Antenna Interference

[SpugEddy]

So, from the pictures, the problem is now obvious. My question is:
Will the solution be as simple as a 14' relocation.

The antenna on the left is an A99 10-11 meter antenna.
The antenna on the right is my Ed Fong for GMRS

Each antenna is causing interference with the other. I had the Ed Fong
just leaning against the shed on a pc. of mast with RG-59. I moved it
to where it is in the picture and changed the cable to LMR-400. My SWR
got worse! If I move the Ed Fong to the front of the shed then they will
be separated by 14'. Will this fix my interference problem? And, will it possibly
lower my SWR below 2:1?

 

[mmckenna]

Likely.
Having two antennas too close to each other can cause signal to be reflected which will show as a high SWR. That is PROBABLY your issue.

There can be other things that will cause high SWR that won't be resolved by moving the antenna.

Also, having two antennas that close together can overload the front end of the radio in receive mode while the other one is transmitting. If the coupling is good enough, you can get enough RF energy into the front end to damage it.

 

[SpugEddy]

I immediately thought of moving the antenna to the front of the shed
but I'm apprehensive about drilling more holes into the siding only to
be wrong. If I feel confident that moving it will do the trick then no loss.
As for the overload, that's why I never have both radios on at the same time anymore.
When i have both radios on, the 10 meter radio receives interference when one of
the GMRS repeaters ID with their code.
I really thought the 2 antennas would live together in harmony since the bands are
so far apart. (26 mhz to 465 mhz) but no such luck I guess.

I'm even starting to wonder if I ultimately built a huge "J-Pole" antenna.
Here is what I have out back:
Unistrut at the top and bottom of the shed mounted on the wall.
Antenna 1's mast mounted to the unistrut with 1 1/4" clamps
Antenna 2's mast mounted the same exact way.
Antenna 1 is the 10-11 meter A99 and the coax RG-8 comes
into the shed in the front
Antenna 2 has LMR-400 coming in through the rear of the shed.

 

[prcguy]

At GMRS freqs a half wavelength is 1ft and you look to be further away than that so you are probably just fine. The CB antenna should not even know the UHF J pole even exists due to its small fraction of a wavelength at 27MHz. You should be able to bend the two antennas apart a bit while watching the match and that will tell you if the close proximity is the problem, which its probably not.
prcguy

 

[mmckenna]

As for the overload, that's why I never have both radios on at the same time anymore.
When i have both radios on, the 10 meter radio receives interference when one of
the GMRS repeaters ID with their code.

Shutting the power off does nothing to disconnect the antenna from the receiver. It won't protect anything.

Not sure I agree with PRC, but it won't hurt to move them apart. Having them that close together isn't doing you any favors.

Unistrut will work fine. I've mounted small antenna with it. The conduit/pipe clamps are not really designed for that sort of load (pushing down through the clamp). You might need to fabricate some sort of stop to keep the support pipe from sliding down. Or not....

 

[SpugEddy]

Unistrut will work fine. I've mounted small antenna with it. The conduit/pipe clamps are not really designed for that sort of load (pushing down through the clamp). You might need to fabricate some sort of stop to keep the support pipe from sliding down. Or not....

Agreed. After the last storm, I'm working on a U-clamp bracket with some all-thread idea. The actual 1 /1/4" mast is about 2'
off the ground and then fitted into a piece of PVC with (4) 5/16" bolts securing the mast to the PVC. This keeps the weight of the
whole structure directed right into the ground. The PVC is to prevent the mast from rusting at the ground level.

 

[mmckenna]

That would work. Uni-strut is useful stuff and you can increase it's usefulness with a bit of light fabrication.

I have mounted a few antennas with it. I had a 3dB UHF antenna mounted on the side of my house with a piece of uni-strut, back when I was active on GMRS.
I've got another 1 1/2" short mast mounted on one of the roof tops at work for testing and temporary setups.

And to clarify my above statement. I agree with what PRC is saying, but I'm not sure there's a foot between those antennas. Moving them apart will help your situation. If you are going to move them, might as well move it to the other end of the building. Again, more separation isn't going to hurt. If cable length isn't an issue, then I'd go for it.