Do receiver antennas need matching or not?

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.)

On Mon, 17 Mar 2008 09:56:01 -0700 in rec.radio.amateur.antenna, "Joel Koltner" wrote,

I saw two models at Wal-Mart for $49 each. Magnavox and some other name I don't know. That comes even closer.

Does Walmart honor the $40 coupon at:

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:

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.

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

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"

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.

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. :-(

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.

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.

I've found the local cities and county bureaucracy on behalf of various homeowners. Batting average is about 50%.

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.

We have Channel's digital 10 (KSBW) and digital Channel 12 (KNTV)

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.

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).

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.

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:

The Calif Civil Code Section 714 limits the power of HOA's and governments to restrict solar installations.

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.

On Mon, 17 Mar 2008 18:51:33 GMT in rec.radio.amateur.antenna, Cecil Moore wrote,

Duh.

Not sure about the higher frequencies but in the HF band we absolutely need 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

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

=A0

good point thanks Mark

Joel Koltner wrote:>

Andy W4OAH

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

I did not see all the replies nor the original post but in the world of 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

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.

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,

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

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