CB antenna behind GMRS antenna (radiation pattern affects?)

[GrouserPad]

I've always preferred to run my antennas center of the cab to give me the most omni-directional signal as possible. I have a pickup truck and was thinking of running my gmrs magmount 5/8over5/8 antenna infront of a base loaded wilson 2000 cb antenna. There would be about 1.5ft between the antennas loading coils. Does anyone know if this setup will cause one of the antennas to become a reflector of the other and make me extremely directional? What other effects might this cause if any? I'm more concerned about their proximity to one another negatively influencing my gmrs range, as gmrs is what I use to do coms with my home base often. And unfortunately it seems I'm always on the fringes of gmrs service so I'm pretty concerned about the negative effects if there is some.  CB is only for interstate road trips and takes a backseat to my gmrs all other times.  If this is more in-depth than gmrs ever was ment to be I apologize and you can leave this thread to die in the weeds of the forum. I know I tend to get a bit obsessive about details. I apologize.

[WRYZ926]

You normally want the antennas to be at least a 1/4 wave length apart which is not going to happen with the CB antenna as you would need 8 1/2 feet. My brother runs a Comet 2x4SR multi band VHF/UHF antenna on the top of his truck cab with a Tarheel HF antenna mounted to the left front corner of the truck bed. Has has at least 3 foot of separation between the antennas and he has no issues.

You might find that the CB antenna does act as a reflector for the GMRS antenna being 1 1/2 foot away which can cause the GMRS antenna to be more directional. The only way to know for sure is to try it out. You should not have any interaction when it comes to transmitting since we are talking about 11m vs UHF. 

[Socalgmrs]

Nope. No issues at all.  Totally different frequency range.  Plus the gmrs uses ground plane and the cb does not. 

[GrouserPad]

5 minutes ago, Socalgmrs said:

Nope. No issues at all.  Totally different frequency range.  Plus the gmrs uses ground plane and the cb does not. 

CB absolutely does require grounplane and its radiation pattern is affected by it as well. But I was curious how the two difffering frequencies would see eachother mounted that close...... be cool if I could run both like that with no ill effects. I figure I'll have to do some real world testing.  

[WRTC928]

I have both on the roof of my truck and I haven't noticed any change in directionality. Since the two operate on such widely different frequency ranges, it's likely the CB antenna is no more than any other piece of wire to a GMRS signal. As such, it could affect directionality a bit, but I haven't noticed it.

[WRYZ926]

Normally one would put a second vertical antenna up that is a 1/4 wave length away from the main radiating antenna to get some gain and directional characteristics. A 1/4 wave for GMRS is only 6 inches. So that chances of that happening are definitely less with the antennas spaced at 1 1/2 feet apart. Yes there is still a chance of making the GMRS a bit more directional but not like if the CB antenna was only 6 inches away from the GMRS antenna.

 

[OldJunk2]

My CB antenna is 8" from my GMRS and I have zero issues with either radio