Combining two antennas to feed one box? Or an omni-directional? - AVS Forum
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post #1 of 9 Old 09-04-2008, 02:49 PM - Thread Starter
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Is it even POSSIBLE to combine the feeds of two different antennas so that a single digital box is being fed by stations coming at it from two (even slightly) different directions? (Or will that make reception worse?)

Also, in place of that, what are the results of feeding an omni-directional antenna's feed into a digital box? I tried it a long time back with an old "early stages" digital tuner, and wasn't too pleased with the results. Would I get better results now, either due to using a newer omni-directional antenna or due to using a newer box?
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post #2 of 9 Old 09-04-2008, 03:51 PM
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Quote:
Originally Posted by gastrof View Post

Is it even POSSIBLE to combine the feeds of two different antennas so that a single digital box is being fed by stations coming at it from two (even slightly) different directions? (Or will that make reception worse?)

Also, in place of that, what are the results of feeding an omni-directional antenna's feed into a digital box? I tried it a long time back with an old "early stages" digital tuner, and wasn't too pleased with the results. Would I get better results now, either due to using a newer omni-directional antenna or due to using a newer box?

I'm still a bit of a newbie when it comes to outdoor antennas, but I have absorbed quite a bit of info over in our Antenna threads here.

One thing I can tell you is while it's possible to combine two antennas, it is likely less of a hassle for you to use one omnidirectional (or even one directional one with a rotator). From what I understand, the coax from each of the antennas has to be identical in every way, length especially, or you'll get multipath issues, and the same goes for the combiner you use...don't go cheap on the signal combiner.

How far away from your towers are you? Your TVfool.com image/results might be helpful to post. In my own situation, my towers are grouped together in two different directions, almost 180 degrees apart. However, I'm less than 12 miles for almost all of my towers, with the furthest stations being 45 and 60 miles away. I have a large directional antenna aimed in one direction to pull in those stations farther away, and the bonus is directly around my antenna (within 10 miles or so), it behaves multidirectionally. Therefore, I don't even have to move my antenna to pick up the stations I wanna receive, which suits me fine.

If I really wanted to, I could use my rotator to turn and scan for channels, and with my antenna being a large directional one, I could probably pick up many more stations in other markets within a 100 or more mile radius.

Hope the answer to your question(s) is in there somewhere.
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post #3 of 9 Old 09-04-2008, 05:24 PM
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Quote:
Originally Posted by nwiser View Post

From what I understand, the coax from each of the antennas has to be identical in every way, length especially, or you'll get multipath issues, and the same goes for the combiner you use...don't go cheap on the signal combiner.

True, but if the antennas are aimed at two different sources you may still get screwed because each antenna will be picking up some of the other source in the side lobes of it's antenna pattern, and it can also be pickung up signals reflected off other things which will be out of phase. That fuzzed up signal will be mixed into the good signal and can mess it up.
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post #4 of 9 Old 09-04-2008, 08:18 PM
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It can be done, I have a small antenna pointing WSW and a deep fringe antenna pointing NNW. When I first set them up I combined them using two different lengths of coax from the antennas to the combiner. The coax length difference caused channels 6 and 13 to cancel out between the two antennas. I have tried three antennas combined and could not get it to work.

Philip
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post #5 of 9 Old 09-04-2008, 10:40 PM
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Quote:
Originally Posted by JWD-PEC View Post

It can be done, I have a small antenna pointing WSW and a deep fringe antenna pointing NNW. When I first set them up I combined them using two different lengths of coax from the antennas to the combiner. The coax length difference caused channels 6 and 13 to cancel out between the two antennas. I have tried three antennas combined and could not get it to work.

Philip

That's how you do it, it's phase tuning by adjusting the length. I ran the feed lines in my window and experimented with adding small lengths to get them to tune best.

That doesn't help in cases of multipath where one of the antennas is picking up reflected signal which arrives later in time.
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post #6 of 9 Old 09-05-2008, 08:10 PM
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Quote:
Originally Posted by gastrof View Post

Is it even POSSIBLE to combine the feeds of two different antennas so that a single digital box is being fed by stations coming at it from two (even slightly) different directions? (Or will that make reception worse?)

Also, in place of that, what are the results of feeding an omni-directional antenna's feed into a digital box? I tried it a long time back with an old "early stages" digital tuner, and wasn't too pleased with the results. Would I get better results now, either due to using a newer omni-directional antenna or due to using a newer box?

Omni-directional antennas have very poor gain. So unless youre very near to the transmitters, theyre not a good option.

Combining identical antennas that point in the same direction with a correct phasing line can INCREASE gain about 2.5db. Combining identical antennas that point in different directions can DECREASE gain about 3.5db.

If the stations arent that far apart in degrees and the signals are powerful, pointing the antenna in between the two stations may do the trick.

If not, then you can either get a rotor (the fastest of which has a max rpm of 1) or do what I do, two antennas, two separate downleads feeding into an A-B switch on the tv. Very low losses. (RS has a remote controlled A-B switch)

Another option for just two stations thats probably not very practical for you, is to mount two indentical antennas horizontally, and vary the spacing distance between them to create two separate large lobes. In order to do this effectively, you would have to computer model the two antennas and vary the distances between them in order to find the exact distance needed to get the exact degrees of lobes that you need for your exact location. You can do this by trial and error of course. But be forewarned, at UHF frequencies its harder than adjusting your cars' headlights correctly, heh.
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post #7 of 9 Old 06-10-2013, 08:25 PM
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I attempted combining to directional antennas and got improved reception on certain channels.
HOWEVER.. I actually completely lost NBC and CBS...I believe because of the strong multipath distortion.

I attempted using an omnidirectional antenna ( HD-360 Omnidirectional TV Antenna ) and received all the channels i wanted....BUT Idid lose some signal strength on a few channels due to the fact that it is not directional but at least the job was done.

The omni directional tv antena i am using can be found here: http://nationalantennas.com/store/products/HD%252d360-Omnidirectional-Long-Range-UHF-VHF-HDTV-Outdoor-Amplified-Antenna-Package.html

Also..if you have enough time and energy you can construct an omnidirectional tv antenna yourself ...just search "omnidirectional TV Antenna DIY" on google.

Havent tried that method yet...
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post #8 of 9 Old 06-11-2013, 07:21 AM
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That looks to be a nice antenna with bodacious gain due to its integrated amp. Of course if the signal is weak or experiencing multipath at the antenna the amp may not help much or even make it worse. Sounds like you're fine though. Could try just slightly shifting the direction in the event that those antenna pattern lobes are lining up such that multipath is affecting those few channels.

FYI omni antennae are unity gain. One can crudely think of directional antennae as having increased gain over omni by virtue of slicing up and stuffing a piece of the omni pie.

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post #9 of 9 Old 06-28-2013, 06:53 PM
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