Connecting 2 different antennas on the same mast

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miguelaqui

miguelaqui

SatelliteGuys Pro
Original poster
Oct 14, 2004
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For years, I have had 2 antennas , one very large VHF and an XG 91 UHF only. I decided to point the VHF in one direction, where the one channel that I use comes from.
Wel, I was shocked to find out that, when pointed in different directions, the 2 antennas were inferring with each other.

Do I really have to have a low-mid VHF a full 10 feet apart from the UHF for them not to interfere with each other?
 
The passive element presence will always have an effect. The more distance, the less the effect. Are you using a combiner with separate VHF/UHF filtered inputs. If not, the 2nd antenna will be introducing phasing/timing issues (replicating multi-path).
 
Titanium said:
The passive element presence will always have an effect. The more distance, the less the effect. Are you using a combiner with separate VHF/UHF filtered inputs. If not, the 2nd antenna will be introducing phasing/timing issues (replicating multi-path).
Click to expand...
No, using UHF/VHF combiner SUVJ. I actually ran 2 separate cables, just in case I needed to use an A/B switch instead. I have them about 7 feet apart, but they still interfere with each other. I can rotate the UHF and watch the VHF channels go out.
 
I'd replace the U/V combiner as a test. (It's the easiest) I'm lazy/ therefore I try the easiest first)
If that don't work, I'd say you're in pretty strong signal area, Hope you're not using an amp. And placing the antennas apart may be necessary. (Separate masts) TVfool report?
 
I agree to replace the combiner
I have had my VHF and UHF about 4 feet apart at the lake house (they face different directions) and about a foot here in the cities and they both are fine. No issues
 
Iceberg said:
I agree to replace the combiner
I have had my VHF and UHF about 4 feet apart at the lake house (they face different directions) and about a foot here in the cities and they both are fine. No issues
Click to expand...
maybe I need to point out that I have a channel on 3, that is the channel that comes and goes, The TV Fool report says that 3 is strong, but it simply is not. The UHF interfere with the VHF, unless they are pointed in the same direction, west, or the uhf is south. I have run 2 different lines to make sure. I have disconnected the combiner just to make sure. The problem is that the VHF is simply not far enough apart. Maybe I need to just get a low vhf only antenna?
 
You sure your channel 3 is on RF frequency 3, my 3 is broadcast on RF 47. Low VHF channels are very rare.
 
rglore said:
You sure your channel 3 is on RF frequency 3, my 3 is broadcast on RF 47. Low VHF channels are very rare.
Click to expand...
Yes..It is on 3. Low VHF.. I have a 30db Antennacraft pre-amp as well. Just to show that TV Fool is not always correct...WGHP is a lot stronger than WRAL , WTVD, WYAT, WRDC or WLFL. Also, my 2 strongest channels are WXII and WUNL
Radar-All.png
 
miguelaqui said:
For years, I have had 2 antennas , one very large VHF and an XG 91 UHF only. I decided to point the VHF in one direction, where the one channel that I use comes from.
Wel, I was shocked to find out that, when pointed in different directions, the 2 antennas were inferring with each other.

Do I really have to have a low-mid VHF a full 10 feet apart from the UHF for them not to interfere with each other?
Click to expand...
 

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  • FILTER VHF UHF SYSTEM.pdf
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Take a look at the drawing that I put together for you.
Normally, if you feed separate UHF and VHF antennas into appropriate ports of a UHF-VHF combiner (Pico UVSJ or other equivalent), they will not interfere with each other. Unless the UHF signal is strong enough on the VHF antenna that it is providing a strong but out-of-phase signal that interferes with the other when combined by back feeding a 2 way splitter or even in extreme cases, a UHF-VHF combiner.

I created this idea about 25 years ago using terminators (Pico F59T) and three UHF-VHF combiners wired as shown. It makes a very effective filter network to keep all VHF out of the UHF side and vice versa. Much less insertion loss than a 2 way splitter, and band selective in all legs.
 
Do you notice this effect if you connect just the VHF down lead to the receiver (i.e. no possibility of out-of-phase signals from the UHF antenna mixing in the UVSJ)?

If so, then the proximity (and orientation) of the metal of the UHF antenna is reducing the gain of the VHF antenna.

The rule of thumb is that in order not to have this effect, two antennas must be separated by at least half a wavelength of the lowest frequency signal that is to be received. In your situation, that is about 8 feet.
 
From what I have read elsewhere like avs, WBRA is a bitch to keep stable due to interference. I'm sure Trip can comment on it as I know he has dealt with it previously.

But otherwise as noted above try and separate the antennas as far as you can. Usually that helps
 
Yes, WBRA is a pain in the neck. Every little thing bothers it. WBRA, due to its poor signal, was one of two things that got me into FTA satellite in the first place. (The other was Al Jazeera English, during the Arab Spring.)

I agree that the antennas should be as far apart as possible, but if they're close now and there is only have a problem when you reposition the UHF one, I would wonder if the UHF antenna is making WBRA's signal better or worse. That is to say, if you removed the UHF antenna from the mast entirely, would WBRA's signal go down or up?

- Trip
 
Iceberg said:
Thanks for the confirmation ;)
Click to expand...
I now have the VHF and UHS about 7 feet apart. There are 2 lines going up, so each attend has its own download. The VHF is stationary with the UHF being on the rotator. I can watch WBRA go out when the UHF is pointed in certain directions. Also, when I tested the VHF antenna, a few years ago before putting it up, placed on a table on my back deck, it was able to receive UHF channels as well, just not as strong, of course , as the UHF antenna. However now, even with them 7 feet apart, the VHF receives no UHF at all, with the exception of WWCW, which is so strong that it can be picked up with a rabbit ear inside my house. If they were still not interfering with each other, I should be able to get some signal from WSLS, WDBJ, WFXR, and maybe WPXR, which are all coming from the same location as WBRA.
 
I just wish that I has kept some of the negative traps that I came across while working in cable years ago ! Ih ad traps that took out all channels above 13, 2-6, cable channels 61 and up, I even had traps that would only pass FM! One system had a premium FM service that could be ordered by businesses on order to have music without commercials, a primitive version of XM I guess.

I found some on Ebay, maybe, I will use them to include another UHF in order to receive Raleigh all the time.
 
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