Do receiver antennas need matching or not?
billcalley
I always hear that antennas have to be matched to their radio, but
in receivers (such as FM and shortwave radios) I see mostly long
random length antennas used, and these antennas -- be they a
telescoping whip or a long wire out a window -- are used over some
really wide bandwidths. How is this possible if an impedance match
must always be maintained for radios? And since there cannot be a
good match over such wide bandwidths with any (typical) wire antenna,
what is the downside to using these completely unmatched long antennas
for receivers? (Poor gain patterns with lots of nulls? Lower
sensitivity due to bad noise figure or gain match for any LNA or
frontend amp? Degraded overall antenna gain)?
Thanks; I'm very confused on this subject!
-Bill
lt...@yahoo.com
That's one of those "sort of" kind of questions. It depends a lot
on the particular receiver and what frequency range you plan to listen
to, and then on the amount of space you have for an antenna.
In general, receivers that listen to the lower frequency bands, HF
for example, are more sensitive than those that are used for the
higher bands (VHF, UHF, SHF). That means that to hear a typical
signal a specifically designed antenna having the exact output
impedance as the receiver's input impedance isn't required. Almost
anything will work to some extent. The receiver just isn't that
'picky', since it typically has more 'hearing' ability than required.
There's a 'catch' though. Reducing the amount of signal losses in
that 'whatever' antenna is going to make the resulting signal getting
to the receiver that much stronger. Something always nice to have,
but there are practical limits. If that 'whatever' antenna meets your
requirements, then it's as 'good' as anything, sort of. If it
doesn't, then making that antenna less 'lossy' is also nice. That
"less 'lossy'" thingy also includes making it directional, longer,
shorter, higher, whatever, to increase the amount of signal getting to
the receiver. So, looking at it from that point of view, the antenna
ought'a be reasonably 'close' to what will typically 'work' well on
the received frequency. Huge range in that 'close' quality and the
definition of what 'works' means.
There is no 'perfect', 'do everything', antenna. Just too many
factors involved. 'Higher' and 'longer' tends to 'work' better than
'lower' and 'shorter', in general. Which, like any generalization, is
never always true.
That's the sort of 'long', half-assed, technical answer. The
'quick-n-dirty' answer is, no, they don't have to be 'matched' to the
receiver. Which says nothing about transmitters.
- 'Doc
[all puns intended]
Tom Biasi
"billcalley" <billc...@yahoo.com> wrote in message
news:e93d7a93-a8c1-4671...@u10g2000prn.googlegroups.com...
The best transfer of energy is achieved when the antenna impedance matches
the input circuit impedance of the receiver.
This should be the case for the entire band of the desired received signal.
It is not always feasible to do this and it is often not necessary. Today's
receivers have very high gain and excellent selectivity.
They need very small signal strengths to operate and excess signal is
attenuated.
So a piece of wire used as an antenna in an area where the signal strength
is large will not do any worse than a perfectly matched antenna.
In an area where the signal strength is weak (like Mars) matching of the
antenna to the front end of the receiver is desired.
There are other considerations for transmitters.
Tom
Andrew Holme
"billcalley" <billc...@yahoo.com> wrote in message
news:e93d7a93-a8c1-4671...@u10g2000prn.googlegroups.com...
Correct. Those are downsides. The upside is convenience and simplicity.
It's sub-optimal; but it works!
Cecil Moore
> Thanks; I'm very confused on this subject!
The AGC circuit in receivers has enough dynamic
range to compensate for low amplitude signals
from a mismatched HF antenna. The S/N ratio
on HF is mostly external to the receiver.
--
73, Cecil http://www.w5dxp.com
Tim Wescott
> Bill,
> That's one of those "sort of" kind of questions. It depends a lot
> on the particular receiver and what frequency range you plan to listen
> to, and then on the amount of space you have for an antenna.
> In general, receivers that listen to the lower frequency bands, HF
> for example, are more sensitive than those that are used for the higher
> bands (VHF, UHF, SHF).
More correctly, it's _easier_ to make an HF receiver with a good noise
figure, and harder to do so as the frequency goes up.
However, atmospheric noise goes _down_ as the frequency goes up. So for
weak-signal work a receiver designer has a lot of motivation to make
really quiet front ends on VHF and higher equipment. Basically if the
radio is cheap (i.e. if it's for consumer use) then the front end may as
well be made of wood. If the radio is used for long-distance
communication (i.e. microwave links, space communication, some military
or amateur radio) then designers will go to great lengths to get the
noise figure down.
-- snip --
--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com
Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Tim Wescott
In areas where it matters receive antennas are matched, and are something
other than random wire. This is why you can go to Radio Shack and buy TV
antennas* -- they're designed** to be both directional and a good match
over the broad frequency ranges of TV signals.
Get into amateur radio or military communications and you'll find many
different permutations of directional, matched antennas on receive.
Note: For many LNA designs, the best signal/noise ratio occurs at an
impedance that is close to, but not really, a perfect conjugate match.
The signal is coupled to the amplifier best at the conjugate match
impedance, but sometimes the noise is enhanced even more.
* or could -- does Rat Shack still carry antennas?
** kinda -- they're really designed to _look_ like they'd make a good
antenna, but they're better than rabbit ears.
Mark
>
> Note: For many LNA designs, the best signal/noise ratio occurs at an
> impedance that is close to, but not really, a perfect conjugate match.
> The signal is coupled to the amplifier best at the conjugate match
> impedance, but sometimes the noise is enhanced even more.
>
That brings up an intersting question I never did get a good answer
to...
It is my assertion that an LNA that is physically at room temperature
(290K) can have a noise figure no better than 3 dB (i.e. its effective
noise temperature is 290K) IF it is also conjugatly matched i.e.
looks like 50 Ohms.
Yes you can make the noise figure better than 3 dB, but then you must
either cool the device or MISMATCH it to the line.
In other words if it looks like 50 Ohms and it is physically at 290 K,
it's effective noise temperature must also be 290K.
How could it be otherwise?
Comments plese.
Mark
Dave
"Tom Biasi" <tomb...@optonline.net> wrote in message
news:47dbc133$0$5644$607e...@cv.net...
>
> "billcalley" <billc...@yahoo.com> wrote in message
> news:e93d7a93-a8c1-4671...@u10g2000prn.googlegroups.com...
>> Hi All,
>>
>> I always hear that antennas have to be matched to their radio, but
>> in receivers (such as FM and shortwave radios) I see mostly long
>> random length antennas used, and these antennas -- be they a
>> telescoping whip or a long wire out a window -- are used over some
>> really wide bandwidths. How is this possible if an impedance match
>> must always be maintained for radios? And since there cannot be a
>> good match over such wide bandwidths with any (typical) wire antenna,
>> what is the downside to using these completely unmatched long antennas
>> for receivers? (Poor gain patterns with lots of nulls? Lower
>> sensitivity due to bad noise figure or gain match for any LNA or
>> frontend amp? Degraded overall antenna gain)?
>>
>> Thanks; I'm very confused on this subject!
>>
>> -Bill
>
> The best transfer of energy is achieved when the antenna impedance matches
> the input circuit impedance of the receiver.
OH NO! now you have done it! i hope cecil doesn't see this or you have just
openend another endless energy sloshing around thread! what does happen if
the antenna isn't matched to the radio? where does the mismatch energy
go???
Richard Clark
<billc...@yahoo.com> wrote:
>How is this possible if an impedance match
>must always be maintained for radios?
Hi Bill,
It is not always needed if the signal is strong enough. If the signal
is not strong enough, then you can obtain considerable gain through
tuning.
Tuning also brings other advantages by rejecting signals that could
depress your radio's sensitivity.
73's
Richard Clark, KB7QHC
Joop
>> The best transfer of energy is achieved when the antenna impedance matches
>> the input circuit impedance of the receiver.
>
>OH NO! now you have done it! i hope cecil doesn't see this or you have just
>openend another endless energy sloshing around thread! what does happen if
>the antenna isn't matched to the radio? where does the mismatch energy
>go???
>
Less of the energy is "taken" from the received EM field.
Joop
Jeff Liebermann
wrote:
>This is why you can go to Radio Shack and buy TV
>antennas* -- they're designed** to be both directional and a good match
>over the broad frequency ranges of TV signals.
I once cranked out an NEC2 model of a Radio Shock TV antenna to see
what it really did over the 54-890MHz range. It was fairly horrible.
There were actually a few frequencies where the impedance was close to
300 ohms. There were also a few frequencies where it actually had
some gain. At some frequenies, it had more gain in the reverse
direction than forward. As an example of a "directional and a good
match" antenna, that typical Radio Shock TV antenna doth truly suck.
I'll see if I can find the model. Unfortunately, it may have been on
a hard disk that crashed a few years ago.
Not having a good match between the antenna and LNA has several
effects. The mismatch will affect the system noise figure thus
reducing sensitivity. Some LNA's are not unconditionally stable and
will oscillate when presented with a weird source impedance. At HF
frequencies, the atmospheric noise level is above the receiver input
noise level, so considerable mismatching can be tolerated. About
about 20MHz, this is no longer the case, and a match is required.
Antennas are also affected by their load impedance. A highly
directional yagi antenna pattern can easily be ruined by mismatched
coax or LNA input impedance. For the antenna to work as advertised,
it has to see the rated load.
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Phil Hobbs
A good deal of it is re-radiated by the antenna.
Cheers,
Phil Hobbs
AndyS
billcalley wrote:
> Hi All,
>
> I always hear that antennas have to be matched to their radio, but
> in receivers (such as FM and shortwave radios) I see mostly long
> random length antennas used, and these antennas -- be they a
> telescoping whip or a long wire out a window -- are used over some
> really wide bandwidths. How is this possible if an impedance match
> must always be maintained for radios
Andy writes:
As a practical matter, if the background noise heard in the receiver
increases when the antenna is attached, the antenna is good enough.
This means that the atmospheric noise, in the frequency range that
the receiver is tuned to, is greater than the internal receiver
noise....
It also means that any signal that is to be received that exceeds
the
atmospheric noise, will be heard......
Unless you are using some signal processing that can detect signals
below the atmospheric noise level, this is a very good rule of
thumb....
Consider an airborne LORAN antenna, used on aircraft, to receive
100 khz signals. It works out that around 22 inches is the length
where
the atmospheric noise exceeds the general receiver noise for most
receivers. Making the antenna longer will pick up more desired
signal,
but also more atmospheric noise, in the same ratio.....so the SNR
doesn't
get much better. Note that a matched antenna for 100khz will be
many many hundreds of feet long.... but is never used either in boats
or airplanes, since a "matched" antenna serves no advantage to
sensitivity ( SNR)....
These are rules of thumb, and useful approximations, but, in
effect,
you don't need a great antenna unless you are trying to receive a weak
signal....or have a method to increase the SNR by signal processing.
Andy in Eureka, Texas W4OAH
AI4QJ
"billcalley" <billc...@yahoo.com> wrote in message
news:e93d7a93-a8c1-4671...@u10g2000prn.googlegroups.com...
For a receive antenna, you don't need to worry as nearly as much about an
impedance match as you do with a transmitter. You are dealing with much
higher gain on the input side as you are on the output side.
David G. Nagel
Bill;
I haven't looked at the back of a radio in a long time, but those that I
have looked at usually had a trimmer capacitor that helped tune the
antenna to the radio input. This is the impedance match you are looking at.
Dave WD9BDZ
Phil Hobbs
possible? (Hint: the fluctuation-dissipation theorem only applies to
systems in thermodynamic equilibrium. The moment you turn on the power,
that assumption is violated, just as it is in your domestic refrigerator.)
An ordinary room-temperature diode has a noise temperature of 150K
(Tambient/2) as you can show in about 3 lines of algebra, starting from
the diode equation and the shot noise and Johnson noise formulas.
Cheers,
Phil Hobbs
Cheers,
Phil Hobbs
Bill Bowden
Well, I 'm not an expert, but it seems that with a transmitting
antenna, the idea is to transfer as much power as possible to increase
efficiency, and so the antenna needs to be closely matched to the
output of the transmitter for best results. But the receiving antenna
is a different problem, since no power from the antenna is needed to
drive the receiver, and so who cares about the match? The idea with
the receiving antenna is to get the most voltage and highest S/N ratio
with no load. The input to the receiver should be buffered with a high
impedance FET amplifier, or some such, so the receiver draws almost no
power from the antenna. This leaves you free to design the antenna and
input tuning circuit for the highest Q and lowest noise figure without
worrying about impedance match.
Just my opinion.
-Bill
Fred Bloggs
Jeff Liebermann wrote:
> Antennas are also affected by their load impedance. A highly
> directional yagi antenna pattern can easily be ruined by mismatched
> coax or LNA input impedance. For the antenna to work as advertised,
> it has to see the rated load.
>
Ummmmm, cause and effect mismatch there, care to explain how load
mismatch affects directivity? You must be using an apparent directivity
at signals near the sensitivity threshold??
Fred Bloggs
Never mind, I see you are talking about a Yagi with all that radiator
crap...I can see that getting messed up...
Jeff Liebermann
wrote:
>Fred Bloggs wrote:
Ok, you got it. However, mis-terminating any antenna will have some
effect on its pattern. It may not be noticed at low (HF) frequencies,
where the pattern is rather broad to begin with, but it sure has an
effect at VHF and up. In general, the more narrow band and
directional the antenna, the more critical the matching.
The next obvious question is how close duz it have to be? Well, it
again depends on the antenna. For high gain, high freq, narrow band,
and highly directional, it needs a good match to keep from wrecking
the pattern. Most everything else is less critical. My guess(tm)
is that anything up to about a 2:1 mismatch is tolerable.
I like to use 75 ohm coax on 50 ohm antennas and radios. Guaranteed
1.5:1 mismatch.
<http://www.qsl.net/n9zia/wireless/75_ohm_hardline.html>
However, it works just fine for most applications that aren't trying
to squeeze every last bit of performance out of the system.
If you happen to have a vector impedance meter (HP4815A or later), you
can see how well matched the front end of a receiver really is.
Methinks you'll find that most commercial radios are quite good, while
much (not all) consumer electronics (AM/FM, TV, scanners) are not even
close.
Jeff Liebermann
wrote:
>Consider an airborne LORAN antenna, used on aircraft, to receive
>100 khz signals. It works out that around 22 inches is the length
>where
>the atmospheric noise exceeds the general receiver noise for most
>receivers. Making the antenna longer will pick up more desired
>signal,
>but also more atmospheric noise, in the same ratio.....so the SNR
>doesn't
>get much better.
Agreed. However, the short 18" antenna is commonly used for handheld
and aircraft Loran receivers. However marine Loran antennas are
typically 8ft long.
<http://shakespeare-marine.com/antennas.asp?antenna=5220>
That's not the only reason that Loran antennas are rather short. If
the antenna were longer, the impedance would increase, causing it to
pickup more percipitation static, atmospheric noise, and 60Hz
harmonics. A longer antenna would also not be as narrow band and low
impedance as a short (loaded) antenna. The relatively narrow
bandwidth is helpful for eliminating broadcast, beacon band, and other
forms of interference.
Incidentally, that's also one reason why some remote Loran systems
have a pre-amp that really burns some watts. It needs to handle the
out of band overload and stay linear. If the antenna were made
longer, the amplifier would need to handle proportionately more power
(and probably melt). Some details in the patent at:
<http://www.google.com/patents?id=ONUrAAAAEBAJ&dq=4875019>
The "background" section is worth reading. The other reason for the
amplifier is to give the antenna system a 50 ohm output impedance so
that cheap coax can be used.
Jeroen Belleman
>> Note: For many LNA designs, the best signal/noise ratio occurs at an
>> impedance that is close to, but not really, a perfect conjugate match.
>> The signal is coupled to the amplifier best at the conjugate match
>> impedance, but sometimes the noise is enhanced even more.
>>
>
> That brings up an intersting question I never did get a good answer
> to...
>
> It is my assertion that an LNA that is physically at room temperature
> (290K) can have a noise figure no better than 3 dB (i.e. its effective
> noise temperature is 290K) IF it is also conjugatly matched i.e.
> looks like 50 Ohms.
>
> Yes you can make the noise figure better than 3 dB, but then you must
> either cool the device or MISMATCH it to the line.
>
I make amplifiers with 50 Ohms input impedance and 300pV/rtHz input-
referred noise. By your assertion, that should have been impossible.
The trick is that the input impedance obtained by feedback: The
cooled resistor trick. It works.
Jeroen Belleman
dirsk...@gmail.com
Do you want access to China's massive pool of electronic
manufacturers... but lack the time to contact suppliers, negotiate
contracts, arrange shipping or monitor product quality? Don't worry -
Let seriouswholesale deal with all that for you.
*Check out the huge range of Gadgets, MP3 / MP4 Players, Car DVD /
Audio, and Computer Accessories now by visiting the online wholesale
catalog at seriouswholesale. com You'll have peace of mind thanks to
the seriouswholesale Quality Control, 12-month Warranty on all
products, and easy secure payment by credit card through Paypal.
Selling on eBay or your own online store? Send products direct from
our warehouse to your customers using our unique drop-shipping
service. You can profit by selling hundreds of different products,
without holding any of your own inventory! Any questions you have will
be answered by the seriouswholesale English-speaking customer support
team... Their aim is to make your China electronics importing business
easier to run than ever before.
Welcome to http://www.seriouswholesale.com.
seriouswholesale - Buy from the source, profit without the hassle.
- 12 Months Warranty - No minimum order restrictions - Drop-shipping
with no additional fee - Pay by safely by PayPal seriouswholesale
Wholesale Co., Ltd.: Chinas original and best online electronics
wholesaler & drop-shipper: seriouswholesale. com
Joel Koltner
news:HpudnT_1wuk3Q0ba...@web-ster.com...
> * or could -- does Rat Shack still carry antennas?
Yes. If anything there's been a bit of a rebirth in antenna sales as people
start hearing about free over-the-air (ATSC) HDTV.
(Speaking of HDTV... Fry's is advertisiting ATSC->NTSC converters for $59,
coming very close to the $49 I was predicting a while or so ago... Joerg will
be pleased. :-) )
Joel Koltner
news:77dbb0b5-3c5d-4ff8...@u10g2000prn.googlegroups.com...
> As a practical matter, if the background noise heard in the receiver
> increases when the antenna is attached, the antenna is good enough.
This implies only that the antenna/receiver *matching* is good enough... yes?
(I'm thinking that you would still sometimes prefer a highly directional
antenna over just a dipole even though both increase the background noise.
I.e., in both cases the antenna matching is good enough, but without the
directionality the antenna itself might not be good enough to eliminate
interference, overloading, etc. from sources other than the one you're
interested in.)
David Harmon
"Joel Koltner" <zapwireD...@yahoo.com> wrote,
>(Speaking of HDTV... Fry's is advertisiting ATSC->NTSC converters for $59,
>coming very close to the $49 I was predicting a while or so ago.
I saw two models at Wal-Mart for $49 each. Magnavox and some other
name I don't know. That comes even closer.
Cecil Moore
AI4QJ
"Joel Koltner" <zapwireD...@yahoo.com> wrote in message
news:GoxDj.22598$Uf4....@en-nntp-08.dc1.easynews.com...
Over the air HDTV is superior to cable and satellite HDTV. They may sell
more outdoor antennas as soon as it becomes clear that, from the 1996
telecommunications, not only did the FCC ruling on small satellite dishes
overrule the homeowner association covents restricting dsmall satellite
antennas, they ALSO overruled covenants restricting outdoor TV (i.e.yagi
type) antennas...this was done to promote fair competition for cable,
satellite and broadcast TV. I did put up a regular radio shack yagi style
outdoor TV antenna back then and the HOA did contact their lawyer and found
they could do nothing about it. If I ever splurge and buy my 1080p, I will
do it again because the OTA picture is absolutely the best.
AI4QJ
Paul Hovnanian P.E.
>
[snip]
> Over the air HDTV is superior to cable and satellite HDTV. They may sell
> more outdoor antennas as soon as it becomes clear that, from the 1996
> telecommunications, not only did the FCC ruling on small satellite dishes
> overrule the homeowner association covents restricting dsmall satellite
> antennas, they ALSO overruled covenants restricting outdoor TV (i.e.yagi
> type) antennas...this was done to promote fair competition for cable,
> satellite and broadcast TV. I did put up a regular radio shack yagi style
> outdoor TV antenna back then and the HOA did contact their lawyer and found
> they could do nothing about it. If I ever splurge and buy my 1080p, I will
> do it again because the OTA picture is absolutely the best.
>
> AI4QJ
Put up one of these: http://www.digitalhome.ca/ota/superantenna
A home brewed double Gray-Hoverman. Apparently, they work pretty well
and if you build a really impressive one, the HOA will really get their
panties in a bunch.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
The only tools one needs in life:
WD-40 to make things go and duct tape to make them stop.
Jeff Liebermann
<pa...@hovnanian.com> wrote:
>AI4QJ wrote:
>>
>[snip]
>
>> Over the air HDTV is superior to cable and satellite HDTV. They may sell
>> more outdoor antennas as soon as it becomes clear that, from the 1996
>> telecommunications, not only did the FCC ruling on small satellite dishes
>> overrule the homeowner association covents restricting dsmall satellite
>> antennas, they ALSO overruled covenants restricting outdoor TV (i.e.yagi
>> type) antennas...this was done to promote fair competition for cable,
>> satellite and broadcast TV. I did put up a regular radio shack yagi style
>> outdoor TV antenna back then and the HOA did contact their lawyer and found
>> they could do nothing about it. If I ever splurge and buy my 1080p, I will
>> do it again because the OTA picture is absolutely the best.
>>
>> AI4QJ
>Put up one of these: http://www.digitalhome.ca/ota/superantenna
Nice. Too bad it only goes from about 400-800MHz, which covers the
UHF channels. It doesn't work for the VHF channels. Looking at the
4NEC2 plots, it's not very good on VSWR, has reasonable gain, but only
on the lower UHF channels (no problem because the higher channels are
being auctioned off by the FCC).
<http://www.qsl.net/va3rr/hdtv/hoverman.htm>
>A home brewed double Gray-Hoverman. Apparently, they work pretty well
>and if you build a really impressive one, the HOA will really get their
>panties in a bunch.
The local OTA digital TV is on Channel 8 (KSBW) at roughly 87MHz. The
reflector of a suitable Gray-Hoverman antenna should be about 1.5
meters wide. I think the aesthetics committee will be banging on the
front door rather quickly. What's that giant fly swatter doing on the
roof? I wonder if a TV antenna can legitimize a solar cell array if
the array is mounted on the TV antenna?
"Comparing some commercially available antennas"
<http://www.hdtvprimer.com/ANTENNAS/comparing.html>
I really like the negative gain (i.e. loss) in some of the commercial
VHF antennas. Too bad they didn't run antenna patterns, as many such
TV yagis have more gain in the reverse direction, than forward.
Incidentally, I once built a vertically polarized omnidirectional OTA
TV antenna intended as a disguise antenna (if you consider a 2.5 meter
white fiberglass pipe to be suitable disguise). It worked well enough
from about Channel 8 to about Channel 47. Not much gain (about 4dbi)
but the big problem was that it was prone to receiving ghosts
(reflections). I should probably resurrect the design, rename it
"Ultimate Digital Disguise Magic Super-Antenna", and join the hype
instead of fighting it.
Paul Hovnanian P.E.
Does your HOA forbid solar arrays? Some of them can be pretty anal
retentive. Mine won't let me put up my thermonuclear clothes dryer. :-(
> "Comparing some commercially available antennas"
> <http://www.hdtvprimer.com/ANTENNAS/comparing.html>
> I really like the negative gain (i.e. loss) in some of the commercial
> VHF antennas. Too bad they didn't run antenna patterns, as many such
> TV yagis have more gain in the reverse direction, than forward.
>
> Incidentally, I once built a vertically polarized omnidirectional OTA
> TV antenna intended as a disguise antenna (if you consider a 2.5 meter
> white fiberglass pipe to be suitable disguise). It worked well enough
> from about Channel 8 to about Channel 47. Not much gain (about 4dbi)
> but the big problem was that it was prone to receiving ghosts
> (reflections). I should probably resurrect the design, rename it
> "Ultimate Digital Disguise Magic Super-Antenna", and join the hype
> instead of fighting it.
Ghosts are a big problem where I live. Or multipath and the resulting
dropouts the case of DTV broadcasts. That's why I like highly
directional designs (both horizontally as well as vertically). Other
than that, I can get all of our local stations with rabbit ears and a
UHF loop.
All of our DTV stations broadcast on UHF as the VHF band in the Seattle
area is pretty much filled up with the legacy analog stuff. I'm not
certain what the stations plan on doing once the digital cut over is
complete. They might move their digital signal down onto their analog
slot or abandon the analog slot altogether. That will be a factor in
what kind of antenna I put up.
> --
> Jeff Liebermann je...@cruzio.com
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 http://802.11junk.com
> Skype: JeffLiebermann AE6KS 831-336-2558
--
Paul Hovnanian pa...@hovnanian.com
-----------------------------------------------------------------------
Procrastinators: The leaders for tomorrow.
dirsk...@gmail.com
dirsk...@gmail.com
Jeff Liebermann
<pa...@seanet.com> wrote:
>Does your HOA forbid solar arrays? Some of them can be pretty anal
>retentive. Mine won't let me put up my thermonuclear clothes dryer. :-(
No home owners association in my neighborhood. (However, I am the
self-appointed chair person and bill collector for the private road
committee). If we had an HOA, I would be the first to be lynched as I
have 2 dead cars in front of the house, a huge mess ready for
recycling, and an antenna farm on the roof.
However, I have friends that bought into the "planned community"
philosophy and are stuck with CC&R's from hell. Basically, anything
that can be seen from ground level is unacceptable. In the CC&R's
I've read, solar arrays are certainly not allowed, especially on the
roof.
<http://www.renewableenergyworld.com/rea/news/ate/story?id=45648>
I've found the local cities and county bureaucracy on behalf of
various homeowners. Batting average is about 50%.
>Ghosts are a big problem where I live. Or multipath and the resulting
>dropouts the case of DTV broadcasts. That's why I like highly
>directional designs (both horizontally as well as vertically). Other
>than that, I can get all of our local stations with rabbit ears and a
>UHF loop.
I live too far away from the local digital TV xmitters to get reliable
reception. My rule of thumb is that if OTA analog TV reception is
marginal, digital TV will be worse.
Highly directional antennas are the right way to eliminate ghosts
(reflections). However, I keep running into problems with f/b (front
to back) ratio problems, where the ghosts are reflected from behind
the antenna. That's where the lower gain, but higher f/b ratio
antennas, such as a barbeque grill backed bowtie array, makes more
sense. My preference is to use single channel narrowband yagi's for
maximum gain, but that gets really ugly as one per channel is
required.
>All of our DTV stations broadcast on UHF as the VHF band in the Seattle
>area is pretty much filled up with the legacy analog stuff.
We have Channel's digital 10 (KSBW) and digital Channel 12 (KNTV)
<http://en.wikipedia.org/wiki/KNTV>
<http://en.wikipedia.org/wiki/KSBW>
I once did a paper design for a trapped yagi, designed solely for
channels 8 and 11 (the analog channels) and no others. It probably
would work, but nobody was interested in buying one.
>I'm not
>certain what the stations plan on doing once the digital cut over is
>complete.
All of them. The station owners would need to be insane not do do
digital. It's a free extra channel with the oportunity to sell
additional services (i.e. data broadcasting).
>They might move their digital signal down onto their analog
>slot or abandon the analog slot altogether. That will be a factor in
>what kind of antenna I put up.
Duh... I never thought to ask the local broadcast engineers what the
channel lineup is going to be after the Feb 17, 2009 fire drill. I'll
ask.
Every day, I go on an extended exercise constitutional. One day, I
decided to count outdoor TV antennas in my mountain neighborhood. My
guess is that I passed about 100 houses and only saw three outdoor
antennas (which looked ancient and inoperative). I'm wondering if
anyone watches OTA TV in my area.
--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 je...@comix.santa-cruz.ca.us
# http://802.11junk.com je...@cruzio.com
# http://www.LearnByDestroying.com AE6KS
Jim Thompson
wrote:
>On Tue, 18 Mar 2008 10:54:25 -0700, "Paul Hovnanian P.E."
><pa...@seanet.com> wrote:
>
[snip]
>
>However, I have friends that bought into the "planned community"
>philosophy and are stuck with CC&R's from hell. Basically, anything
>that can be seen from ground level is unacceptable. In the CC&R's
>I've read, solar arrays are certainly not allowed, especially on the
>roof.
><http://www.renewableenergyworld.com/rea/news/ate/story?id=45648>
>I've found the local cities and county bureaucracy on behalf of
>various homeowners. Batting average is about 50%.
>
[snip]
Check your state laws, solar is allowed, period, here in AZ...
irrespective of HOA regulations.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
Jeff Liebermann
<To-Email-Use-Th...@My-Web-Site.com> wrote:
>On Tue, 18 Mar 2008 16:25:02 -0700, Jeff Liebermann <je...@cruzio.com>
>wrote:
>
>>On Tue, 18 Mar 2008 10:54:25 -0700, "Paul Hovnanian P.E."
>><pa...@seanet.com> wrote:
>>
>[snip]
>>
>>However, I have friends that bought into the "planned community"
>>philosophy and are stuck with CC&R's from hell. Basically, anything
>>that can be seen from ground level is unacceptable. In the CC&R's
>>I've read, solar arrays are certainly not allowed, especially on the
>>roof.
>><http://www.renewableenergyworld.com/rea/news/ate/story?id=45648>
>>I've found the local cities and county bureaucracy on behalf of
>>various homeowners. Batting average is about 50%.
>>
>[snip]
>Check your state laws, solar is allowed, period, here in AZ...
>irrespective of HOA regulations.
> ...Jim Thompson
The State of Schwarzenegger has had a "Solar Right Act" since 1978.
See:
<http://www.sandiego.edu/epic/publications/documents/070123_RightsActPaperFINAL.pdf>
The Calif Civil Code Section 714 limits the power of HOA's and
governments to restrict solar installations.
<http://www.akeena.net/cm/About_Solar_Power/California_Civil_Code_714.html>
The problem is that term there seems to be some variations in what
constitutes "reasonable restrictions" which are allowed by the law. If
the purpose of the CC&R's is to maintain some semblance of aesthetic
integrity, the local courts have ruled it "reasonable" for them to
block the installation of just about anything with a visual impact.
The interpretation of "reasonable" varies in different jurisdictions
but locally, it seems almost random.
Incidentally, I've read CC&R's that were apparently written perhaps 50
years ago. They're full of restrictions based on race, color,
ethnicity, and such, which are obviously unenforceable. The buyers
were told that that the old contract is good enough because anything
that's illegal won't be enforced. These contracts tend to also have
very broad clauses blocking "anything with an aesthetic impact" and
such, which is where the solar prohibition originated. One contract
I've read itemized examples of prohibited installations, which
included all forms of antennas and mentioned solar panels.
Locally, one planning department imposed some siting and support
structure restrictions that effectively prevented installing of any
solar panels. That apparently was accidental, but it took a year and
an expensive legal action to get them to admit that they goofed.
One homeowner wanted a variance to install the solar panels very close
to the property line. No CC&R's. The variance was denied because of
neighbors protests. It went to court and he lost. Another tried to
get his radio tower approved on the basis of it providing supports for
his tower mounted solar panels. That also was denied.
David Harmon
Moore <nos...@w5dxp.com> wrote,
>
>Does Walmart honor the $40 coupon
Duh.
Claude
an antenna coupler that matches the impedance to the selected frequency. If
a coupler fails we can barely throw a signal a few miles whereas when the
coupler does it's job we can bounce a signal off of the ionosphere at night
for a few thousand miles.
Claude
Montreal
"billcalley" <billc...@yahoo.com> wrote in message
news:e93d7a93-a8c1-4671...@u10g2000prn.googlegroups.com...
Dave Platt
>an antenna coupler that matches the impedance to the selected frequency. If
>a coupler fails we can barely throw a signal a few miles whereas when the
>coupler does it's job we can bounce a signal off of the ionosphere at night
>for a few thousand miles.
That's certainly true at the transmitting end. A good impedance match
is needed in order to enable the transmitter to deliver power
effectively into the antenna, from whence it can be radiated.
It's rather less true at the receiving end, at least in the lower-
frequency HF bands. In these bands, the ability to receive a usable
signal is often dominated by the amount of natural and man-made noise
in the band, and not by the receiver's own self-generated noise. Even
with a serious impedance mismatch between the antenna and the
receiver, enough signal reaches the receiver front-end to overcome the
receiver's own internal noise.
If you happen to live in an area which is blessed by a very low
background-noise level (e.g. out in the country, away from power
lines) and you're DXing in the HF bands, then a good impedance-matched
antenna will let your receiver take best advantage of the low noise
level.
If you're SWLing in a city, surrounded by power lines and electric
motors and neon lights and computers, the background noise level is
going to be much higher, and the weak distant stations will be drowned
out by the noise anyhow... and an inefficiently-matched antenna such
as a whip or longwire will give you enough signal to hear the stations
which are _not_ drowned out by the noise.
As an example - if your receiver has decent sensitivity, and a low
internal noise level, you may find that you can hear a signal with
decent audio quality all the way down to S0 or below (if there's no
noise obscuring it). You then find that with an impedance-matched
antenna the band's background noise is S6 or so. Assuming that you
can make use of a signal which is somewhat below the broadband noise
level, let's say that you decide you can copy stations whose own
individual signals are S5 or better, and that lower-level signals are
blanketed by the noise.
At this point, you realize that you can use an antenna which is 5
S-points (nominally, 30 dB) less efficient, and still receive the same
set of stations. With a less efficient antenna, the stations' signals
will be weaker... but so will the external band noise, by the same
ratio, and thus the signal-to-noise ratio of each station will remain
unchanged.
As an example, my ARES/RACES group has a multiband HF setup in our
city's police and fire admin building, which is downtown near the main
commercial-and-restaurant street and the light-rail system. We have a
trap-dipole antenna strung up above the building's roof. On the
80-meter band, the broadband noise level across the whole band is
rarely less than S9! We could probably receive the same set of
stations using an antenna consisting of two coat-hangers and some damp
string!
--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Mark
>
> - Show quoted text -
good point thanks
Mark
AndyS
Joel Koltner wrote:>
> This implies only that the antenna/receiver *matching* is good enough... yes?
>
*** No, it says nothing about the matching. It only says that the
signals
coming down the antenna from the cosmos are greater than the receiver
noise. If the antenna is matched to the receiver, whatever is picked
up
will be more efficiently fed into the receiver, resulting in a still
higher level.
If the antenna is not matched, well, there may be a heck of a lot of
both noise and signal, and even unmatched the results are strong
enough to override the rx noise..... One caveat , tho, ... in some
conditionsm,
a matched receiver input results in a higher receiver noise level....
not much,
but enough for purists to argue the point incessantly :>))))) .
> (I'm thinking that you would still sometimes prefer a highly directional
> antenna over just a dipole even though both increase the background noise.
> I.e., in both cases the antenna matching is good enough, but without the
> directionality the antenna itself might not be good enough to eliminate
> interference, overloading, etc. from sources other than the one you're
> interested in.)
**** Of course, and a good point..... I was only talking about desired
signal
and atmospheric noise.... If there is a coherent interferer, then
that's a
whole 'nuther thang...... :>)))
Andy W4OAH
Buck
<billc...@yahoo.com> wrote:
>Hi All,
>
> I always hear that antennas have to be matched to their radio, but
>in receivers (such as FM and shortwave radios) I see mostly long
>random length antennas used, and these antennas -- be they a
>telescoping whip or a long wire out a window -- are used over some
>really wide bandwidths. How is this possible if an impedance match
>must always be maintained for radios? And since there cannot be a
>good match over such wide bandwidths with any (typical) wire antenna,
>what is the downside to using these completely unmatched long antennas
>for receivers? (Poor gain patterns with lots of nulls? Lower
>sensitivity due to bad noise figure or gain match for any LNA or
>frontend amp? Degraded overall antenna gain)?
>
>Thanks; I'm very confused on this subject!
>
>-Bill
In a short answer to your question, NO!
The finals won't burn out as there are none and you won't be feeding
radiation into your room.
However, as you probably noticed from the FM radio with the extendable
antenna, you sometimes get a better signal when you extend the antenna
nd move it to the right location.
A good (and matched) antenna may allow you to receive signals you
could not have received with a random length antenna.
Most radios that I have seen usually have a matching network built in
to match the antenna that comes with the radio. In most cases they
aren't that elaborate, just a small coil and a trimmer capacitor.
My father learned that as great as his 50 foot long copper wire worked
for listening to his favorite short wave broadcasts, the signals
improved immensely when I installed an fan-dipole for his three
favorite bands. Did he 'need' that antenna? no, he could hear his
stations without it, but the signal strength was improved and he was
able to pick up more stations.
Dad also ordered an antenna tuner kit, assembled it and attached it
to his 50 foot wire. He found a great improvement in signal strength
using the tuner, almost equal to the multi-band dipole I installed.
Signal to noise ratio are not synonymous with gain. One can have a
lower-gain antenna with high s/n that outperforms a higher-gain
antenna with low s/n. When it gets critical, the s/n can be the
determining factor as to whether you receive intelligent communication
or not.
You are probably digging for technical, theoretical information more
than practical, but just in case...
If you look in stereo magazines, you seldom see radio ads bragging
about how much better they receive than the competition. If you look
in Ham magazines, that's a very important feature. Most consumers are
looking for stereos that play music well and they listen to local
stations. Most ham operators want to pull that weak signal out of the
noise to make the contact.
Just some thoughts.
Hope this is helpful to someone.
Buck
N4PGW
--
73 for now
Buck, N4PGW
"Small - broadband - efficient: pick any two."
Homer J
radio frequency (RF) match yes this would be an ideal situation since
maximum energy transfer occur when Imepdance of the antenna (Zant) =
Imedance of the Receiver Antenna Port (Zrx_port).
All this talk about noise while important to minimum detectable signal more
greatly influenced by the internal Noise Figure (NF) of the receiver (RX).
In my line of work, which is Radar engineering, we use a standard
temperature T = 270 Kelvin to model the noise originating by natural
extgernal sources of which the Sun is the biggest contributor.
The short end answer on HF you will probably not notice a big difference as
long as the antenna is close between a 1/4 to 1/2 wavelength long [e.g.
wavelength = Velocity of Light (C) / Frequency of Operation (Fo)]. However,
if you use one of those collaspable whips found on the portable shortwave
receivers you will. This is because the anyenna impedance is a lot less than
the usual 50 Ohm impedance of the RX antenna port (e.g. Zant << Zrx_port ).
You can match very short antennas with antenna tuners to make them transfer
efficently to the RX antenna port but now the nasty parameter of effective
antenna aperature (square feet or meters) reduces it caoture ability (think
of catching a baseball with and without a glove, the probability of catching
the ball is higher with a glove due to it larger capture area).
Well that is enough to put someone to ZZZzzzzzzzzzz. Hi Hi
73, Homer J
on all lower and upper channels Thane-Fer
Joel Koltner
news:f3ea2$47ef7f68$ce94701c$31...@DIALUPUSA.NET...
> All this talk about noise while important to minimum detectable signal more
> greatly influenced by the internal Noise Figure (NF) of the receiver (RX).
My understanding is that this is not the biggest influence at HF -- there's so
much atmospheric noise down there that even with a pretty poor receiver (noise
figure-wise) the MDS is usually just about the same as with a much better
receiver.
> In my line of work, which is Radar engineering, we use a standard
> temperature T = 270 Kelvin to model the noise originating by natural
> extgernal sources of which the Sun is the biggest contributor.
Have you seen the graph in, e.g., Krauss's antenna or EM book? T=270 is a
poor model at many frequencies. (Granted, if you're doing narrowband designs,
it'll just be some offset error that's probably not too much worse than, say,
+/-3dB.)
> However, if you use one of those collaspable whips found on the portable
> shortwave receivers you will. This is because the anyenna impedance is a lot
> less than the usual 50 Ohm impedance of the RX antenna port (e.g. Zant <<
> Zrx_port ).
> You can match very short antennas with antenna tuners to make them transfer
> efficently to the RX antenna port but now the nasty parameter of effective
> antenna aperature (square feet or meters) reduces it caoture ability
From watching this thread I get the impression that -- at least on HF again --
the (lack of) capture area is the much bigger problem than the mismatch is.
---Joel
LVMarc
Art Unwin
I never knew that "aperature" could be measured in square feet or
metres!
Is there a book that describes it in such a way ?
Art
terryS
> Hi All,
>
> I always hear that antennas have to be matched to their radio, but
> in receivers (such as FM and shortwave radios) I see mostly long
> random length antennas used, and these antennas -- be they a
> telescoping whip or a long wire out a window -- are used over some
> really wide bandwidths. How is this possible if an impedance match
> must always be maintained for radios? And since there cannot be a
> good match over such wide bandwidths with any (typical) wire antenna,
> what is the downside to using these completely unmatched long antennas
> for receivers? (Poor gain patterns with lots of nulls? Lower
> sensitivity due to bad noise figure or gain match for any LNA or
> frontend amp? Degraded overall antenna gain)?
>
> Thanks; I'm very confused on this subject!
>
> -Bill
What has not been mentioned much is that AM band broadcast receivers
and FM band receivers are designed to to tune over a fairly wide band
of frequencies; so very difficult to build antenna that will mtach at
all those different 'wavelengths'.
For example; the broadcast band (North America) is roughly 550
kilohertz (that's 545 metres wavelength) to about 1.7 megahertz (about
176 metres). That's 3:1 ratio!
On FM, 88 to 108 megahertz (3.4 to 2.8 metres) the ratio is less but
still cnsiderable at 1.2:1 So again very difficult to design and build
an 'all frequencies' antenna.
For stations designed to receive only one frequncy the antennae can be
constructed for that only; hence the matching can be as optimum as
possible.
You
<32ac5bd0-2516-4fdd...@u69g2000hse.googlegroups.com>,
terryS <tsan...@nf.sympatico.ca> wrote:
> For example; the broadcast band (North America) is roughly 550
> kilohertz (that's 545 metres wavelength) to about 1.7 megahertz (about
> 176 metres). That's 3:1 ratio!
HOWEVER, if you will look at the Antenna Design for a AM Broadcast
Receiver, using a Ferrite Loop Antenna, you WILL notice that the
Loop IS Tuned to the specific part of the band that the receiver is
being tuned to, by Linked Ganged Variable Capacitors, in the Receivers
Frontend. These designs have been around for MANY years, (1940's anyway)
and are a very mature technology.