Dodge Charger VHF

[Andy Corbin]

My PD has a Dodge Charger that is about 2 years old. Configuration is a "slick top" with front headliner level LED's, TIR3's on the push bar in the front, back package shelf LED bar, and corner strobes in the front turn signals and rear taillight housings.

Radio equipment is a P25 800mhz system with a roof mount hockey puck and a VHF CM300 running 50 watts into a VHF 1/4 wave spike.

When we bought the car I was not consulted about the install or antenna placement. The "powers that be" wanted a very slick profile, so the installers used an NMO mount on the back package shelf metal framework (inside the car) and ran the whip up through the felt material with the whip bending to accommodate the rear window. The whip actually touched the glass near the top and increased in distance near the NMO mount on the package shelf behind the rear seat.

My concerns were RF feedback into the car electrical system via the rear window defroster grid. Also, there could be an issue of RF exposure to anyone in the back seat while transmitting on the VHF radio.
Thus far, there have been no problems. Perhaps my concerns were groundless.

I recently received a complaint from the officer who is assigned the car of short range on the VHF radio. I checked the radio and found 38 watts forward with 6 watts reflected on the antenna. After getting the necessary approval (not a big deal), I installed an NMO on the trunk deck, cut the existing coax, installed a mini-UHF female on it and spliced a male mini-UHF coming from the trunk lid NMO and installed the VHF whip outside. Performance and range MUCH improved as predicted with 49 watts forward, 1 watt reflected and a now happy police officer.

My question.

Your opinion- Were my concerns about RF feedback with the old antenna system valid? While ultimatelhy there were no problems, that would NOT have been the way I would have installed it.
and....were my concerns about RF exposure valid?

What say yee one....what say yee all.

Andy

[tvsjr]

My suggestion would be to read FCC OET Bulletin 65, which looks at RF exposure to humans. With a few simple calculators, for a unity gain antenna operating at 150MHz with 38 watts forward, and with the target 6 feet from the antenna, power density is about 0.38mW/cm^w, which is well above the 0.205mW/cm^2 allowed for uncontrolled areas. A prisoner in the back would be substantially worse.

I feel your concerns were valid, and I would not install an antenna in such a manner.