Aviation Radio Freq.
pro...@eldp.epfl.ch
I wish to buy a short wave radio, a Grundig Yachtboy 500, that a
advertisement in a US magazine claims can tune into the aviation band.
However the retailers here in Switzerland, who are not very knowlegable,
claim it doesn't. This could be because it is unlawful to listen or is
there a technical difference.
My question is, what are the aviation freq. in the US and what type of
transmission, ie is it AM, FM or SSB etc? I am interested in the US freq.
as we are moving there (Palo ALto) in the future.
Thanks in adavance
Michael Proctor
scha...@notis.com
In article <proctor-1409...@mac-247-107.cern.ch>,
Michael,
According to my scanner handbook the aviation raadio is allocated the
108.00MHz to 136.975 MHz. The segment from 108.00 MHz to 118.00 MHz is assigned
to air navigation aids (navaids) and the rest is for voice communication.
There is probably a high degree of complexity involved in suballocations of
frequencies for specific types of navaids but my AIM/FAR 1994 is at home. THese
frequencies should be international and not specific to the US. It's not SSB
but I can't recall if it's AM or FM.
If you are comming to the state for an extended period of time you may want to
wait to by a radio/scanner here.
Ben Schapiro
scha...@notis.com
Standard disclaimer, Ameritech and I do not speak for each other.
Julian Scarfe
pro...@eldp.epfl.ch wrote:
Whether the magazine is telling an outright lie or not depends on how you
stretch the definitions of "short wave" and "aviation band".
The most interesting segment of the spectrum from a civil aviation point
of view is the VHF range 118 MHz to 137 MHz; the transmissions are
amplitude modulated (A3E). These frequencies are used worldwide for
communication between Air Traffic Control and aircraft, except over long
stretches of unpopulated surface (e.g. the North Atlantic) where HF is
used (J3E, which, correct me if I'm wrong, is SSB).
The only aviation related (voice) info I've been abe to get with a "short
wave" receiver in the UK is the RAF Met broadcast, which is not without
its uses but is not going to give you much insight into the way ATC works!
Save your Francs unless it does AM VHF in the appropriate range.
Julian Scarfe
ja...@cus.cam.ac.uk
Gary Sims
>
>In article <proctor-1409...@mac-247-107.cern.ch>,
><pro...@eldp.epfl.ch> writes:
>> My question is, what are the aviation freq. in the US and what type of
>> transmission, ie is it AM, FM or SSB etc? I am interested in the US freq.
> According to my scanner handbook the aviation raadio is allocated the
>108.00MHz to 136.975 MHz. The segment from 108.00 MHz to 118.00 MHz is
> assigned
>to air navigation aids (navaids) and the rest is for voice communication.
>but I can't recall if it's AM or FM.
It's AM. If you are interested in military frequencies, they are
between 225 and 400 MHz (plus or minus some change), also AM. Oceanic is
HF SSB (upper), I don't have the freqs handy.
--
-----------------------------------------------------------------------------
Gary W. Sims, P.E. E-Mail: gs...@bobcat.ece.ohiou.edu
Avionics Engineering Center Voice: (614) 593-1519
Ohio University, Athens, Ohio 45701 FAX: (614) 593-1604
mike_w...@email.mot.com
snip
>
> frequencies should be international and not specific to the US.
It's not SSB
>
> but I can't recall if it's AM or FM.
>
> If you are comming to the state for an extended period of time you
may want to
>
> wait to by a radio/scanner here.
>
> Ben Schapiro
> scha...@notis.com
> Standard disclaimer, Ameritech and I do not speak for each other.
It's AM. This can be the tough part. Most VHF radios/scanners
demodulate FM only so they exclude the aircraft spectrum. My Icom
IC24 Ham Radio handheld demodulates AM in the aircraft spectrum, but
the audio quality is terrible. I would want to a radio out first, or
at least ensure that it has a satisfaction or your money back clause.
Regards, Woody
AA7HN _
******************************* <_)
* Mike Woodward * o ______/|__ |
* Mechanical Engineer * __\___....---~ /| ~~\|
* Motorola, Government & * | ____/_|_ _|>
* Systems Technology Group * |~~/~~~---...__/ / |/~~~ |
* Multichip Modules/Systems * |_/ --===OOOOOO= |
* Scottsdale, Arizona *
* mike_w...@email.mot.com * YeeeeeeHaaaaaaa!
*******************************
These opinions are my own...not Motorola's!
Alexander Kleinberg
> In article <proctor-1409...@mac-247-107.cern.ch>,
> pro...@eldp.epfl.ch wrote:
>
> > Hi,
> > I wish to buy a short wave radio, a Grundig Yachtboy 500, that a
> > advertisement in a US magazine claims can tune into the aviation band.
> > However the retailers here in Switzerland, who are not very knowlegable,
> > claim it doesn't. This could be because it is unlawful to listen or is
> > there a technical difference.
> > My question is, what are the aviation freq. in the US and what type of
> > transmission, ie is it AM, FM or SSB etc? I am interested in the US freq.
> > as we are moving there (Palo ALto) in the future.
Incidentally, when you move to Palo Alto, Palo Alto Airport's frequencies
are:
Tower 118.6, Ground 125.0, ATIS 120.6.
Bay Approach/Departure has, depending on the quadrant, 135.65, 135.1,
120.1, 135.4, 121.3, 135.2, 135.45 and some others. The Airport Shoppe at
PAO sells transceivers, aviation band scanners, and other information on
aviation radio communications. If you want to play it safe, you might wait
to buy the scanner until you arrive in the US. However, worldwide
frequency bands should be the same.
--
Alexander Kleinberg
Brown University
st00...@brownvm.brown.edu
PP-ASEL, Palo Alto Flying Club
Alex Schwassmann
ja...@cus.cam.ac.uk (julian scarfe) wrote in article
<jas12-15099...@131.111.200.3> concerning "re: aviation radio freq.":
js> The only aviation related (voice) info I've been abe to get with a "short
js> wave" receiver in the UK is the RAF Met broadcast, which is not without
js> its uses but is not going to give you much insight into the way ATC works!
But then again, if you don't know how ATC works beforehand, the
short transmissions (which aren't exactly proper English either)
are probably not going to make much sense anyway. And if you're
not living near an airport, chances are you will only get the
pilots' replies, which makes even less sense.
... Alex
Alexander Schwaszmann // EMail: ALEX_SCH...@aworld.aworld.de
my personal opinions ... \X/ ATC Germany - EDDL APP/TWR
Julian Scarfe
> The most interesting segment of the spectrum from a civil aviation point
> of view is the VHF range 118 MHz to 137 MHz; the transmissions are
> amplitude modulated (A3E).
Someone subsequently asked me *why* they are AM not FM (after all,
commercial broadcast VHF in the 88 to 10? MHz range is FM). Explanations
please?
Thanks
Julian Scarfe
ja...@cus.cam.ac.uk
Jay Maynard
Julian Scarfe <ja...@cus.cam.ac.uk> wrote:
>Someone subsequently asked me *why* they are AM not FM (after all,
>commercial broadcast VHF in the 88 to 10? MHz range is FM). Explanations
>please?
Money.
It would cost billions of dollars to replace all the AM radios in the
aircraft of the world with FM. Pilots would reject the idea because they
would see no good in it.
Another reason is the FM capture effect: While that's a Good Thing for most
uses, it's a bug in the aviation arena, where both pilots and controllers
need to know that a transmission was blocked, fully or partially, by another
signal.
--
Jay Maynard, EMT-P, K5ZC, PP-ASEL | Never ascribe to malice that which can
jmay...@admin5.hsc.uth.tmc.edu | adequately be explained by stupidity.
The US Constitution: 1789-1994. RIP.
mor...@ipers1.e-technik.uni-stuttgart.de
The readability of signals drops with FM quite dramaticaly with signal
strength, when you get to the point when the harsh noise comes in.
AM is more forgiving there similar to ssb. (compare to terestial
and satellite TV)
With AM you will allways know if two stations are talking on top if each
other. Of cause SSB would be even better there, but it is too fiddly
to tune, specially in emergency situations. Experiments with suppressed
carriers were not quite successful to my knowledge.
73, Moritz DL5UH
Paul H. Bock
>There are essentially two reasons:
>The readability of signals drops with FM quite dramaticaly with signal
>strength, when you get to the point when the harsh noise comes in.
This is a little misleading. FM holds it's "communicability"
*very well* with decreasing signal strength, and in fact drops off
to unintelligible only after a certain point is reached (the so-
called "threshholding effect"). AM drops off gradually with decreasing
signal strngth, and unfortunately the carrier can often be identified
as present when the modulation is unintelligible. With SSB, the
modulation is readable right down very close to the noise level (there
being no carrier).
For AM, a 7 dB signal plus noise to noise ratio is generally
regarded as equivalent to a 3 dB SNR for SSB. Comparing FM to
either AM or SSB is sort of "apples to oranges" because of the
threshhold effect, but it usually occurs at about the equivalent
of 6 dB SNR; however, this varies with such things as modulation
index, so is too complex to elaborate here.
>With AM you will allways know if two stations are talking on top if each
>other. Of cause SSB would be even better there, but it is too fiddly
>to tune, specially in emergency situations. Experiments with suppressed
>carriers were not quite successful to my knowledge.
With modern technology, channelized SSB could easily be made
both stable and reliable with no "tuning" necessary. The military
has used it for decades.
I think that the real reason AM is still used is the cost of
converting to SSB. Every aircraft radio in the world would have to
be replaced, and there could be no "transition" period because AM
and SSB are incompatible if you try to use them together; SSB
requires that a beat frequency oscillator be "on" in the receiver,
which causes AM to sound like one big squeal. Conversely, SSB
sounds like a bunch of ducks quacking on a an AM receiver (no BFO).
Similarly, AM and FM are also totally incompatible when used
on the same frequency (disregarding "slope detection" of FM on an AM
receiver, which doesn't really count).
Just my two cents.
*******************************************************************
_____
_________|_________ Paul H. Bock, Jr. Principal Systems Engineer
\(*)/ E-Systems/Melpar (703) 560-5000 x2062
o/ o \o Internet: pb...@melpar.esys.com
"Flying is the second-greatest activity
known to man; landing is the first."
*******************************************************************
Alan Bloom
: In article <jas12-19099...@131.111.200.1>,
: Julian Scarfe <ja...@cus.cam.ac.uk> wrote:
: >Someone subsequently asked me *why* they are AM not FM
: Another reason is the FM capture effect
Another reason is that AM has a small signal/noise advantage over FM
for weak signals. FM is better above a certain signal level threshold,
but AM is better for signals near the noise level.
AL N1AL
Andrew J. Milan
Bock) wrote:
SSB
> requires that a beat frequency oscillator be "on" in the receiver,
> which causes AM to sound like one big squeal. Conversely, SSB
> sounds like a bunch of ducks quacking on a an AM receiver (no BFO).
>
> Similarly, AM and FM are also totally incompatible when used
> on the same frequency (disregarding "slope detection" of FM on an AM
> receiver, which doesn't really count).
>
This brings up another question. While most ADF receivers I've seen have a
BFO setting, it's never used. What is its purpose? Are there SSB
transmitters out there that can be used? Where are they? Is there a list?
Are they of any use? Is this a fallback to an earlier era of equipment
that is no longere used/useful?
Thanks.
--
Ace
Mark A. Matthews
Andrew J. Milan <ajm...@msmacab.remnet.ab.com> wrote:
>This brings up another question. While most ADF receivers I've seen have a
>BFO setting, it's never used. What is its purpose? Are there SSB
>transmitters out there that can be used? Where are they? Is there a list?
> Are they of any use? Is this a fallback to an earlier era of equipment
>that is no longere used/useful?
Somewhere in the world, more common a few decades ago...
Some non-direction beacons identify with on-off keying of the carrier (A1
modulation). The BFO provides a beat note making it easier to identify
the station. Without the BFO, the sound heard from the ADF is a change in
the background static, with a bit of popping at the switch transitions.
The remaining question is, can anyone cite any operating examples of such
beacons?
-Mark
Roy Smith
> It would cost billions of dollars to replace all the AM radios in the
> aircraft of the world with FM. Pilots would reject the idea because they
> would see no good in it.
Yeah, but why was it AM in the first place? Did they not have FM when they
started putting VHF radios in airplanes? Or were FM sets just more complex
to build, or heavier, or more power-hungry, or something like that?
> Another reason is the FM capture effect: While that's a Good Thing for most
> uses, it's a bug in the aviation arena, where both pilots and controllers
> need to know that a transmission was blocked, fully or partially, by another
> signal.
I'm not sure I follow that logic. Isn't the protocol "if you hear an
acknowledgement, you know your transmission got through, else assume it
didn't"? How would capture effect change that?
--
Roy Smith <r...@nyu.edu>
Hippocrates Project, Department of Microbiology, Coles 202
NYU School of Medicine, 550 First Avenue, New York, NY 10016
"This never happened to Bart Simpson."
Jim Bromley, W5GYJ
>>> Someone subsequently asked me *why* they are AM not FM
>> Jay Maynard (jmay...@nyx10.cs.du.edu) wrote:
>> Another reason is the FM capture effect
> Alan Bloom <al...@hpnmarb.sr.hp.com> wrote:
> Another reason is that AM has a small signal/noise advantage over FM
> for weak signals. FM is better above a certain signal level threshold,
> but AM is better for signals near the noise level.
I think the real reason is historical. HF aircraft radio was
AM, so when VHF operation started in WWII, AM was the natural
choice over the still experimental FM. By the time the land
mobile services adopted FM, aircraft VHF was well-deployed and
the standard was set.
Jim Bromley, W5GYJ <jbro...@sedona.intel.com>
Tom 'CaptZoom' Scarince
cheap FM radio to the top of the scale?
-------------------------------------------------------------------------------
Tom "CaptZoom" Scarince
Mechanical Engineering Student at NJIT, Protector of Motherhood,
Defender of Fatherhood (in certain cases), and All Around Good Guy.
<<< SAVE THE BABY HUMANS >>>
-------------------------------------------------------------------------------
Lars-Henrik Eriksson
This brings up another question. While most ADF receivers I've seen have a
BFO setting, it's never used. What is its purpose? Are there SSB
transmitters out there that can be used? Where are they? Is there a list?
Are they of any use? Is this a fallback to an earlier era of equipment
that is no longere used/useful?
Sure it is used. There are NDBs where the ID signal is transmitted not
as a modulated audio signal, but as interrupts to the carrier (CW -
Continous Wave). During the period between ID's the beacon transmits a
continous carrier. When the ID is to be sent, the carrier is
interrupted shortly, then the ID is sent using the carrier only. After
another short pause, the carrier comes on again until the next ID
transmission.
Since there is no modulation, you cannot hear the ID signal in the
usual way. Instead the BFO (Beat Frequency Oscillator) setting is
used. It mixes the recieved signal with a signal of a slightly
different frequency. The mixing produces an audible signal, but only
when the carrier is present.
Tuning a CW beacon with the BFO turned on, you will heard a continous
beep which is interrupted by the ordinary ID signal.
CW beacons are rare in Europe, but you encounter one once in a
while. In some parts of the world CW (eg. former USSR, I think) CW
beacons are common.
On Jeppesen charts CW beacons have their IDs underlined.
--
Lars-Henrik Eriksson Internet: l...@sics.se
Swedish Institute of Computer Science Phone (intn'l): +46 8 752 15 09
Box 1263 Telefon (nat'l): 08 - 752 15 09
S-164 28 KISTA, SWEDEN Fax: +46 8 751 72 30
Julian Scarfe
Matthews) wrote:
> Somewhere in the world, more common a few decades ago...
>
> Some non-direction beacons identify with on-off keying of the carrier (A1
> modulation). The BFO provides a beat note making it easier to identify
> the station. Without the BFO, the sound heard from the ADF is a change in
> the background static, with a bit of popping at the switch transitions.
>
> The remaining question is, can anyone cite any operating examples of such
> beacons?
They're still common in Europe. The UK doesn't have any that I can think
of but they're common in France. As far as I remember MK (Calais OM) and
ONT (Kleine Brogel on B29 in Belgium) need that BFO. I believe the
original reason for choosing keyed-carrier was that it gives a better
range than modulation. This would be important when or where NDBs are the
standard method of navigation over large distances (a role now filled by
VORs).
Julian Scarfe
ja...@cus.cam.ac.uk
Earl=Morse%EM...@bangate.compaq.com
The main reason is that with AM a weak and a strong signal can be heard
simultaneously. The same scenario with FM would yield only the stronger
signal being received because of the capture effect that FM exhibits.
A pretty nasty scenario when strong signal station asks for a weather
report at the same time that the weak station announces he has lost
power and is going down.
Earl Morse
KZ8E
kz...@bangate.compaq.com
Gary Neff
: In article <phb.779996979@melpar>, p...@syseng1.melpar.esys.com (Paul H.
: Bock) wrote:
: Thanks.
: --
: Ace
You tune your ADF until the tone from the BFO disappears, then you're
right on freq.
--
Gary Neff <ga...@pacifier.com>
Ron Natalie
ground on 100.3 on the FM car radio. The difference is pretty close to
twice the radios IF frequency.
-Ron
David Stockton
: Then why did the land-mobile services (which started our using AM)
: switch to FM?
: Jeff NH6IL
Aircraft do tend to travel further afield. Changing over would
involve changing an airport and all the aircraft using it
simultaneously. These aircraft use other airports, so those must also
change at the same time - and so on. In this way the whole world (except
the odd reclusive country) would have to change over at once.
The capture effect is a discouragement, but on the other hand, much
aviation radio is of very poor audio quality and various incidents have
been attributed to this. There have been studies into changing to
improve speech clarity, but the inability to do a phased changeover has
always killed it.
Land mobile has been historically broken into small, isolated groups,
so a group could buy new FM gear when it wanted. Channel spacings
weren't affected. Joe's taxis could change quite independantly of the
fire brigade etc as the two systems are isolated.
Maritime VHF is FM because they used HF mainly, and only started
later on VHF, after FM was proven. Aircraft went for VHF early because
of the benefit of smaller antennae.
In the aviation world, dates have already been set for the shut-down
of ILS systems, a few years after the date set for the installation of
MLS. I wonder if some of the GPS based alternatives might throw a
spanner in the works ?
Cheers
David GM4ZNX
Bob Tortajada
commercial broadcast VHF in the 88 to 10? MHz range is FM). Explanations
please?
I do not know know for a fact why, but here a fact that I believe is
the reason.
FM takes up more bandwidth than AM. This means that there would be less
channels available for the same fequency range. The band could not support
360 or 720 channels if we used FM.
Hope this helps!!
--
--------------------------------------------------------
Bob Tortajada | Automated Securities
b...@brass.com | Weehawken, NJ
--------------------------------------------------------
Roy Smith
> In this way the whole world (except
> the odd reclusive country) would have to change over at once.
Why? You pick some unused band and simulcast AM on 118-136 MHz and FM on
the other one using channel-pairing. That way, planes equipped with the
new equpment can use it and people will the old stuff can continue to use
that. Gradually (after 10 or 20 years, or whatever interval seems
appropriate) you force the remaining few to switch over.
Not that I'm convinced this would be practical, but it's certainly
possible.
Jim Holtzman
I heard it was a matter of safety. If two fm radios key up at the same time,
the stronger one usually prevails. If a third party was listening, he would
not hear one of the other two transmitters. If AM is used, there will still
be some hetrodyning, but the message may still be heard.
What do you think of that, netters?
James Holtzman kc6ncg (holt...@shazam.ecs.csus.edu)
Roy Smith
> FM takes up more bandwidth than AM. This means that there would be less
> channels available for the same fequency range. The band could not support
> 360 or 720 channels if we used FM.
Well, FM usually takes more bandwidth than AM, but it doesn't have to. It's
been a long time since I studied this stuff, but there is a constant
(modulation index?) which is the ratio of the audio bandwidth to the
modulated bandwidth. The constant is usually greater than 1, but doesn't
have to be. In fact, I seem to remember reading that the original idea
behind FM was to *conserve* bandwidth by doing just that, and then somebody
discovered that you could improved S/N by using more bandwidth, and that
became the way everybody did it.
As a matter of fact, I just looked up the frequencies for my ICOM M-11
marine handheld. VHF-FM, on 25 khz channel spacing. For example:
Channel FX
20A 157.000
80A 157.025
21A 157.050
81A 157.075
22A 157.100
Marine band uses "channels" instead of frequencies in common lingo. Just
like the aviation band, it used to be 50 khz spacing and then they stuck
another set later in the gaps at 25 khz, which accounts for the crazy
channel numbering system.
Jerry Bransford
|> jer...@jerber.sandiego.sgi.com (Jerry Bransford) writes:
|>
|> >It's due to a simple fact that AM preceded FM and that AM is what was available when airplanes began using radios.
|> Then why did the land-mobile services (which started our using AM)
|> switch to FM?
|>
|> be detrimental, if not dangerous, to air-ground comms.
|>
|>
|> Jeff NH6IL
It still has little to do with FM capture effect. It's purely economic.
How old is the average airplane? How old is the average car that uses land-mobile radio service? And how much $$ does an aircraft radio cost compared to one suitable for a car? And typically it's the government user that uses land-mobile radio services who can decide to spend the $$$ because it's only tax dollars they are spending, not their own personal dollars.
Cars are replaced every few years, and end-users of land-mobile (typically government/taxi/police/fire) buying cars/trucks can make that switch to new radio technolgies with little or no economic impact. Not so with airplanes. Airplanes are NOT replaced regularily, and thus there is a huge economic cost for someone to mandate that airplanes *will* switch to the imcompatible FM mode.
And it would have had to have been mandated for *everyone* to switch to FM due to the incompatibilities between AM and FM
There are too many AM radios in airplanes, and when there was shortlived talk of FM for airplanes, it was thorougly trounced by a broad spectrum of airplane drivers/owners/operators for purely economic issues.
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry Bransford
Silicon Graphics
(619) 546-0409
PP-ASEL - KC6TAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Mike Connell
>Because the FM discriminator/detector of your FM radio is going to be able to hear (detect) some 'AM' information that was added as noise by the atmosphere to an FM signal during it's journey from the original (VOR) transmitter to your FM receiver, your FM radio will convert that 'AM' to an audio signal you can hear.
>The AM component of FM is usually just noise, but your FM receiver (not being 100% perfect) will usually also allow you to hear some of the VOR's morse code I.D. dits and dahs, even though they were actually sent in an AM format. A 'really' good FM receiver will have 'limiters' that eliminate the AM component of an FM signal so you either barely or can't at all hear the dits and dahs of the VOR's signal.
>Quite often, an FM receiver is designed poorly enough so you can understand AM type transmissions fairly well. A really good FM receiver will almost eliminate your ability to understand an AM signal, becuase 'AM' to an 'FM' signal is really a noise component. AM is an undersirable component that is tried to be eliminated entirely by design in any FM receiver.
>No matter what the mode, AM, FM, SSB, CW, or whatever, if your radio can tune in that frequency, you'll usually hear 'something', even if your receiver isn't designed to receive that particular mode. For example, a shortwave receiver that isn't designed for SSB (single side-band) will still hear 'something', but it's gibberish.
>And by the way, for those that asked about the BFO knob on some receivers and direction finders, some navigational aids (transmitters) from 'years back' contained a signal (carrier frequency), but no modulation (no AM, FM or CW component on top of the 'carrier' frequency). You couldn't hear the signal properly without the BFO turned on and adjusted to produce an audible signal.
>The BFO (beat frequency oscillator) adds a new frequency/signal to the carrier frequency which are then mixed together to produce a third (the difference between the original two frequencies) signal, which is then an audible signal you can hear.
>Bottom line, the BFO makes an inaudible or barely audible signal audible. Without a BFO, you might hear hissing like 'ss-ssssss-ss-ss-ssssss-. After the BFO is turned on, you then hear 'dit-dah-dit-dit-dah'.
>Regards,
>--
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>Jerry Bransford
>Silicon Graphics
>(619) 546-0409
>PP-ASEL - KC6TAY
I will add my 2 cents worth.
Could it be that when 2 or more aircraft double (both aircraft talk
at the same time) the controller will hear the beat note and know that a
nother aircraft was talking. This would not happen with a FM
Jeffrey Herman
> Aircraft do tend to travel further afield. Changing over would
>involve changing an airport and all the aircraft using it
>simultaneously. These aircraft use other airports, so those must also
>change at the same time - and so on. In this way the whole world (except
>the odd reclusive country) would have to change over at once.
Nice argument but it has flaws.
Recall back in the mid-70's the transition the MF marine band went
through: AM to SSB. We at the Coast Guard Radio Stations, during
that transition period, made our MF voice broadcasts in such a way
that those with either AM or SSB radios could copy us. The ITU set a
specific date in which AM would no longer be allowed; it was up to
boat/ship owners to equip their vessels with SSB by that date. This
was a worldwide transition.
Keep in mind there were more ships/boats involved in that change-of-
mode transition than there would be airplanes today. [And boy what
fun it was picking up those marine radios practically for free
and using them on 80 and 160M!]
If aviation were to switch from AM to FM (or even SSB) the control
towers, just like the Coast Guard, would have to maintain equipment
on both modes during the transition period; it wouldn't have to
be a change done simultaneously worldwide as implied in your
article.
I would think that SSB would be the perfect mode for VHF aviation comms
since there's no capture effect when two stations xmt at the same time;
HF aviation comms have of course been using SSB for decades.
> Land mobile has been historically broken into small, isolated groups,
>so a group could buy new FM gear when it wanted. Channel spacings
>weren't affected. Joe's taxis could change quite independantly of the
>fire brigade etc as the two systems are isolated.
Again, the switch from AM to SSB on the MF marine band was worldwide.
> Maritime VHF is FM because they used HF mainly,
you mean MF of course; prior to the incorporation of the VHF marine
band mariners used the 2-3 Mc band for coastal comms.
>and only started
>later on VHF, after FM was proven.
Not quite. Maritime VHF FM came into use in the mid-70's at the same time
the world went through the AM to SSB transition. FM in general was a proven
mode in the 50's.
>Aircraft went for VHF early because
>of the benefit of smaller antennae.
Hmmmm... More important is the limited line-of-sight capability
of VHF for local comms; an aircraft wishing to contact a tower only
100 miles away might have difficulty on an HF aircraft band.
Jeff NH6IL
Martin Heffels
jef...@kahuna.tmc.edu (Jeffrey Herman) writes:
> jer...@jerber.sandiego.sgi.com (Jerry Bransford) writes:
>
> >It's due to a simple fact that AM preceded FM and that AM is what was available when airplanes began using radios.
>
> Then why did the land-mobile services (which started our using AM)
> switch to FM?
>
> I think the best answer so far was that FM's capture effect would
> be detrimental, if not dangerous, to air-ground comms.
AM also suffers much from ignition noise, generated by cars, which makes
mobile comms very difficult.
73, PE1EEC
-martin-
----------------------------------------------------------------------------
e-mail: z...@cpzap.xs4all.nl
'This message was brought to you, with the help of subluminal advertising.'
Mark A. Matthews
>AM also suffers much from ignition noise, generated by cars, which makes
>mobile comms very difficult.
In article <35uf24$m...@cmcl2.nyu.edu>,
Roy Smith <r...@mchip00.med.nyu.edu> wrote:
>Why should a gasoline piston engine in a car produce any more or less
>ignition noise than a gasoline piston engine in an airplane? In fact, the
>airplane has twice as much ignition stuff per cylinder, so I would expect it
>to produce more.
Shielding. In a typically automobile, ignition noise suppression efforts
are pretty much limited to resistive plugs and plug wires, to take some of
the sharp edges off the ignition pulse. Most all other filtering efforts
are within the receiver portion of the car radio, and besides, we all know
AM is dead these days...
Aircraft ignition systems feature full shielding from magneto to plug
electrode, with flexible metal braid covering the harness and fully shielded
plugs. Receivers have noise suppression circuits on the power leads, and
(relatively) complex noise blanking circuits. But ignition noise is still
often a problem.
(Prediction - when Slick's new electronic ignition system comes into
wide-spread use, we'll see a rise in ignition noise complaints. Electronic
ignition have a higher voltage spark with a faster rise-time, thus providing
a lot more energy to radiate. Then we'll all have to get new resistive
ignition harnesses and plugs. Slick's pretty smart, eh?)
The reason we still have AM comms is purely economic - You'll never get a
change through which will replace the AM system without a major squeal from
aircraft owner groups. "Too expensive", they'll say. "Unfair to the little
guy", will be the cry. Heck, we can't even legislate out the old 90 channel
radios.
-Mark
kevin jessup
>There are too many AM radios in airplanes, and when there was shortlived talk of FM for airplanes, it was thorougly trounced by a broad spectrum of airplane drivers/owners/operators for purely economic issues.
What would an (FAA accepted?) FM radio cost? What is the total
anual cost (hangar/ground space, inspections, maintenance, fuel) of
operating a single engine plane? Is a radio upgrade going to break the
bank? What is the cost of a new radio as a percentage of yearly (or
even amortize it over 5 years) operating expenses? I'm not saying your
wrong, just curious about yearly operating costs.
I'd suspect the hobby of aviation has just as many people reluctant
to "upgrade" as does the hobby of amateur radio. I still hear local
repeater chatter regarding the "problem" of "upgrading" your HT
to PL when one's favorite repeater moves from "carrier only access"
to full-time "PL tone" access. As if PL is some high-tech luxury!
Bruce G. Bostwick
Roy Smith <r...@mchip00.med.nyu.edu> wrote:
>Why should a gasoline piston engine in a car produce any more or less
>ignition noise than a gasoline piston engine in an airplane? In fact, the
>airplane has twice as much ignition stuff per cylinder, so I would expect it
>to produce more.
Aircraft ignition systems are much more carefully shielded than those
in your car. A lot of them have the plug wires encased in an ignition
wire shield that is essentially conductive conduit (shielded plugs
have threaded fittings on _both_ ends to connect to this conduit)
which may be flexible copper braid or actual rigid tubing (usually in
radials or older inline or vee engines). This essentially
completely kills the plug noise in the radios. The unshielded systems
are usually very carefully balanced with caps and chokes to minimize
the radiated RF.
Aircraft radios, BTW, are sensitive to signals in the nV/M range -- if
somebody starts their car on the ramp, you can definitely hear it even
50' away with your squelch turned down ... strobes make a fun noise
too ...
--
<BGB>
li...@ccwf.cc.utexas.edu / The purpose of technology is not
(really Bruce Bostwick) / to confuse the mind, but to serve
from the great state of TEXAS / the body. -- W.S. Burroughs
Curtis Wheeler
>dst...@hpqmdla.sqf.hp.com (David Stockton) wrote:
>> In this way the whole world (except
>> the odd reclusive country) would have to change over at once.
>Why? You pick some unused band and simulcast AM on 118-136 MHz and FM on
>the other one using channel-pairing. That way, planes equipped with the
>new equpment can use it and people will the old stuff can continue to use
>that. Gradually (after 10 or 20 years, or whatever interval seems
>appropriate) you force the remaining few to switch over.
>Not that I'm convinced this would be practical, but it's certainly
>possible.
From a technical standpoint it would be possible. However there isn't any
suitable RF spectrum available for such an undertaking.
Curtis Wheeler San Ramon, CA (cg...@chevron.com)
KD6ELA / GROL PG10-25691 / Pvt. Pilot ASEL
Jer/ Eberhard
> What would an (FAA accepted?) FM radio cost? What is the total
> annual cost (hangar/ground space, inspections, maintenance, fuel) of
> operating a single engine plane? Is a radio upgrade going to break the
> bank? What is the cost of a new radio as a percentage of yearly (or
> even amortize it over 5 years) operating expenses? I'm not saying your
> wrong, just curious about yearly operating costs.
They must be FCC type accepted for the FAA to approve them.
Yes, a new radio stack can cost from $9,000 to $28,000 and up...
This for an airplane that you bought 10 years ago for $18,000.
Yes, this would "break the bank".
> I'd suspect the hobby of aviation has just as many people reluctant
> to "upgrade" as does the hobby of amateur radio. I still hear local
> repeater chatter regarding the "problem" of "upgrading" your HT
> to PL when one's favorite repeater moves from "carrier only access"
> to full-time "PL tone" access. As if PL is some high-tech luxury!
If you think aviation is a hobby like ham radio, you have another (free)
think coming. Many of us airplane owners and former airplane owners put
almost every available dollar into our love of flying (for fun or for
work). Ask anyone who owns (or shares) an airplane about what else they
have or do. Usually, we can make do with a 10 year old car, live in an
apartment, or a house we bought more than 10 years ago, no "cruise"
vacations, no " 2 week ski" vacations, no cabin in the woods, no boat or
camper... yes, almost every available dollar not required directly for
subsistence goes into aviation. It is our choice.
What we object to is the "do gooders, with a better idea" who tell us...
"this is how you should spend your money... and we'll pass a law making
you buy new (transponders, radios, et.al.), just to make sure you do"!
Yes, PL is some high-tech luxury. The luxury is polluting the airways
with all the garbage instead of filtering it out AT THE SOURCE! Putting
PL on a repeater masks the problem, while creating another one, without
fixing the first one! Bad engineering! Bad idea!
Jer/ "Yes, I'm a pilot, a CFI and a ham" Eberhard
--
Jer/ (Slash) Eberhard, j...@fc.hp.com, OFFICE 303 229-2861, FAX 303 229-3598
Hewlett-Packard SST, 3404 East Harmony Road MS-74, Ft Collins, CO 80525-9599
N0FZD, Civil Air Patrol, PikesPeak 218, MSN CheckPilot, CFII Airplane & Glider
FAA Aviation Safety Counselor, Denver FSDO, 18 Young Eagles Flown!
Bruce Bateman
>...<snip>...
>
> In the aviation world, dates have already been set for the shut-down
>of ILS systems, a few years after the date set for the installation of
>MLS. I wonder if some of the GPS based alternatives might throw a
>spanner in the works ?
>
> Cheers
> David GM4ZNX
As of about 2 months ago, the FAA has cancelled the MLS program in
favor of GPS. I believe that they will only continue pursuing MLS
installations at those locations where necessary to meet
international agreements (I assume this means at the big
internation airports that see significant volume of non-US
aircarriers).
Bruce Bateman
Roy Smith
>AM also suffers much from ignition noise, generated by cars, which makes
>mobile comms very difficult.
Why should a gasoline piston engine in a car produce any more or less
ignition noise than a gasoline piston engine in an airplane? In fact, the
airplane has twice as much ignition stuff per cylinder, so I would expect it
to produce more.
x3670
> I think the best answer so far was that FM's capture effect would
> be detrimental, if not dangerous, to air-ground comms.
I read somewhere recently that it was due to the cost of having to
switch over to all new equipment, and the FAA or whoever finally
just said "The heck with it."
Ed Lieser
Allen-Bradley Co.
Gary Coffman
>I would think that SSB would be the perfect mode for VHF aviation comms
>since there's no capture effect when two stations xmt at the same time;
>HF aviation comms have of course been using SSB for decades.
No, for two reasons. First, air traffic centers have DF equipment that
depend on a steady carrier to work. This is used very often to find
"lost" general aviation aircraft. And second, keeping all those radios
on channel closely enough to be intelligble on SSB would be a major
chore. That's why ACSSB was invented, to allow a pilot carrier for AFC
(and compandoring). If a change were to be made, ACSSB would be the
logical choice.
Gary
--
Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems | we break it. | uunet!rsiatl!ke4zv!gary
534 Shannon Way | Guaranteed! | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244 | | ga...@ke4zv.atl.ga.us
Charlie Gibbs
>Nice argument but it has flaws.
>
>Recall back in the mid-70's the transition the MF marine band went
>through: AM to SSB. We at the Coast Guard Radio Stations, during
>that transition period, made our MF voice broadcasts in such a way
>that those with either AM or SSB radios could copy us. The ITU set a
>specific date in which AM would no longer be allowed; it was up to
>boat/ship owners to equip their vessels with SSB by that date. This
>was a worldwide transition.
>
>Keep in mind there were more ships/boats involved in that change-of-
>mode transition than there would be airplanes today. [And boy what
>fun it was picking up those marine radios practically for free
>and using them on 80 and 160M!]
On the other hand, marine radios are _MUCH_ cheaper than aircraft
radios. I recently installed a King KX97A (comm only) to replace
a navcom that literally went up in smoke. After the dust settled,
it cost me just over $2000 (although that's our Canuck mini-bucks
and installation was included). I don't know exactly how much a
marine radio costs, but I suspect it's no more than a fifth of
that amount - not nearly as hard to take.
Charli...@mindlink.bc.ca
If your nose runs and your feet smell, you're built umop-apisdn.
Curtis Wheeler
>I will add my 2 cents worth.
>Could it be that when 2 or more aircraft double (both aircraft talk
>at the same time) the controller will hear the beat note and know that a
>nother aircraft was talking. This would not happen with a FM
In the the world of AM, the "beat note" would not be heard if both
transmitters are on the exact same frequency (with no modulation).
Hetrodyning occurs in FM also when two stations are received with close to the
same signal strength (and "close" is relative term). That beat will usually
be a lower frequency that changes in relation to the two modulating signals -
sounding like an electric razor when you are running it over your face.
There is not that much difference in the capture effect of AM or FM. A strong
AM signal will completly step on a weaker AM signal with no problem. IMHO the
so called capture effect of FM would not be an issue if we were really faced
with changing from AM to FM.
Why is AV-COM an AM system? I don't know. I imagine it was the more proven
technology when the spectrum was allocated and the international standards
(and treaties) were set. Making a change now would take as much, or greater
political effort as technological effort. The technical change would be a no
brainer - it's keeping the WORLD of aviation compatable that would be tough.
Jeffrey Herman
>It still has little to do with FM capture effect. It's purely economic.
>How old is the average airplane? How old is the average car that uses land-mobile radio service? And how much $$ does an aircraft radio cost compared to one suitable for a car? And typically it's the government user that uses land-mobile radio services who can decide to spend the $$$ because it's only tax dollars they are spending, not their own personal dollars.
************************************************************************
How old is the average ship? See my article concerning the mid-70's
worldwide transition from AM to SSB on the maritime MF band.
And note that shipboard radio equipment prices rival that of aircraft.
**********************************************************************
Jerry continues:
>Cars are replaced every few years, and end-users of land-mobile (typically government/taxi/police/fire) buying cars/trucks can make that switch to new radio technolgies with little or no economic impact. Not so with airplanes. Airplanes are NOT replaced regularily, and thus there is a huge economic cost for someone to mandate that airplanes *will* switch to the imcompatible FM mode.
***********************************************************************
Ships don't get replaced all the often yet the owners endured the
change of mode.
{Jerry, it's quite difficult editing your articles if you don't use
the return key at the end of each line.}
Jeff NH6IL
Robert V. Grizzard
: z...@cpzap.xs4all.nl (Martin Heffels) writes:
: >AM also suffers much from ignition noise, generated by cars, which makes
: >mobile comms very difficult.
: Why should a gasoline piston engine in a car produce any more or less
: ignition noise than a gasoline piston engine in an airplane? In fact, the
: airplane has twice as much ignition stuff per cylinder, so I would expect it
: to produce more.
The airplane has shield braid running from the magneto to the plug, and
the spark plug is designed to ground the braid. Dunno about the magneto end.
Yes, "Magneto". It's possible too that the magneto has a slower rise
time that indicates that fewer of those nasty interference-making
high-frequency harmonics are being generated. I don't know; I've never
found anything that looks at this angle.
de kg7yy (from rec.radio.amateur.misc)
Alan Larson
>Recall back in the mid-70's the transition the MF marine band went
>through: AM to SSB. We at the Coast Guard Radio Stations, during
>that transition period, made our MF voice broadcasts in such a way
>that those with either AM or SSB radios could copy us. The ITU set a
>specific date in which AM would no longer be allowed; it was up to
>boat/ship owners to equip their vessels with SSB by that date. This
>was a worldwide transition.
>
>Keep in mind there were more ships/boats involved in that change-of-
>mode transition than there would be airplanes today.
I would kind of guess against this. There are probably in the vicinity
of 250,000 aircraft in the U.S. alone. I would not be suprised if there
were, in fact, twice that many.
>I would think that SSB would be the perfect mode for VHF aviation comms
>since there's no capture effect when two stations xmt at the same time;
>HF aviation comms have of course been using SSB for decades.
I disagree. As an active pilot, I would *MUCH* prefer FM to SSB. I
want a mode where there will be no modulation of the received signal by
signal strength flutter if (for example) the reception path happens to
be through my propeller. I want the maximum signal clarity. I want a
mode where signals are of consistant volume level from the receiver.
SSB fails in all of these counts.
>Again, the switch from AM to SSB on the MF marine band was worldwide.
How many stations switched? A lot, I bet. Still, there are lots of
airports -- many of them are inland.
Given all this, I would really love to have aviation radio be FM with
20 kHz spacing. That works just fine for my 2 meter rig with essentially
no interference from the next channel over -- aircraft radios generally
are such junk that they hear stations 25 or 50 kHz away. More channels,
real audio fidelity, levels consistent in the noisy aircraft -- lots of
advantages.
About the only time the capture effect would be likely to matter is when
one of the aircraft is vastly closer to the receiver. It could well be
an advantage on 122.8 for traffic announcements. You would hear the local
ones, and not lose them to the ones from 50 and 100 miles away.
Alan
wayne roberts
: Someone subsequently asked me *why* they are AM not FM (after all,
: commercial broadcast VHF in the 88 to 10? MHz range is FM). Explanations
: please?
when two planes talk at the same time there usually is a tone which can
be heard because of the difference of carrier frequency. This is called
heterodyne. On FM, its considerably less pronounced.
Another interesting note is that the military aircraft range 225-400mhz
is primarily AM. So is the new air-phone in the 848-851/894-896 range.
Michael J Dower
griz...@indirect.com "Robert V. Grizzard" writes:
> Roy Smith (r...@mchip00.med.nyu.edu) wrote:
> : z...@cpzap.xs4all.nl (Martin Heffels) writes:
> : >AM also suffers much from ignition noise, generated by cars, which makes
> : >mobile comms very difficult.
>
> : Why should a gasoline piston engine in a car produce any more or less
> : ignition noise than a gasoline piston engine in an airplane? In fact, the
> : airplane has twice as much ignition stuff per cylinder, so I would expect it
> : to produce more.
>
> The airplane has shield braid running from the magneto to the plug, and
> the spark plug is designed to ground the braid. Dunno about the magneto end.
The magnetos I used to work on had metal casings - this would help shield
interfering EM radiation.
AFAIK, there are two types of aircraft ignition systems using magnetos -
high tension and low tension. The former generates a high voltage at the
magneto, while the latter generates a low voltage at the magneto and uses
transformers at *every* plug to convert this to high voltage. I've not seen
many of the latter type!
Grounding in aircraft is way ahead of that used in ground vehicles. All
metallic surfaces are electrically bonded together - usually by short wires.
Even the moving control surfaces, oleo legs, etc., are treated this way.
The reason is primarily because of static discharge and lightning protection,
but it sure helps for the radio side of things, too.
In Australia, aircraft COMMS made the switch to ssb over a couple of years
during the early '80s. (HF, anyway - I cannot remeber about the vhf part).
I remember being an apprentice working on the "ssb mod." on one of our
F-27's. Unfortunately, it was very early on, and I was just learning about
radio, and my job was terminating a lot of control/power wires - that's why
I'm not fully versed in all that happened during the mod.!
We had one old F-27 that was moth-balled, and this somehow "slipped
thru the cracks" for the mod's. We lined up a buyer for it, and finally it
looked like we'd get it off our hands ... then one of our guys realised
that it couldn't fly because it didn't have ssb!
> Yes, "Magneto". It's possible too that the magneto has a slower rise
> time that indicates that fewer of those nasty interference-making
> high-frequency harmonics are being generated. I don't know; I've never
> found anything that looks at this angle.
Could be something here - it works on a *slightly* different principle than
motor vehicle ignition.
--
Mike Dower
G0VEY 'Quoth the raven, "Never more".' ... Poe
VK2ENG
Bob Furtaw
Matthews) wrote:
> In article <ajmilan-19...@130.151.88.243>,
> Andrew J. Milan <ajm...@msmacab.remnet.ab.com> wrote:
> >This brings up another question. While most ADF receivers I've seen have a
> >BFO setting, it's never used. What is its purpose? Are there SSB
> >transmitters out there that can be used? Where are they? Is there a list?
> > Are they of any use? Is this a fallback to an earlier era of equipment
> >that is no longere used/useful?
>
> Somewhere in the world, more common a few decades ago...
>
> Some non-direction beacons identify with on-off keying of the carrier (A1
> modulation). The BFO provides a beat note making it easier to identify
> the station. Without the BFO, the sound heard from the ADF is a change in
> the background static, with a bit of popping at the switch transitions.
>
> The remaining question is, can anyone cite any operating examples of such
> beacons?
>
> -Mark
A long, long time ago, there was aviation weather transmitted, using CW in
the LF band. The BFO (Beat Frequency Oscillator) was required in order to
hear the morse code properly since the signal was CW (actually ICW
(interupted)) and not MCW (modulated) that is now used for ID today. The
last station to transmit this in the US was from Key West, I believe (this
might be wrong) but there are no more in the U.S. Therefore, the BFO is
now a vestige and today has no practical purpose.
Bob Furtaw - W8IL fur...@comm.mot.com
CFI-A/G/I/MEI, CGI-A/I
All disclaimers ever written by anybody apply. :-)
Serge Burjak
: Jeffrey Herman (jef...@kahuna.tmc.edu) wrote:
: : Then why did the land-mobile services (which started our using AM)
: : switch to FM?
: : Jeff NH6IL
: Aircraft do tend to travel further afield. Changing over would
: involve changing an airport and all the aircraft using it
...stuff deleted
: In the aviation world, dates have already been set for the shut-down
: of ILS systems, a few years after the date set for the installation of
: MLS. I wonder if some of the GPS based alternatives might throw a
: spanner in the works ?
MLS has now been discredited and will not be used. GPS approaches are
being drawn up all over the world.
Cheers,
Serge
VK4BSB
Jeffrey Herman
REC.RADIO - IF YOUR COMMENTS ARE NOT RADIO RELATED
THEN PLEASE DELETE THE REC.RADIO GROUP.
Sorry for shouting...
Jeff NH6IL
Bob Furtaw
wrote:
> Andrew J. Milan (ajm...@msmacab.remnet.ab.com) wrote:
> : In article <phb.779996979@melpar>, p...@syseng1.melpar.esys.com (Paul H.
> : Bock) wrote:
>
>
> : SSB
> : > requires that a beat frequency oscillator be "on" in the receiver,
> : > which causes AM to sound like one big squeal. Conversely, SSB
> : > sounds like a bunch of ducks quacking on a an AM receiver (no BFO).
> : >
> : > Similarly, AM and FM are also totally incompatible when used
> : > on the same frequency (disregarding "slope detection" of FM on an AM
> : > receiver, which doesn't really count).
> : >
>
> : This brings up another question. While most ADF receivers I've seen have a
> : BFO setting, it's never used. What is its purpose? Are there SSB
> : transmitters out there that can be used? Where are they? Is there a list?
> : Are they of any use? Is this a fallback to an earlier era of equipment
> : that is no longere used/useful?
>
> : Thanks.
> : --
> : Ace
>
> You tune your ADF until the tone from the BFO disappears, then you're
> right on freq.
Negative! The BFO is adjusted (at the factory) so that it is slightly off
frequency so you can hear the beat (hence the name). When you zero beat
this by tuning the dial, you will be slightly off center of the passband of
the signal being received, and therefore lose maximum sensitivity and allow
for picking up unwanted signals. If you use a digital receiver, you don't
run into this tuning problem. If you use an old continuously tunable type,
set the ADF in receive mode, find the station by first "roughing in" the
frequency, listen for the coded ID, then center the freuency by listening
the the "reduction of high frequencies in the audio" (this is a swishing
sound that gets lower in pitch as you center the frequency, take a little
practice). Then place the ADF in "ADF" mode.
> --
> Gary Neff <ga...@pacifier.com>
Alan Larson
>(Jerry Bransford) writes:
->
->>It still has little to do with FM capture effect. It's purely economic.
->>How old is the average airplane? How old is the average car that uses land-mobile radio service? And how much $$ does an aircraft radio cost compared to one suitable for a car? And typically it's the government user that uses land-mobile radio services who can decide to spend the $$$ because it's only tax dollars they are spending, not their own personal dollars.
->************************************************************************
->
->How old is the average ship? See my article concerning the mid-70's
->worldwide transition from AM to SSB on the maritime MF band.
->
->And note that shipboard radio equipment prices rival that of aircraft.
->
->
->**********************************************************************
->Jerry continues:
->
->>Cars are replaced every few years, and end-users of land-mobile (typically government/taxi/police/fire) buying cars/trucks can make that switch to new radio technolgies with little or no economic impact. Not so with airplanes. Airplanes are NOT replaced regularily, and thus there is a huge economic cost for someone to mandate that airplanes *will* switch to the imcompatible FM mode.
->***********************************************************************
->
->Ships don't get replaced all the often yet the owners endured the
->change of mode.
->
->{Jerry, it's quite difficult editing your articles if you don't use
->the return key at the end of each line.}
How many airplanes are there in the world that would be affected?
How many ships were affected? I think you will find that there are
lots more aircraft, and lots more airports.
Jeff, it is quite difficult replying by mail to your articles because
your news software is giving an invalid address on the From: header.
Please contact your system administrator -- you are *NOT* at tmc.edu,
according to the administrator of tmc.edu. Is it asking too much that
you follow the standards... ("good usenet operating practices...")
Alan
David Stockton
: From a technical standpoint it would be possible. However there isn't any
: suitable RF spectrum available for such an undertaking.
: Curtis Wheeler San Ramon, CA (cg...@chevron.com)
It's not just the spectrum, there's the space needed for duplicate
antennae, radios and controls. You certainly wouldn't want to do this on
an aircraft, but even on the ground (the place where duplication would
be essential) the nuisance factor just builds up. Duplicate VOLMET,
duplicate VOR networks...
As you said, technically possible, but administratively very
challenging !
I'm assuming that aircraft would not need to go dual mode, that any
spectrum would be too far away for antenna sharing, and that anyway, a
clean separation would be needed to allow the old gear to be junked at
the end of the overlap period, without forcing any refitting of the
new stuff.
Cheers
David GM4ZNX
Tim Kramer
>
> What we object to is the "do gooders, with a better idea" who tell us...
> "this is how you should spend your money... and we'll pass a law making
> you buy new (transponders, radios, et.al.), just to make sure you do"!
>
>
I may have problems with in my flying the Comm radios are not among them.
My goal is better, cheaper and safer flying not more radios. At last
count I had seven radios and I realy don't feel that I need any more and I
certainly don't feel the need to change the ones I have.
Tim Kramer
N30450 C-177A
Craig Deibele
>In article <1994Sep20....@njitgw.njit.edu> ths...@hertz.njit.edu (,, Tom 'CaptZoom' Scarince) writes:
>>Um, I'm just a dumb piston head, not a pointy headed radio guy, but if VHF
>>aircraft communications are AM, then why can I hear the local VOR by tuning my
>>cheap FM radio to the top of the scale?
>
>VOR signals are considered NAV signals, not COM. Nav/com radios have a
>separate receiver for each. There is an FM component to VOR signals.
>
it could also be that the AM transmitted on the VOR does not have much
bandwidth. You can demodulate a narrowband signal that is modulated
by either FM or AM with either FM or AM. A little distortion, but
i've done this many times.
craig
Jeffrey Herman
> Jeff, it is quite difficult replying by mail to your articles because
>your news software is giving an invalid address on the From: header.
>Please contact your system administrator -- you are *NOT* at tmc.edu,
>according to the administrator of tmc.edu. Is it asking too much that
>you follow the standards... ("good usenet operating practices...")
Wow, Alan - no need to be so mean. The folks here know about the
invalid default address and are working on it. I've posted my
real address to the net several times in the past.
This is a university with 48,000 students - the computer center
has it's hands full with other problems besides the invalid
address. They set the standards, not me!
73 from Hawaii,
Jeff NH6IL
jef...@math.hawaii.edu (pay attention, Alan!)
Roy Smith
> I don't know exactly how much a marine radio costs, but I suspect it's no
> more than a fifth of that amount - not nearly as hard to take.
A high-quality marine VHF handheld (5 or 6W transmit power, every possible
channel, scanner, programable memory, waterproof-ish, etc) from a reputable
manufacturor (ICOM or Standard) should be under $400. A perfectly usable
console-mount one (25W transmit and similar quality from a good
manufacturer but with fewer bells and whistles which you don't really need
anyway) can be had for under $200.
There really isn't that much difference between a marine and a aviation
radio (except, of course, that the aviation set has a NAV rcvr built in,
but my guess is that the extra panel display and controls cost more to add
than the extra electronics). But, the marine sets don't have to worry
about such a strict certification process, don't have the liability
headache, and are probably made in production quantities 10-100 times as
large as their aviation brethren.
On the other hand, marine sets *do* have to be some approximation to
waterproof, which probably adds quite a bit to the cost.
C. C. (Clay) Wynn, N4AOX
>In article <CwLwz...@news.Hawaii.Edu> jef...@math.hawaii.edu writes:
>>(Jerry Bransford) writes:
>->
>->>It still has little to do with FM capture effect. It's purely economic.
I just got back from a lecture on the communication system for the early NASA
space activities at our radio club. The capcom radios used in the Mercury
program, (1962) and I think he said the Gemini program were all AM on HF, VHF.
The lecturer said there were problems with the doppler effect and with antenna
polarization, even on AM. Could these be more of a problem on FM, and be
another reason why AM was used there and is still used on aircraft?
What about weight? Weight is not a problem with land mobile but every ounce
counts on spacecraft/aircraft. Does a comparable NBMF radio weigh more than
an AM radio? One of the first FM applications were radios on WWII battle
tanks.
Sorry if I am late posting to this thread, it just became interesting after the
NASA radio lecture.
73,
C. C. (Clay) Wynn, N4AOX
w...@ornl.gov
=========================================================================
= Cooperation requires participation. Competition teaches cooperation. =
=========================================================================
Martin Heffels
r...@mchip00.med.nyu.edu (Roy Smith) writes:
> z...@cpzap.xs4all.nl (Martin Heffels) writes:
> >AM also suffers much from ignition noise, generated by cars, which makes
> >mobile comms very difficult.
>
> Why should a gasoline piston engine in a car produce any more or less
> ignition noise than a gasoline piston engine in an airplane? In fact, the
> airplane has twice as much ignition stuff per cylinder, so I would expect it
> to produce more.
Because an a/c engine is much better shielded than a car's engine.
-martin-
----------------------------------------------------------------------------
e-mail: z...@cpzap.xs4all.nl
'This message was brought to you, with the help of subluminal advertising.'
Martin Heffels
cg...@chevron.com (Curtis Wheeler) writes:
> In article <roy-2209...@mchip8.med.nyu.edu> r...@nyu.edu (Roy Smith) writes:
>
> >dst...@hpqmdla.sqf.hp.com (David Stockton) wrote:
> >> In this way the whole world (except
> >> the odd reclusive country) would have to change over at once.
>
> >Why? You pick some unused band and simulcast AM on 118-136 MHz and FM on
> >the other one using channel-pairing. That way, planes equipped with the
> >new equpment can use it and people will the old stuff can continue to use
> >that. Gradually (after 10 or 20 years, or whatever interval seems
> >appropriate) you force the remaining few to switch over.
>
> >Not that I'm convinced this would be practical, but it's certainly
> >possible.
>
> From a technical standpoint it would be possible. However there isn't any
> suitable RF spectrum available for such an undertaking.
Well it depends. Here at the AT-Centre we use paired VHF-UHF frequencies,
which multicast upon demand. This is done for civil/military coordination.
It will however be from a human standpoint impossible. If it's busy, then it
takes a lot from the controller to listen to both frequencies together.
But then, the militaries don't use these frequencies, because they have their
own ATC's.
Bruce Bateman
>Charli...@mindlink.bc.ca (Charlie Gibbs) wrote:
>> I don't know exactly how much a marine radio costs, but I suspect it's no
>> more than a fifth of that amount - not nearly as hard to take.
>
>A high-quality marine VHF handheld (5 or 6W transmit power, every possible
>channel, scanner, programable memory, waterproof-ish, etc) from a reputable
>manufacturor (ICOM or Standard) should be under $400. A perfectly usable
>console-mount one (25W transmit and similar quality from a good
>manufacturer but with fewer bells and whistles which you don't really need
>anyway) can be had for under $200.
>
>There really isn't that much difference between a marine and a aviation
>radio (except, of course, that the aviation set has a NAV rcvr built in,
>but my guess is that the extra panel display and controls cost more to add
>than the extra electronics). But, the marine sets don't have to worry
>about such a strict certification process, don't have the liability
>headache, and are probably made in production quantities 10-100 times as
>large as their aviation brethren.
>
Given all the above, as I've scanned the ad's, etc, I've yet to see a
panel mount COM-only radio for less than $1000. As I recall, the
NARCOs and TERRAs seem to run in the $1200-$1500 range. The "cheap"
KINGs still seemed to push $2000. (Pardon if I'm off, I'm going on
memory here.) The point being that Mr. Gibbs' estimate of a 5x
differential in price betweem Av radios and marine radios is
reasonably good to optimistic. And in a large number of airplanes
( >50%? ) you have two COM radios to replace, not just one! AND,
in a large number of airplanes ( >50%? ), the COM radio IS integrated
with a NAV radio, which roughly doubles the cost again! And there
is the added expense of having a certified radio shop do the
installation and sign off the work (crude guess: 4-8hrs at $50-$100
per hour - lets call it $400). So a typical owner is looking at
somewhere between $2K - $10K to change over from AM to FM VHF.
And what does he get for this draining of his pocket book?
Clearer reception? Greater range? Fewer stepped on xmitions?
Based on the contradictory "facts" I watched go back and forth
regarding this topic, I'd have to conclude that its little or
none of the above. What he would get is brand new radios
at the expense of better maintenance, or a storm-scope, or
a GEM EGT gauge, or an IFR GPS, or .... - all of which would
probably have a much greater impact on the safety of flight
than would an FM VHF COM radio. So before we run off and decide
to make this change over to "modern" technology, lets see if the
benefits out weight the costs.
Bruce Bateman
Roger Grady
In article <35uf24$m...@cmcl2.NYU.EDU>, r...@mchip00.med.nyu.edu (Roy Smith) writes:
> z...@cpzap.xs4all.nl (Martin Heffels) writes:
> >AM also suffers much from ignition noise, generated by cars, which makes
> >mobile comms very difficult.
>
> Why should a gasoline piston engine in a car produce any more or less
> ignition noise than a gasoline piston engine in an airplane? In fact, the
> airplane has twice as much ignition stuff per cylinder, so I would expect it
> to produce more.
Which is why aircraft have a completely shielded ignition system -
wires, plugs, mags, everything.
Roger Grady K9OPO c21...@kocrsv01.delcoelect.com
Delco Electronics Corp. Kokomo, IN
"All information and opinions are personal unless otherwise stated."
Alan Larson
>I just got back from a lecture on the communication system for the early NASA
>space activities at our radio club. The capcom radios used in the Mercury
>program, (1962) and I think he said the Gemini program were all AM on HF, VHF.
>The lecturer said there were problems with the doppler effect and with antenna
>polarization, even on AM. Could these be more of a problem on FM, and be
>another reason why AM was used there and is still used on aircraft?
The doppler effect for a low orbit spacecraft will provide about 3 kHz of
shift from the center frequency at 146 MHz. Since copy is quite adequate
with my 2 meter rig tuned 5 kHz off channel, I don't think Doppler is a
big part of the issue.
>What about weight? Weight is not a problem with land mobile but every ounce
>counts on spacecraft/aircraft. Does a comparable NBMF radio weigh more than
>an AM radio? One of the first FM applications were radios on WWII battle
>tanks.
My FM radios are smaller than the AM radios in the aircraft. In fact,
one of the aircraft radio manufacturer's managed to get the aircraft AM
radios smaller by replacing the modulation transformer with a switching
power supply controlled by the modulating signal.
I would expect FM to be smaller than AM. Class C amplifiers are more
efficient and use less power, as well.
Alan
wa6azp
Gary Coffman
>
> I would expect FM to be smaller than AM. Class C amplifiers are more
>efficient and use less power, as well.
I don't disagree with your main points, Alan, but I'd note that typical
AM transmitters use Class C RF stages too. It's just that big plate
modulator that makes them heavy and bulky. As you note, there are
ways around that. FM rigs by constrast are simple and compact, basically
a CW rig with a low level audio stage FMing the carrier oscillator.
The key reasons aircraft aren't going to change to FM are the capture
effect during receive, that can mask emergency calls, the cost of
converting all the FBOs and aircraft nearly simultaneously, due to
the nature of aviation, and spectrum availability, NBFM needs a 20 kHz
channel while AM will fit in 6 kHz.
Gary
--
Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems | we break it. | emory!kd4nc!ke4zv!gary
534 Shannon Way | Guaranteed! | ga...@ke4zv.atl.ga.us
Lawrenceville, GA 30244 | |
Edwin Canning
top
of your commercial FM band.
Michael Friedman
|> In article <36ad3g$8...@unet.net.com> lar...@loren.net.com (Alan Larson) writes:
|> >
|> > I would expect FM to be smaller than AM. Class C amplifiers are more
|> >efficient and use less power, as well.
|>
|> I don't disagree with your main points, Alan, but I'd note that typical
|> AM transmitters use Class C RF stages too. It's just that big plate
|> modulator that makes them heavy and bulky. As you note, there are
|> ways around that. FM rigs by constrast are simple and compact, basically
|> a CW rig with a low level audio stage FMing the carrier oscillator.
*TODAY*, FM rigs are simpler to construct. Back when radios were first
being installed into airplanes FM was much more complex. Not so much
on the transmit side, but rather the receiver. These days you can
buy a complete IF strip with a phase discriminator/detector on one
chip. In the 1930's and 1940's you were consigned to a large rack
of vaccum tubes! AM detectors , by contrast, are usually simple
rectifiers - a one or two tube affair at most.
As for converting to FM today... I think it is simple economics. We
are out of VHF spectrum space to allow the AM and FM systems to exist
side-by-side for transition, and to try to get EVERYONE to switch at
once would never fly.
Disclaimer: FM was invented my a gentleman named Armstrong sometime
in the '30s or '40s, but I can't remember the exact dates, but
it was well after radios were in common use in aircraft. IMO: Modern
AM transceivers are still pretty good, and the gain by converting
to FM would be small.
****************************************************************************
** Mike Friedman, WB2WNX AOPA, EAA, SSA **
** Commercial Glider **
** Instrument Pvt ASEL **
** PA-28-160 N5540W "The Hershey Warrior" **
****************************************************************************
James J Martin
: It's due to a simple fact that AM preceded FM and that AM is what was
: available when airplanes began using radios.
Ever occur to you that two stations transmitting an AM signal at the same
time produce a hetrodyne squeal and that because of the capture effect of
FM a squeal may not always be there? Helps a controller out to know that
more than one aircraft may be calling him and one may be an emergency or
require expeditious handling (doesn't always occur on 121.5 or 243.0).
Works for me.
73 de Jim/WK1V
Retired USAF Air Traffic Controller
Bruce James Robert Linley
>
>Ever occur to you that two stations transmitting an AM signal at the same
>time produce a hetrodyne squeal and that because of the capture effect of
>FM a squeal may not always be there? Helps a controller out to know that
>more than one aircraft may be calling him and one may be an emergency or
>require expeditious handling (doesn't always occur on 121.5 or 243.0).
Well, _narrowband_ FM is really too narrow for the capture effect to work
very well. Listen to your local 2m repeater where all the jammers hang out.
That should give you more than your fill of hetrodyne squeal. If the capture
effect held true, you would only hear one jammer at a time. :) The
capture effect is only significant on wideband FM transmissions.
--
Bruce James Robert Linley ---- lin...@netcom.com ---- Amateur Radio: KE6EQZ
Steven H Philipson
Serge Burjak <se...@systech.mhs.oz.au> wrote:
>MLS has now been discredited and will not be used. GPS approaches are
>being drawn up all over the world.
This overstates the case a bit. MLS hasn't be discredited per se
but rather has been technically passed by. It is still a good system
but it's way too expensive for widespread installation. The cost /
performance for differential GPS (and other advancements) makes it
uneconomical to proceed with widespread use of MLS. Still, there are
MLS sites in use already and there will be more. Some airports and
operators just can't wait for DGPS. That doesn't include most GA
operators though. I'm waiting expectantly for GPS approaches too.
Steve
(the certified flying fanatic)
ste...@shell.portal.com
Andrew W. Tron
by 1997. By that date the upper part of the FM spectrum will be opened
up to broadcasters which will interfere with ILS localizer signals. The
Europeans were counting on widespread adoption of MLS by that date.
However, the FAA has abandoned MLS for at least Cat-I approaches, and
possibly Cat-II and III as well. Furthermore the 1997 deadline does not
apply in North America. Thus trans-Atlantic traffic will face a
potential bind, with incompatible approach aids on opposite sides of
the Atlantic, unless DGPS is available for widespread use by 1997, which
is highly doubtful. Trans-Atlantic traffic might need multimode
receivers (ILS/MLS/DGPS) installed until DGPS becomes the worldwide
standard.
My source for this was an article in "Aviation Leak" issue last month.
Sorry I can't be more specific than that.
--
-------------------------------------------------------------------------------
Andrew Tron at Princeton University | awt...@phoenix.Princeton.EDU
And of the living ... none, not one who truly loves the sky
Would trade a hundred earth bound hours for one that he could fly.
Jeremy Wood
>unless DGPS is available for widespread use by 1997, which
>is highly doubtful. Trans-Atlantic traffic might need multimode
>receivers (ILS/MLS/DGPS) installed until DGPS becomes the worldwide
>standard.
Only one thing wrong with the whole world becomming DGPS...There is a
Military organisation who can selectively turn off GPS, thus putting
'every' (Supposing that we get rid of ILS etc) precision approach out of
action. I think the UK CAA might like the 'expensive' option of MLS,
especially when the weather over this side of the pond so constantly
demands CAT 2/3 equipped A/C for reasonable operation.
>My source for this was an article in "Aviation Leak" issue last month.
>Sorry I can't be more specific than that.
Umm, various editions of Flight International over the past six months.
>Andrew Tron at Princeton University | awt...@phoenix.Princeton.EDU
Jeremy Wood
****************************************************************************
* Jeremy Wood __|__ *
* University of Warwick _____[_]____ *
* Mail es...@csv.warwick.ac.uk o/ \o *
* PPL(A)/IMC/Night and lots of Jump Seat coz you can over here!!! *
****************************************************************************
* Flying because because I'm broke. *
****************************************************************************
p.s Hi uk pilots!!!
Dave Mould
es...@csv.warwick.ac.uk "Jeremy Wood" writes:
> >unless DGPS is available for widespread use by 1997, which
> >is highly doubtful. Trans-Atlantic traffic might need multimode
> >receivers (ILS/MLS/DGPS) installed until DGPS becomes the worldwide
> >standard.
>
> Only one thing wrong with the whole world becomming DGPS...There is a
> Military organisation who can selectively turn off GPS, thus putting
> 'every' (Supposing that we get rid of ILS etc) precision approach out of
> action. I think the UK CAA might like the 'expensive' option of MLS,
> especially when the weather over this side of the pond so constantly
> demands CAT 2/3 equipped A/C for reasonable operation.
> p.s Hi uk pilots!!!
Hello!
According to various electronics trade journals, Inmarsat (a non-military
commercial marine telephone organisation) will be installing
GPS transmitters onboard their next generation of satellites, due to
be launched soonish. They state that they will be far more accurate
than the military ones, and not be subjected to "selective availability"
(deliberate accuracy downgrading), and will also transmit correctional
data for the military sats. If this is the case then the very real argument
against DGPS that you have put forward will fall away.
--
Dave Mould
>>>>>>>> Sig space for rent. Apply within.