Multiple Mobile Antennas

[KB9YZL]

I currently work for the Meteorology Department of the local Community College as their "Radio Guy". (A position I fell into, due to my knowing just enough about radio gear to be a danger to myself.)

Over the past ten years, our mobile electronics have gone from a single CB, to the 11 antenna setup currently being worn by our lead van.  This setup includes two 2M sets, two CBs, three scanners, one TV, one GPS, and two cell phone antennas.  Aside from looking like a porcupine, everything seems to be functional, but I am concerned about interaction between the various sticks up there.

I have noticed significant changes in SWR when an antenna is evaluated individually, and then checked again as part of the whole setup.  It's not bad enough to keep me from keying up, but it's troubling to see an antenna go from 1.2:1 when measured alone, to 1.7:1 when it's part of the group.

I am not an electronics wizard, (obvious, isn't it?) so I'd like to hear some other opinions on the subject.  Thanks in advance!

Kent
KB9YZL

[K5LXP]

First off, the SWR differences you're seeing aren't significant enough to worry about.  You *could* optimize each one for *absolute* performance in the environment it's installed in, but I doubt you'd see a measurable difference when you're done.  I've got 8 antennas on my truck, I find the interaction minimal.  Surely I overload the front end on some radios while transmitting on one band or another, but receiving on other bands while transmitting isn't a requirement in my case.  If you want to improve the isolation between some radios, look into getting a combination of diplexers and triplexers, available from the likes of Comet and Diamond.  The port-to-port isolation on these is pretty good, and might give you antenna/radio options you haven't thought of yet.

Mark K5LXP
Albuquerque, NM
k5lxp@arrl.net