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Old 25-Mar-2013, 12:46 PM   #1
er1cdotnet
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Gain vs. Aperture

Ok, the more I learn the more I get confused!

So I want to pull a UHF signal (channel 23) out of the weeds. It's about 25 miles away at a higher elevation with some summer foliage in between. My first thought was return my DB4e and go with a high gain yagi. After more reading, it appears that I may do better with a larger bowtie style due to the increased aperture.

When does one worry about gain vs. aperture?
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Old 25-Mar-2013, 1:01 PM   #2
elmo
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Be sure to post a link for your location's report.
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Old 25-Mar-2013, 4:44 PM   #3
teleview
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Is this the same reception situation??

http://forum.tvfool.com/showthread.php?t=13038
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Old 25-Mar-2013, 5:21 PM   #4
er1cdotnet
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Elmo,

Thanks for the reply.

Here is the link; http://www.tvfool.com/?option=com_wr...1ddae4fc4eec6b

I guess I am asking about gain vs. apeture to figure out if I want to go with something like a DB8 or a 91XG. Mainly interested in channel 23 (WVPX). I have a DB4e in the attic and it grabs everything (including VHF) just fine, EXCEPT WVPX is nowhere to be found. I figured as long as I have to go to the roof, Im going to throw up something that is overkill so I have elbowroom...
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Old 25-Mar-2013, 5:43 PM   #5
elmo
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Well, as for your question, I'm not sure I can answer that for you. Someone else here who's more of an antenna guru will be sure to give you a knowledgeable answer. I'd only be speculating and don't want to waste anyone's time. I just know that the report will help whoever, esp. so they can see the channel in question.

So I guess the roof isn't a mounting option? Being a 2-edge plus trees, an attic likely just makes that worse. Obviously it's not an issue w/the other channels since they're virtually in your backyard. But given the signal #'s you're showing for WVPX, I'd expect that you'd still be able to pick it up to some degree. I've got a 2-edge with worse #'s plus another 5 miles and some nearby trees with a gap in between em, but I get a fairly steady 60+% on it....but I'm shooting from the roof.
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Old 25-Mar-2013, 5:51 PM   #6
er1cdotnet
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We are in a rent to own house, so I hesitate to start drilling holes in the outside walls (At least until we purchase it!). Im sure the current owners wouldn't mind, but I try to be a good tenant.

Unfortunately, the wife won't let me cut the cord unless she has her ION programs. So until I can "positively" get WVPX, she won't be "positively entertained"
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Old 25-Mar-2013, 6:02 PM   #7
ADTech
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As noted in our emails last week:

You're going to have to go to the rooftop. Be prepared to use a taller mast so that you can experiment with various heights for the antenna. UHF signals that have to "bend" over terrain will tend to form "layers" of hot and cold zones and you're going to have to experiment with the antenna's height to find a "warm" zone.

Visit http://www.hdtvprimer.com/ANTENNAS/siting.html and see the section right after the cartoon.



Going to the 91XG over the DB4e will in no way assure you of success with that ION stations.
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Old 25-Mar-2013, 6:46 PM   #8
er1cdotnet
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Hey ADTech!

::Sigh:: I knew this thread would devolve, that's why my original question was worded the way it was and I did not include much specific detail.

Yes, we now know I have to go to the roof. My question was more educational rather than "Why can't I get my ION???".

Let me rephrase my original question; When (or does) one care about aperture vs. gain when selecting an antenna? If what I am understanding is true, then antenna gain is really only part of the picture when it comes to receiving a signal. Is one favored over another when selecting for different signal strength conditions, environmental conditions, etc?
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Old 25-Mar-2013, 7:38 PM   #9
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One old guy's thoughts and observations

I have seen a few opinions expressed but I've not come across a technical read on this issue that would rise above one persons opinion or anecdot vs another.

My opinion (not backed by anything other than personal experience) is that on average, there is very little if any difference. The panel antenna that works in one application is beaten by a Yagi in another and vise versa. When one is down to differences of 1 or 2 dB and still has no solid lock on a signal, don't expect dramatic differences.

Ken Nist (hdtvprimer) tried building a 16 bay panel and even a 32 bay panel which would have plenty of aperture. his success or failure would not be the final word on the subject, but as I recall he was left to theorize that not all elements were 'illuminated' due to diffraction of the signal. If that theory was accurate, a single Yagi with a few dB less gain may have performed just as well or better.

But if multipath is due to variable conditions (moving reflective surfaces, etc.) neither panel nor Yagi would seem inherently superior to the other.

With out a means to accurately measure the conditions you're left to experiment.

If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper.
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Old 26-Mar-2013, 5:51 PM   #10
er1cdotnet
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GroundUrMast,

Thanks for the information, that is what I was seeking.

I'd seen the Nist picture, but never read up on the history.
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Old 26-Mar-2013, 6:23 PM   #11
GaryArnold
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My experience is the following:

To receive 2Edge (Double edge diffraction) signals, it is generally better to have an antenna with a larger "capture area."

I have compared the Channel Master 4251, a hugh 7-ft. parabolic antenna, with one of the highest gain UHF yagi antennas available - the Winegard HD-9032, on two 2Edge channels (channels 25 and 45), where the transmitter was over 100 miles from me. The results are posted on my website at kvhf.com.

To summarize - UHF signals can significantly vary just inches apart, and even more so with 2Edge signals. In order to receive a signal, it must hit the antenna. While at times the yagi receives an identical signal as the parabolic, at other times the signal misses the yagi while still hitting the parabolic. For a more consistent signal level, the more capture area the better.

For extreme cases, you can get the Antennacraft 16-bay antenna or a high-gain 8-bay antenna where the gain is as high as the best UHF yagis thereby getting the highest gain plus a large capture area.
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Old 27-Mar-2013, 1:31 AM   #12
mtownsend
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Quote:
Originally Posted by er1cdotnet View Post
When does one worry about gain vs. aperture?
In general, gain is the only parameter you need to worry about.

Just because an antenna has a large physical aperture doesn't mean that it's going to have a high effective aperture. See http://en.wikipedia.org/wiki/Antenna...ure_efficiency.

Gain is directly proportional to the effective aperture of an antenna, so essentially, they represent the same thing. However, you should not confuse physical aperture with effective aperture since the aperture efficiency can vary a lot between different antenna designs.

Gain is gain, no matter how it was achieved. With this parameter alone, you can compute how much signal power is going to be delivered to the antenna terminals.

In some cases, you may also want to know the radiation pattern of the antenna. If you have some off-axis interfering signals that you want to block out, you'll want to take a look at where the "side lobes" of the antenna pattern are relative to your desired signal.
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