Winegard HD 7694P vs. HD7697P and antenna gain

[dprljackson]

Hi,

I'm a little confused about something and am hoping someone can help me out. At solidsignal.com, it says the Winegard HD 7694P has an approximate range of 30 miles for high VHF and 25 miles for UHF while the 7697P has an approximate range of 60 miles for high VHF and 50 miles for UHF. The boom length on the 7697P is twice as long as on the 7694P, so it doesn't completely surprise me that the range would be twice as long. However, the gain specs has the 7694P at 8.3 dB for channel 7 and 10.7 dB for channel 50 whereas the 7697P is listed at 10.9 dB for channel 7 and 11.8 dB for channel 50, a difference of between 1-2 dB.

Now, I do realize that antenna "range" is hard to quantify because every place has different buildings, trees, and terrain. However, the gain specs seem to suggest to me that these two antennas are fairly equivalent. Is that correct or am I not understanding something? I guess I'm trying to determine if the 7697P will really perform significantly better (and hence justify the increased cost) than the 7694P.

I guess I don't really understand antenna gain. Being measured in decibels, does that mean a 3 dB increase corresponds to a doubling of the signal strength at the output of the antenna? If so, would that mean that doubling the distance from a source would result in a signal strength that is 1/4 as strong and therefore you would need an antenna with a gain that is 6 dB higher to compensate?

This doesn't add up with the information at solidsignal.com so I must not be understanding something correctly. Any help would be appreciated.

Thanks,
David

[John Candle]

Antennas have different gains across a range of channels. One reason is some reception areas need a little more gain in the channel bands of VHF low 2 thru 6 , VHF high 7 thru 13 , UHF 14 thru 69. Another reason is that Tv antennas are a design compromise. Due to the Extremely Wide range of channels it is not possible to design a tv antenna that is 100 % efficient across all the channels. And as far as the cost of antenna goes , antennas last 5 to 10 years outside that figures out to be 3 to 6 cents per day. And if the antenna is in the attic it might last forever. And it's a good practice to install a antenna thats a little bigger so as to have elbow room when receiving tv transmissions. In good to strong signal areas 1 to 2 dB gain or loss makes no difference. In far fringe or weak signal locations where squeezing out ever last drop of signal strength is important then 2 to 4 dB signal gain can make a difference. Many years ago when analog tv was the only way to receive tv , a test was preformed with signal strength and what is observed on the tv screen. A signal attenuater was used to adj. the signal strength to just above when snow is seen in the picture. A 2 db increase in signal strength and the observers said it ' feels ' like the picture is better. A 4 dB increase and the observers of the picture said I think the picture is better. And 6 dB increase and the observers of the picture said Now That Is A Lot Better. And it is good practice to install a tv antenna that is a little bigger for elbow room for bad weather and day and night reception.

[Dave Loudin]

Originally Posted by dprljackson

I guess I don't really understand antenna gain. Being measured in decibels, does that mean a 3 dB increase corresponds to a doubling of the signal strength at the output of the antenna? If so, would that mean that doubling the distance from a source would result in a signal strength that is 1/4 as strong and therefore you would need an antenna with a gain that is 6 dB higher to compensate?

Thanks,
David

You are correct about decibels. However, the field strength of an electromagnetic wave decays by the square of distance, not linearly.

[dprljackson]

Originally Posted by Dave Loudin

You are correct about decibels. However, the field strength of an electromagnetic wave decays by the square of distance, not linearly.

Yes I know that. That's why I said a doubling of the distance results in a quarter of the field strength. To make up for that factor of 4 drop off, it seems like the antenna would need an additional gain of 6 dB.

So that is why I was confused as to the claims of 25 miles/50 miles for the two different antennas with relatively similar gains (1-2 dB). It would seem to me that in order to claim that an antenna is good at "twice the distance" it would need a gain that is approximately 6 dB more. I'm guessing the one antenna is probably slightly better than 25 miles (maybe 30-35) and the other is slightly worse than 50 miles (maybe 40 or so). That would make more sense.

Thoughts?

[Tower Guy]

Originally Posted by dprljackson

So that is why I was confused as to the claims of 25 miles/50 miles for the two different antennas with relatively similar gains (1-2 dB).

Thoughts?

My thought is to ignore the published range, analyze the predicted signal strengths of the stations that you want to pick up, and select the proper antenna based on that data. Always provide as much margin as feasible (~10 db) to compensate for weather and other factors without wasting $$.

[Dave Loudin]

Originally Posted by dprljackson

Yes I know that. That's why I said a doubling of the distance results in a quarter of the field strength. To make up for that factor of 4 drop off, it seems like the antenna would need an additional gain of 6 dB.

My apologies. I reread your post several times and completely overlooked that you had it right.

As Tower Guy alludes to, the mileage claims are completely subjective estimates by antenna manufacturers. When we didn't have ready access to the data to properly model all the RF paths, this was the best measure available. Now that you can quickly determine antenna gain requirements for reliable reception, you can do the tradeoffs yourself.

[vms]

Yes, I am also wondering about this as well. First of all, are Winegard HD769xP gain specs accurate? I'm wondering if I should get the HD7695P over the HD7694P but if the 7695P's UHF gain is less than 1dB average for UHF, as the specs state, then it doesn't seem worth going up in size to me, if in fact the specs are accurate. Other than dB gain, is there any other reason to have more antenna real estate?

I read people suggesting going up in size if they're going to mount it in the attic to compensate for building loss, but it seems to me that they should go up as many sizes as they can since I think the building loss would be at least 3dB and probably closer to 10dB.

Anyway, I'm going to mount, whichever antenna I decide on, on the roof and I'm wondering if I can get a channel with an NM of 7.9 and LOS(with one, possibly 2 TVs in future) with possibly some far away trees cutting the signal. I don't know how much those trees may cut the signal and if I could get that station anyway.

[John Candle]

dprljackson has Many other posts here at tvfool . Holly Smokes , put an end to the Grief and Misery and go with the HD7698P.

[John Candle]

Attn: VMS it is best to make your own post in the Help With Reception part of tvfool. http://forum.tvfool.com/showthread.php?t=4 . We get Many people that are all tangled up and twisted up and do not know which way to go , it is best to not jump in on another post as the information gets all tangled up.

[mtownsend]

Originally Posted by vms

are Winegard HD769xP gain specs accurate?

I believe that the more reputable antenna manufacturers (the likes of Winegard, Channel Master, and Antenna Direct) will publish gain specs based on actual measured data, so I do trust them to be reasonably honest.

Just keep in mind that these are only approximations to begin with. There may be unit-to-unit variations, and some people do a better job of assembling them than others. If anything is bent, broken, out of place, shorted, disconnected, painted, etc., you may end up with slightly different performance. Other nearby objects (roof, other antennas, buildings, trees, etc.) will also influence the behavior of the antenna.

Use the numbers to estimate how much signal you will have. Then give yourself some extra margin, just in case you need it.

Other than dB gain, is there any other reason to have more antenna real estate?

Antenna gain is probably THE most important factor in your setup. The reason antennas come in so many different sizes is because each situation is different and may have different gain requirements.

Another important antenna quality is the radiation pattern or directionality of the antenna. In general, higher gain antennas have a tighter beam width (gain and directionality are very much related to each other). This can be important when aiming the antenna, or trying to get multiple signals spread in different directions, or if you need to screen out some of the multipath signals bouncing around the environment.

Size and shape may also be important to some people. If your attic space is tight, it's good to have multiple options available so that you can strike the right balance between fit and performance.

I read people suggesting going up in size if they're going to mount it in the attic to compensate for building loss, but it seems to me that they should go up as many sizes as they can since I think the building loss would be at least 3dB and probably closer to 10dB.

Building loss varies by frequency and building material. TV signals can pass through most residential walls pretty easily, but nails, ducts, pipes, wiring, and other objects might get in the way a bit. Aluminum siding, wire mesh in stucco, foil-backed insulation, and similar objects can make it near impossible to get any signal through. Building losses can vary a lot, typically in the range of 1 to 20 dB. Most attics tend to be on the lower end of this range. Since every situation is different, these guidelines should be adjusted accordingly.

Note that going up in antenna size not only gives you more gain, but it also (usually) gives you a tighter antenna beam width. The tighter beam width can help combat the effects of multipath which is more likely to be present in the attic. Gain and directionality work together to improve your chances of picking up a clean signal from inside the attic.

Going too big in the attic can create its own problems too. If the size of the antenna causes it to get too close to other objects (e.g., nails, metal braces, electrical conduit, etc.), the antenna performance may start to change and you don't really get the gain improvements you were expecting. Size might also limit your ability to assemble, mount, and aim the antenna correctly.

In the end, no matter how big you go, and indoor antenna is never going to be as predictable and well understood as an outdoor antenna. Ideally, antennas work best in a completely open space (that's how they were designed to work). Indoor antennas are surrounded by objects that will block, reflect, or interfere with the signals. Nearby metallic objects can change the gain characteristics of the antenna. The surrounding environment can even change from day to day (e.g., wet/dry/snow-covered roof, moisture content in the wood, etc.). The number of variables goes up a lot. Even if attic space it not a problem, indoor antennas always come with a lot more uncertainty.