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Old 8-Jan-2015, 3:45 PM   #1
rickbb
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Advise on combining 2 UHF antennas

Radar plot;

http://www.tvfool.com/?option=com_wr...2c15699c13a677

I realize that an A/B switch would be a better option reception wise, but the other person in the house will have a cow if I make her have to learn how to switch yet another input just to change channels.

The issue is going to be trees this spring. I get channels from 3 main directions. My current antenna is a roof mounted DIY McClapp DB4, no reflector aimed at 130T. I get good reception from all directions on calm days, high wind days do cause some drops on the VHF-HI channel 11 and the closer UHF stations from the 228T direction.

I have 2 large maple trees directly in front of the channels at 228T less than 20 feet from the antenna. Now with no leaves signal quality is good most of the time even being at 90 degrees from where my antenna is aimed. But I’m sure this spring I will lose them when the leaves come out.

I have 2 places where I can mount the antenna. If I move it to the other side of the roof I can clear the trees from 228T but start getting blocked from the 120T direction. Adding a taller mast to clear the trees would need to be 20 feet taller or more and need guy wires. This will also cause the aforementioned other person in the house to have the aforementioned cow.

I was thinking about making another bow tie with a reflector, and smaller like a DB2 and aiming it at the 228T direction. Would it being directional and smaller help reduce problems with trying to combine them?
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Old 8-Jan-2015, 10:34 PM   #2
GroundUrMast
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Would it being directional and smaller help reduce problems with trying to combine them?
Usually, no. If you are trying to use an unfiltered splitter in reverse as the combiner, your best hope for some success is to use identical antennas. Attempting to combine dissimilar antennas is wildly unpredictable due to the variations in gain and impedance of each.

If you can't 'sell' an axillary tuner or A/B switch, you may be forced to spend some money on tuned filters that cover the channels of interest. Tinlee.com can build a tuned combiner based on your specific situation. Custom solutions aren't free.
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Old 8-Jan-2015, 11:34 PM   #3
Jake V
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Given Rick's radar plot, here's a question for the experts:

What about a DB-8E, with one panel having the reflector removed aimed at 342 degrees magnetic (to get the NNE and SE signals) and the other one aimed at 263 degrees (SW)? And maybe a CS600 for the PBS station on real channel 3 at 342 degrees or, if he wanted the ABC on real channel 11 a Y10713 aimed at 128 degrees. Or would the fact that many of them are 2 edge in the teens and single digit power levels make that impossible/unlikely?
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Old 9-Jan-2015, 12:20 AM   #4
GroundUrMast
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Or would the fact that many of them are 2 edge in the teens and single digit power levels make that impossible/unlikely?
I wouldn't guaranty success but I certainly wouldn't say 'impossible' either.

I think that your proposed solution is spot on for an off the shelf type customer... If the reflector is treated carefully, it can be reinstalled if the single modified UHF antenna proved to be unable to deliver acceptable performance. One could then opt to add another UHF antenna and the necessary filter/combiner network(s).
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Old 9-Jan-2015, 4:33 PM   #5
rickbb
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I will have to ponder on it some more, I have until April before it becomes an issue.

What Jake has suggested is sort of what I was thinking of, only a home made version. The only problem with a AD DB8e is the 2 panels of bow ties are mounted on the same mast. I need them to be about 16 feet apart to get around the trees.

I have another DB4 made up already, (I kind of like making them). I will work on adding a reflector to it and get a quote on a tuned combiner. I understand that they are not cheap or quick to get.

I'm not really interested in real channel 3 as I already get 2 sets of PBS stations. And I will probably add a VHF to get channel 11 better if it becomes an issue later, for now it's fine.

Another thought, the 2nd antenna would be at the west end of the house and I could drop it below the roof line and still have a reasonably clear shot at the 228T direction. Would putting it in the RF shadow behind the house, (and the house nest door), help block interfering reception from the other 2 directions? Just thinking out loud.
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Old 9-Jan-2015, 4:47 PM   #6
timgr
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My intuitive understanding of this is that the two antennas will create what amounts to an amplified multipath. I'd guess that you could move the two antennas around and change the degree to which that multipath is present. But that change might improve one station while others deteriorate.

I would try it if I had the materials on hand, and time to experiment some.
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Old 9-Jan-2015, 6:00 PM   #7
rickbb
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Time is the one thing I have plenty of, at least on nights and weekends anyway.

If the weather is not too bad this weekend I may try to hook up the other antenna at ground level just for the grins and giggles. I have everything on hand except for the reflector that still needs to be constructed.
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Old 12-Jan-2015, 7:28 PM   #8
rickbb
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Just got a reply from tinlee.com on a tuned combiner.

They said it was not cost effective to make one due to too many channels. 6 on one antenna and 40+ on the other.

I guess that's a good thing, having too many OTA channels.

Anyway, I'll have to be ready to play around with it this spring. It was too cold and windy this past weekend.
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Old 13-Jan-2015, 8:20 PM   #9
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Originally Posted by timgr View Post
My intuitive understanding of this is that the two antennas will create what amounts to an amplified multipath. I'd guess that you could move the two antennas around and change the degree to which that multipath is present. But that change might improve one station while others deteriorate.

I would try it if I had the materials on hand, and time to experiment some.
That sums it up pretty well.

One trick to try to add WUNC without causing multi path on the other stations would be to use vertical polarization on the WUNC antenna. WUNC just happens to be transmitting with both H and V pole signals.
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