not attack you, I told what I said and observed.
You posted by name.
You jumped to conclusions.
You claimed i'd said things that i did not.
You laid this Ad Hype argument on me and ignored what i said.
You admitted to being a Techno Geek.
I'm still considering which word the emphasis is on.
Why are you ashamed of the content of your posts?
Why are you ashamed of your actions?
Why are you Scared to be Named?
> By the way, you keep parroting the same stuff over and over, except now
> you have made posts claiming FM is better and other posts that say AM
> is better.
You jump on things to argue about with out first finding out the others
intention just to belittle them (more proof here in this post of yours),
and to continue your argument based upon your assumptions.
And you wonder why i doubt your supposed knowledge in this???
If you'd waited for a reply OR (Heaven Forbid) Asked if i was changing my
position or just made a typo before replying you could have found out the
Truth.
But you prefer to jump to conclusions and make claims based solely on
them,
not apparently caring what the Truth may be, as long as you apparently
feel superior
in your reply. You do know what Truth is don't you?
You never repeated yourself??? LOL
Oh, its OK for Michael Neverdosky to do anything as long as he isn't named
in the rebuttal, caught being closed minded, calls down others for doing
exactly
the same things he's doing...
> You are both an ass and apparently an idiot.
Your opinion, and considering the source, a rationalization that you can
live with.
Yes i can be an ass, keep up your misrepresenting what i've said, and lack
of
any intention to find out what i mean, and you'll find out what i can and
have done
online. But i reserve that for only the hard cases. So far your not more
than a small
annoyance. ;)
Name calling is for the weak minded, and the last resort of the looser of
an
argument, discussion...
BTW are you this way with everyone who disagrees with you?
Or just the ones with more experience?
mike
Mike Dumas
Michael Neverdosky wrote:
> btw
>
> Do not use my name in any post to any newsgroup on any subject.
> Any use of my name or reference to me by name will be considered
> slander and libel.
The gauntlet is thrown by Michael Neverdosky! <G>
You consider it anything you want. I couldn't care less what you consider.
I've played NG for years and I've argued with Lawyers and won.
So you (now a self proclaimed lawyer, judge, executioner...)
don't worry me in the least amount
As for slander and libel...
"You are both an ass and apparently an idiot." - Michael Neverdosky
...fits much more neatly into this category.
Gotcha!
Don't you hate it when your exact words are used against you?
BTW why didn't you take this childish post to private email???
OR do you like threatening people online?
Makes you feel big???
I'm willing to go to email anytime your ego (?) will let you.
> BTW I don't recall ever seeing the term "Michael Neverdosky" in
> DSM III. Please quote the page number and the passage with a definition,
> if there is such a thing.
Where did i say it was? Quote me! <BG>
More jumped to conclusions by Michael Neverdosky, just to bluster!
Oooh, Call your lawyer, I used your name. <G>
> Better yet, just shut up.
>
> michael
No!
Now that you've wanted to deny me my constitunally guaranteed right to
Freedom of Speech, I'll not shut up. I may even comment on your every post,
quoting your closed minded comments as proof.
But I won't, your not worth the effort. <G>
The next time you post to me, please bring a clue.
mike
BTW had you asked me not to use your name i would have freely complied.
But you are not going to order me around with idle threats and bad
attitude.
Now back to RC!!!
Mike Dumas
Ian Maclaughlin wrote:
> Mike-
> Now you are asking the right question, even though you appear to have
> intended it as rhetorical. Yes, RC does use different FM from most
> forms of comm equipment. RC uses narrowband FSK, a most primitive form
> of FM, i.e., binary keying sans any modulating audio frequency.
Finally someone with the ability to discuss this rather than posture and/or
troll.
Hi Ian.
Actually FM Broadcast in the 88-108mhz frequency range is the only (known
to me) service still using wideband FM.
Commercial, Ham, Marine, Cell Phones, Watercom, Comm Satellites... have all
gone to narrow band FM with a 5khz max freq deviation. Most new equipment
is
factory set to 4-4.5khz max but the RX discriminator doesn't usually ignore
the
signal until 6+ khz, depending on the circuitry used.
The only reason FM Broadcast is still 200khz spacing wideband is the FCC
regulates FM so its main harmonics fall within its own TX signal. Music at
higher
frequencies used have wider spaced harmonics, and there's the Stereo
SubCarrier...
and a lot of FM-B stations are using subcarriers to TX Musak, and other
signals
for added income to the station.
> With
> due respect to your credentials and experience, which I have no reason
> to question, I believe that if you would consider objectively
I'd love to IF someone would ever provide some facts, credible info...
but so far its not been that way.
> the
> significant differences between the narrowband FSK variant of FM used
> by RC equipment vs. the more common FM systems of the wideband, large
> modulation-index type that you are obviously quite familiar with and
> have cited repeatedly,
Narrow band cited repeatedly (except at the original onset of FM) by me.
But your apparently not up on the changes that have been going on.
> then you would discover the crux of the many
> disputes with your assertions that have arisen in this interminable
> thread.
Fine.
Where is the pertinent data online. (AM FSK vs FM FSK)
Exact site locations only, i'm not wasting hours, days... searching for
it.
I've flown FM with storms blowing up and only quit when the wind, rain...
made me. The lightening didn't bother the flying at all!
Lets hear some numbers on the total number of fields out in the boonies
where IMD, Capture... are not a problem for FM...
AND the number close to town where this is a problem.
IF were going to examine this lets use ALL the facts.
I have a feeling more fields are away from these problems.
You wanna win me over, present me with the Info to do that,
and the others stop their unsupported opinion spouting. <G>
BTW if the FM RXs aren't properly filtered for the tones...
Their bandpass is too wide, don't expect me to roll over and say
i'm wrong. Because the fact is, W/O proper filtering any signal is more
apt
to be interfered with. Ask Any Ham Radio Operator!
And yes I know digital (type) data is more apt to be interfered with than
audio
signals. BUT the reason for that is your comparing the human brain to one
IC...
make the Audio have to be Interpreted by one IC and lets see which mode is
screwed up the fastest! Apples and Oranges!!! <VBG>
Only when you compare Apples to Apples can you get to the Truth!
I tend to look beyond the surface info (unlike a Techno Geek) and look at
things
at a more level playing field and at greater depth. This discussion has a
depth and
breadth yet untouched on this NG (as far as i've seen).
This discussion of Human Brain VS IC deciphering (which is what some of this
actually boils down to Not AM-FM, FSK-Voice...) is Dumb!
Looking at only the data that supports someone's position won't solve
anything!
BTW since i went FM, I've never been hit!
mike
But then a self proclaimed expert says i'm an idiot, so what do i know? ;)
Jim White
>And yes I know digital (type) data is more apt to be interfered with than
>audio
> signals.
here's where I keep tripping over your logic.... this discussion keeps
mixing and blending issues without keeping the threads straight....
there is the AM vs FM issue, then there is a sub text of modulation
schemes... many of your assertions involve comparing "analog"
modulation with "digital", which is tough to relate to voice/music vs.
FSK time base vs. FSK PCM.... you seem to equate analog to the first,
and digital to the last, while not addressing the middle one which is
the most common, PPM.... acceptable performance in the first,
voice/music, is clearly influenced by human perceptions... "static"
over my Pink Floyd or Rush Limbaugh (g) is not well tolerated when it
obscures a word here or there.... the nature of this very analog
transmission requires faithful reproduction of a continuously varying
modulation signal with many discrete levels... FSK, on the other hand,
is a Bang-Bang signal with only two levels... sufficient
amplification, meaning driving the amps into clipping if possible,
ensures that the signal contains predominately only the two levels of
intelligence being transmitted... be it carrier off/on as in AM FSK,
or F1/F2 as in FM FSK... in a properly adjusted AM FSK system, we can
see amplitude disturbances of +/20% or more that will never make it to
the decoder but would render voice/music un-intelligeble....
obviously, these would not affect an FM system either.... as for
extremely large amplitude variations which do cause the control link
to be interfered with, some of these will affect the FM system as
well, after all, a drop out of the carrier will convey no intelligence
regardless of modulation type... that's modulation type, not encoding
scheme... and slight glitching often goes quite unnoticed... ref the
surprised looks the first time someone uses a glitch counter....
point is, under very adverse conditions (end of range, thunderstorms,
mistuned equip., malicious jammers), in the scenarios an RC system is
most likely to be exposed to, FM FSK may be slightly better than AM
FSK in rejection of amplitude variation induced interference... under
average to normal conditions, which will account for probably 98% of
our flying time, the difference is moot....
>BUT the reason for that is your comparing the human brain to one
>IC...
> make the Audio have to be Interpreted by one IC and lets see which mode is
> screwed up the fastest! Apples and Oranges!!! <VBG>
you've made my point!
>Only when you compare Apples to Apples can you get to the Truth!
how true, how true...
Mike Dumas
Jim White wrote:
> Mike Dumas <mi...@vci.net> wrote:
> >And yes I know digital (type) data is more apt to be interfered with than
> >audio
> > signals.
>
> here's where I keep tripping over your logic.... this discussion keeps
> mixing and blending issues without keeping the threads straight....
Because to get a true answer, its more complicated than One issue.
> there is the AM vs FM issue,
The issue i commented upon...
then Michael Neverdosky (the guy who claims he's going to sue me
for using his name in other posts) and you (?) started the FSK position,
"mixing and blending issues" as you call it.
> then there is a sub text of modulation
> schemes...
No, there's the Thread subject of modulation schemes, "AM vs FM".
See the subject line above. Voice, Music, FSK... are all putting audio
tones on a modulation scheme, AM, FM, SSB (a true AM subtype)...
I think where were parting ways is i'm looking at the complete
radio link, and your looking at the end results, usually limited to the
RX's abilities.
AM suffers noise problems that FM does not...
If a $50 RX doesn't have proper filtering its not the issue IMO.
That falls under the category of RX design, NOT Modulating with
AM or FM.
As for the PPM vs PCM... ?
I don't know.
I do know that as long as PPM is Good Enough, as its always been
for me, thats what i'll use. And i'm leary of the lockout of RX signals
with PCM. I've landed radio crippled planes (Hit Hard w/interference,
Fractured Xtal...) safely (to people if not the plane) with PPMs eratic
control
BECAUSE I still had a little control, where PCM would have rejected the
whole thing.
BTW the fractured Xtal incident was someone elses plane who didn't properly
range test it after a crash, and the Hit Hard was my First Radio on the CB band
flying next to a interstate, while landing.
> many of your assertions involve comparing "analog"
> modulation with "digital", which is tough to relate to voice/music vs.
> FSK time base vs. FSK PCM....
Digital is what FSK is...
Digital, a 2 state number system (0,1), 2 tones (Mark, Pulse)...
FSK is therefore a Digital type of intelligence placed upon a AM or FM
TX signal. The RX used in this signal normally uses Voice components
like detectors (for FM) that pass about 6khz of frequencies on either side
of the carrier, rather than being specially designed to home in and only
pass the 2 tones. A RX Problem.
I know the FCC classifies it differently, they have to know whats on the
modulation type.
> you seem to equate analog to the first,
> and digital to the last, while not addressing the middle one which is
> the most common, PPM....
PPM is still a Digital mode of modulating the AM/FM carrier...
2 tones...
Just because the information is time based (pulse width) and infinitely
variable (within its range) does not magically make it non digital.
True the end movement (servo output) is pure analogue,
but the radio link is digital.
> acceptable performance in the first,
> voice/music, is clearly influenced by human perceptions...
Just like i stated yesterday to Ian...
> "static"
> over my Pink Floyd or Rush Limbaugh (g) is not well tolerated when it
> obscures a word here or there....
But the data is still transferred with the brain, upset <G>, but still using its
Super
Duper analytical abilities (makes a Cray III look like a 4 function
calculator).
to ignore interference and pull out the data.
> the nature of this very analog
> transmission requires faithful reproduction of a continuously varying
> modulation signal with many discrete levels...
Nope, the Brain fills in more than you think, or know!
Ever have a conversation with some background static on a radio, cell phone...
and understand every word?
A Fax on that line (digital, fsk...) would turn out garbage.
> FSK, on the other hand,
> is a Bang-Bang signal with only two levels... sufficient
> amplification, meaning driving the amps into clipping if possible,
> ensures that the signal contains predominately only the two levels of
> intelligence being transmitted...
Not when driven to clipping with FM!
The clipping is performed at the RX so when clipping occurs the signal is
completely gone.
Crank a 2 way radios TX up and watch a service monitor while listening to
a RX at the same time to confirm this.
Overdriven on AM causes distortion...
AM is not really Amplitude Modulated, the carrier is constant and 2 side bands
are generated, but to an oscilloscope it appears that the amplitude of the
carrier
is changing. When the side bands swing too far, past the carrier frequency...
Oooops!
Once again, FSK shoots craps, but the brain still hears words.
> be it carrier off/on as in AM FSK,
WRONG! (i think you dumb thumbed this time, it happens to us all <G>)
Carrier on/off is CW (for morse code), not FSK.
FSK means Frequency Shift Keying...
the tone (frequency) changes, you do Not unkey and rekey the TX.
FSK is constantly transmitting a Mark OR pulse tone, except in AMTOR and
PACKET which use error correction schemes that listen after so much is sent
to get a verification back from the RX station that that much data was received
correctly, if not its resent.
> or F1/F2 as in FM FSK... in a properly adjusted AM FSK system, we can
> see amplitude disturbances of +/20% or more that will never make it to
> the decoder but would render voice/music un-intelligeble....
Because Good FSK RX's can use only One Tone to RX the signal,
they assume that absence of that tone = the other tones presence!
And one tone (frequency) Voice or Music is unintelligible
These RX stations use Extreme Audio filtering for both tones...
Does any RC RX do that? None that I know of.
Its the same principal as CW...
with a Very Narrow audio filter you (your brain) can decipher code
in a mish mash of noise and other signals...
BUT computerized RX can not.
> obviously, these would not affect an FM system either.... as for
> extremely large amplitude variations which do cause the control link
> to be interfered with, some of these will affect the FM system as
> well, after all, a drop out of the carrier will convey no intelligence
> regardless of modulation type...
Regardless if its AM or FM?
> that's modulation type,
Nope, increase the AM signal to 120% modulation and it distorts and
you loose its control too.
> not encoding
> scheme...
That's what i've been saying, voice, music, fsk...
are encoding schemes not types of modulation.
AM and FM are types of modulation.
> and slight glitching often goes quite unnoticed... ref the
> surprised looks the first time someone uses a glitch counter....
Very true.
> point is, under very adverse conditions (end of range, thunderstorms,
> mistuned equip., malicious jammers), in the scenarios an RC system is
> most likely to be exposed to, FM FSK may be slightly better than AM
> FSK in rejection of amplitude variation induced interference...
And thanks for admitting what i originally said...
FM is better than AM. <G>
The other problems are RX design based...
> under
> average to normal conditions, which will account for probably 98% of
> our flying time, the difference is moot....
I never said otherwise under normal conditions.
Under normal conditions Who Cares?
Its these problem conditions that are the worry, Ergo my position.
> >BUT the reason for that is your comparing the human brain to one
> >IC...
> > make the Audio have to be Interpreted by one IC and lets see which mode is
> > screwed up the fastest! Apples and Oranges!!! <VBG>
>
> you've made my point!
As you've made mine!
> >Only when you compare Apples to Apples can you get to the Truth!
>
> how true, how true...
Well, i'm glad to know your not another
Michael (threats and name calling) Neverdosky.
Take care Jim.
mike
Steve
>
>the glitch detector is useless in the PCM situation.... until the rcvr
>goes into fail safe, there will be NO glitches by definition....
>
Yes, I understand this. Unfortunately, that's the way it was designed.
At least when I fly, I know it hasn't gone into failsafe when I check the
glitch detector and its zero.
>
>>where the plane responds to my commands correctly. I can sit out at 120
>>paces and each and every control input is accurately reflected on the
>>control surfaces.
>
>you may think so, watching from 120' away, but some serious thought
>will convince you that this is an impossibility... now, if you had
>said "somewhat accurately".... or "sufficiently accurately"....
>
Actually, I know so. I don't watch from 120 paces, as that would be useless
for the reasons you mentioned. I tend to fly with a particular person all
the time, and we assist each other with our range checks. I can guarantee
that they control surfaces respond as directed, accurately, without any
jitters.
>>So, effectively, with a PPM receiver with the antenna down, I wouldn't fly
>>the PPM receiver out past 50 paces. With the antenna down, I wouldn't fly
>>the PCM receiver out past 120 paces. To me, that's 'effective' range.
>
>true....
>
>>That's assuming receivers can fly, and I would fly with my antenna down :-)
>
>let's hope not !!! :>)
>
:-)
bills...@my-deja.com
>often goes quite unnoticed... ref the surprised looks the first time
Could you share your experiences with glitch counters? Also where might
these be purchased? And is the frequency of checking adjustable? I
assume that if every frame were evaluated the error rate would be very
high.
Thanks.
Bill Stanley
In article <2odi4s8sbnge76nnv...@4ax.com>,
Jim White <jimw...@ij.net> wrote:
> Mike Dumas <mi...@vci.net> wrote:
> >And yes I know digital (type) data is more apt to be interfered with
than
> >audio
> > signals.
>
> here's where I keep tripping over your logic.... this discussion keeps
> mixing and blending issues without keeping the threads straight....
> there is the AM vs FM issue, then there is a sub text of modulation
> schemes... many of your assertions involve comparing "analog"
> modulation with "digital", which is tough to relate to voice/music vs.
> FSK time base vs. FSK PCM.... you seem to equate analog to the first,
> and digital to the last, while not addressing the middle one which is
> the most common, PPM.... acceptable performance in the first,
> voice/music, is clearly influenced by human perceptions... "static"
> over my Pink Floyd or Rush Limbaugh (g) is not well tolerated when it
> obscures a word here or there.... the nature of this very analog
> transmission requires faithful reproduction of a continuously varying
> modulation signal with many discrete levels... FSK, on the other hand,
> is a Bang-Bang signal with only two levels... sufficient
> amplification, meaning driving the amps into clipping if possible,
> ensures that the signal contains predominately only the two levels of
> intelligence being transmitted... be it carrier off/on as in AM FSK,
> or F1/F2 as in FM FSK... in a properly adjusted AM FSK system, we can
> see amplitude disturbances of +/20% or more that will never make it to
> the decoder but would render voice/music un-intelligeble....
> obviously, these would not affect an FM system either.... as for
> extremely large amplitude variations which do cause the control link
> to be interfered with, some of these will affect the FM system as
> well, after all, a drop out of the carrier will convey no intelligence
> regardless of modulation type... that's modulation type, not encoding
> scheme... and slight glitching often goes quite unnoticed... ref the
> surprised looks the first time someone uses a glitch counter....
>
> point is, under very adverse conditions (end of range, thunderstorms,
> mistuned equip., malicious jammers), in the scenarios an RC system is
> most likely to be exposed to, FM FSK may be slightly better than AM
> FSK in rejection of amplitude variation induced interference... under
> average to normal conditions, which will account for probably 98% of
> our flying time, the difference is moot....
>
> >BUT the reason for that is your comparing the human brain to one
> >IC...
> > make the Audio have to be Interpreted by one IC and lets see which
mode is
> > screwed up the fastest! Apples and Oranges!!! <VBG>
>
> you've made my point!
>
> >Only when you compare Apples to Apples can you get to the Truth!
>
> how true, how true...
>
> Jim White
> AMA 2466
> WB2WOY
> WPMPA/BCF/PFC
> SouthShoreSoftware
> Treasure Island,
Jim White
I detect a distinct softening from your original stance, and would
like to suggest we agree to disagree on some things and agree on
others...... your points on PCM are well taken....
Mike Dumas <mi...@vci.net> wrote:
Jim White
AMA 2466
WB2WOY
WPMPA/BCF/PFC
SouthShoreSoftware
Treasure Island, FL
Jim White
>>>where the plane responds to my commands correctly. I can sit out at 120
>>>paces and each and every control input is accurately reflected on the
>>>control surfaces.
>>
>>you may think so, watching from 120' away, but some serious thought
>>will convince you that this is an impossibility... now, if you had
>>said "somewhat accurately".... or "sufficiently accurately"....
>>
>Actually, I know so. I don't watch from 120 paces, as that would be useless
>for the reasons you mentioned. I tend to fly with a particular person all
>the time, and we assist each other with our range checks. I can guarantee
>that they control surfaces respond as directed, accurately, without any
>jitters.
no, you won't get jitters.... that's a PPM thing.... you'll get
sluggish or "un-smooth" movement, kinda like when the Indy cars go
under an overpass and the onboard camera image kinda stutters... think
about it.... if you are at the point where the RF signal is
compromised, and the PCM error detection comes into play, the best it
can do is put you into momentary "holds".... it can't re-construct
the signal it didn't receive....
Steve
Jim,
I understand what you are saying completely. All I am saying is that the
controls act 100% normal from 120 paces under the watchful eye of two
knowledgable and experienced flyers. Pete knows how my planes reacts to
full control sticks. I start a standard set of control movement when I
start walking out, and he mimics them back to me with hand signals. He
would notice a difference in speed, since I use the same pattern each time
I test the controls while I take my walk, and I start right next to the
plane and don't stop until I run out of range. And there is no change when
I am out to about 90% of the full distance. The last 10% is where I get
glitches, and goes into hold occasionally, then finally goes unresponsive
as I go further out. There are no hints of any problem until I am well over
100 paces.
The same is true when we range check his plane. We run through the same
procedure. He also runs a PCM with airtronics 94258s. I see no change in
his controls as he moves out from 1 pace to 100+ paces. Same speed end to
end, full control, same pattern repeated all the way out. If there was a
drastic or very noticeable difference, one of us would have picked it up by
now. All I see is normal movements all the way out, until he gets to the
end of his range, then the glitch detector starts counting and he goes
unresponsive.
Now, I know the signal isn't 100% behind the scenes, but the controls are
not reflecting this for what ever the reason, and there has to be one. So
it may be slower, but it not noticeable enough to detect it even when we
are looking for any changes during a range check. If its slower, its very
subtle indeed.
Further, with the PPM, I start getting jitters around 35% or so of the PCM
range, and the controls are totally unresponsive at about 50%. With PCM, I
get twice the range, under control, before it gets totally unresponsive. So
this all goes back to effective range, which is what I was commenting on in
the first place. If I set a threshold of controllability where I would fee
comfortable that my plane will be in control 100% of the time, and use that
threshold to measure PPM and PCM, the PCM is easily double that of the PPM.
This is with the antennas down. I would expect about the same ratio once
the antenna are extended (ie, same radio and all).
In summary, this approximates what I see on my planes. Petes places are
very similar, but the distances might vary.
30-40 paces - PPM jitters start, but full control
50-60 paces - PPM receiver/servos go unresponsive
110 pages - PCM still 'appears' 100% normal
120 pages - PCM goes unresponsive
I would fly my PCM plane to 100 paces with the antenna down with any
concerns. I would loose my PPM plane at 50 paces. Thats what I mean when I
say effective range. Whatever magic they are doing during those last 60
pages, they are doing very well, because it doesn't show up any problems in
the planes controls.
Steve
Jim White
>Further, with the PPM, I start getting jitters around 35% or so of the PCM
>range, and the controls are totally unresponsive at about 50%.
this would indicate an inferior design PPM recvr or, if similar
design, one that is faulty....
Steve
>Steve <Xmed...@mindspring.com> wrote:
>>Further, with the PPM, I start getting jitters around 35% or so of the PCM
>>range, and the controls are totally unresponsive at about 50%.
>>Steve
>
>this would indicate an inferior design PPM recvr or, if similar
>design, one that is faulty....
>
This doesn't make sense. All my PPM receivers range check about the same.
50 paces or so, which is at tad over what the manuals, and those here in
the newsgroup, say you should expect (100 feet +). I also notice that those
that fly at the field I fly at seem to range check more or less about the
same. Usually, half way from the pits to the tree line. The only people I
see talking long walks out to the tree line are those that are flying with
PCM. This is one of the reasons I bought my first PCM receiver. I had to
find out for myself, and wanted to make sure it wasn't just a JR thing :-)
It wasn't.
I suppose this could drag on and on. However, I am quite happy knowing that
at double the normal PPM distance, when I give it full left aileron, it
goes full left aileron, just as if I was standing right next to it. I am
also satisfied with my testing methodology which shows that the PCM
receiver doubled my 'effective' range while retaining complete control. I
walk twice as far with my range checks that anyone else at our field with
PPM receivers. The other 4 people that I know with PCM at our field also
seem to meet at the tree line.
Technically, I am not knowledgable enough with the PCM mechanics to
decipher why this is happening. However, I know it is, and can reproduce it
at will, as many others has attested already.
Works for me, and has been for quite some time now.
Ian Maclaughlin
Mike Dumas <mi...@vci.net> wrote:
<much snipped>
> Where is the pertinent data online. (AM FSK vs FM FSK)
> Exact site locations only, i'm not wasting hours, days... searching
for
> it.
Mike-
In comparing modulation modes for R/C, I think it is CW vs FSK. No
matter, we can talk AM vs FM, as the modes we use can be considered as
devolved from these. I don't have a web site to refer you to, but
perhaps I can lead you through a brief comparative analysis, if my
memory doesn't glitch too badly. Let's pass over a lot of the
preliminaries and derivations and start with the relationship:
(S/N)fm = 3 B^2(S/N)am,
where (S/N)am and (S/N)fm are the output signal to noise ratios for the
AM and FM cases, respectively, and B is the modulation index. It has
been assumed, in order for the relationship to be valid, that the AM
signal is 100 percent modulated.
Considering your experience, I think it will be familiar to you. I
learned it decades ago (never mind how many) as an undergraduate EE
major, and probably haven't fetched it from archival memory since those
days until now!
From this simple equation, it is obvious that for a large
modulation index (>>1), we can increase S/N greatly over the AM case,
and this underpins the widely recognized advantage of FM. Obviously
this takes bandwidth, as modulation index is the ratio of the bandpass
of the channel to the frequency deviation of the modulating signal.
Notice that when B is reduced to 1/(3^(1/2)), or about 0.6, the S/N
ratio for the FM signal is the same as for the AM case. This is the
transition value that defines the threshold between wideband and
narrowband FM in the sense I intended in a previous post. To visualize
the situation, it may help to picture a frequency domain plot of a
narrowband FM signal (by the above definition), which more closely
resembles an AM waveform than its wideband counterpart. That is, there
are only first upper and lower sidebands present. The signals are
different, despite the missing higher order sidebands that are familiar
in a wideband FM signal, but only in phase relationship between the
sidebands and the carrier. Nothing really to account for a difference
in performance against noise. Just the fact that the signaling
bandwidth for the narrowband FM case and the AM case is the same, i.e.
2X the modulating frequency, provides a strong intuitive hint that the
signal to noise power ratios will also be the same. It may be too bold
to state it as axiomatic, but I am unaware of any noise-improvement
scheme for information transmission that does not exact a cost in terms
of increased bandwidth.
There is also the threshold effect to consider as a limitation on
the noise-improvement of FM, but I think in general that we rely on a
fairly high carrier to noise power ratio (more than about 10-15 dB) in
our R/C applications, so it is probably not germane to this discussion.
As for the economic advantage of FM, I think the handwriting is on
the wall. Pete Waters mentioned in his Dec RC Report column that Hitec
is dropping their excellent dual conversion AM Rx from the product
line. It has 105 discrete components, and is thus far more labor
intensive to produce than FM Rx's that use integrated packages
developed for other, high volume markets. The AM vs FM discussion
becomes moot when cost outweighs any possible technical merits of one
mode over the other for our R/C purposes.
If you want to discuss this subject any further, I'd enjoy it, but
let's take it to Email. I try to avoid the techno-geek stuff in this
forum when it gets beyond the lay interest level. I do enjoy the
topic - I've fielded adaptive digital processors that effectively deal
with 'intelligent' noise sources having in-band power advantages of
many orders of magnitude - Nyquist be damned.
Ian
San Diego