2 on the roof

[RossJ]

I want to add a mag-base GMRS 19" antenna on the roof of my dual cab (4-door) pickup. Right now I have a M/B CB antenna up there. How far apart do I need to put them, or is it not really workable? Thanks.

[De_Wildfire]

If I were to do it, I would make sure the GMRS antenna is at least 12-18 inches away from the CB antenna. This helps with potential signal interference or degradation, especially when transmitting at high power levels. The more separation the better but anything around a foot should suffice for most setups. I would put both antennas as vertically as possible and to have them aligned with the trucks roofline for maximum performance. I didn't have any problem with a K-40 CB antenna on the top left side of the trunk of the car, the two meter antenna in the top center trunk of the car and the 1.25 meter antenna on the right side top trunk of the trunk of the car. Nothing interfered with each other. GMRS is way up the bands that my setup and I don't think there would be a problem. When you keep dividing the GMRS frequency by two, four times, the harmonic ends up somewhere on the 10 meter band(28mhz)and that degrades four times. I hope this helps.

I stumbled on playing around with harmonics when I was a "kid" and came came across the FM radio frequency 104.5 by dividing by two all the way down the radio spectrum until was able to hear myself on 104.5. I set the old President HR-2510 to 26.125. I only needed to divide by two to use the harmonic to hear myself. Of course I did this on an old oil filled dummy load. This is for educational purposes only so don't try this at home.

[RossJ]

@De_Wildfire: I appreciate the response. Sounds like I should have enough room on top to place both antennas. I'll set them on the vehicle centerline and check SWR on each.... trial and error.

[De_Wildfire]

You are very welcome. It will be trial and error that's the fun part. Make sure you the doors are closed when checking and make sure you have a VHF/UHF SWR meter or an antenna analyzer that that covers up through UHF. Like with any mobile antenna after the placement, you may or may not need to adjust the whip. Just be real careful not to pinch the coax when making the run.

[RossJ]

Thanks again for the pointers. It's been nothing but spring rains here for the past several days... and some more to come. I've got to wait it all out before I start shuffling antennas around.

[De_Wildfire]

That's the same here with the rain. I'm playing around with putting a few VHF/UHF attic antennas up for the base station, but I want to get outside soon to put up a new dipole antenna for the low bands. I must say, the ground is soft enough to run coax and burry quickly. I think once this rain stops, I will have an antenna work party with a few 807's.

[Bozo]

Just try to put one toward the rear-center and the other up front or off to the side. The more distance you can give them, the better. And make sure both have a good ground plane — your metal roof is perfect for that.

Good luck and happy transmitting!