Batboard

I recently had my 15 or so year old analog 110w VHF Spectra A7 replaced by a used 110w VHF Astro Spectra W3. A week earlier I had a Whelen Cencom siren/light controller installed. Cables for the Cencom (control head to trunk amp, where 12v and all accessories are connected) were run down the right side of the vehicle and the siren amp was mounted verically to a support post on the inside wall of the right rear fender. That installation was performed professionally by a company that has installed hundreds in a similar manner.

My local Motorola shop did the A7 removal and W3 install. While I mentioned to the installer (also very experienced) that the new Cencom wiring ran down the right side and that he should avoid it wherever possible, since the A7 cable was removed from the right side he laid the W3 cable there as well.

After the install, however, I noticed that when I keyed my VHF mic on certain VHF frequencies (apparently any repeater input freq in the 158-159 range), the RF activated my dual talon (behind mirror) and front LED grille lights. For some reason this did not occur when transmitting in the 154-155MHz range on a simplex channel.

The antenna system on the 2003 CVPI is a Sti-Co dual band (150-450) trunk lip mount disguise cellular lookalike. This has not changed from the 110w VHF Spectra A7 that was removed. I also noted that one of the two trunk grounding straps (trunk lid to metal trunk mechanism) was seperated.

Coincidentally (perhaps), I was not getting optimum VHF reception on the Spectra A7, leading me to connect a VHF mag mount antenna to it in recent months. During this install, however, the installer/technician used an SWR meter to verify that the newly installed VHF A3, operating thru the Sti-Co dual band antenna described, was putting 100w out with less than 5 watts reflected.

The car is going back to the install shop on Monday. Has anyone had a similar RF problem with a Whelen Cencom cable sharing a cable run with an Astro Spectra? Any other RF issue suggestions? Could there be problems in the Astro Spectra W3 transceiver itself (I do have another one at my disposal)? Should I consider replacing the trunk mount Sti-Co? Any thoughts/help is appreciated.

Id first check the grounds on the Sti-co. If its a trunk lip mount all that is grounding it is the 2 allen screws. Take those out and clean them up scuff the place where it attaches to the trunk to bare metal. Also does your CV have the braided ground straps on the trunk hinges. Ive seen a few that don't. Do the Cencom and the Spectra share a common ground or power? How close is the trunk unit to the cencom? Also how close is the talon to the antenna? Sounds like there is RF bleeding allover and somehow getting into the cencom.

Just a few suggestions to look til you get it to the shop

It's a CVPI. Why even bother with 'disguise antennas'. You have the strobes. It already looks like a police car.

Earth to poster: you're not fooling anyone.

The reason I prefer/use Sti-Co disguise cellular look alike antennas is because they make a dual band (VHF 150-174/UHF 450-512) broadband (+/- 24 MHz on VHF & greater on UHF) reprotedly capable of handling up to 150 watts. I've heard of a few other (Antennex, Maxrad) dual band models, but none that I know of will handle the 151-162 or 453-483 range that I need and none have a 24 MHz split. I like using one antenna for my main VHF and UHF radio. I also have a digital scanner connectied to a quarter wave antenna. Crown Vic or not, I prefer ont to have 3 antennas on the trunk.

nylawman wrote:The reason I prefer/use Sti-Co disguise cellular look alike antennas is because they make a dual band (VHF 150-174/UHF 450-512) broadband (+/- 24 MHz on VHF & greater on UHF) reprotedly capable of handling up to 150 watts. I've heard of a few other (Antennex, Maxrad) dual band models, but none that I know of will handle the 151-162 or 453-483 range that I need and none have a 24 MHz split. I like using one antenna for my main VHF and UHF radio. I also have a digital scanner connectied to a quarter wave antenna. Crown Vic or not, I prefer ont to have 3 antennas on the trunk.

Understood. I know how you feel. I have melted lesser antennas. =)

After reading the previous posts, there are some other things to consider if those didn't work. This comes from much NCSHP CV installation experience involving high power radios and Cencoms.

The lack of a good ground on the antenna and enough SWR (mismatch) can allow any reflected RF to become radiated to adjacent wiring in the vehicle. The more RF reflected, the more induced problems you'll see. Once you get a good ground on the antenna mount and trunk lid, you'll probably find you'll have to re-tune the antenna(s).

Ideally, cables carrying RF or sufficient EMF should never run parallel with each other so that one can't induce EMF/RF on the other. Kinda hard to have all cables crossing each other in any kind of installation, so you have to resort to other methods of killing the effects.

Is the shield on the Cencom control cable grounded on both ends? If not, ground it. This usually stops the problems if the antennas and feedlines are done right, but it should be done anyway.

Is the Cencom wiring anywhere near or parallel to the antenna feedline(s)? If so, move 'em so they aren't close or parallel to any other cables or wiring anymore than they have to be.

Are there nice neat coils of the excess Cencom control wiring lengths? If so, they're acting as induction coils. Flatten the coils and tie/tape them as flat as possible so that they don't get the chance to act like inductors. This applies to any excess wiring lengths you don't want/need to cut, including the excess radio cabling and wiring and the warning lighting wiring.

The Cencom unshielded wiring lengths should be twisted as though making a cable assembly so that the individual wires have little chance of being parallel to anything except each other, and any excess lengths should be coiled and flattened and secured.

There are some other things you can do also, but this oughta get you started.

Silly question: do you have a good RF bond from the trunk lid to the frame? I couldn't get my Tarheel to tune worth a darn on my Grand Marquis until I ran a bond wire from the trunk lid to the frame.

Now, if I could just get the eight coil-on-plug ignition modules to be quieter on HF....

Wowbagger wrote:Now, if I could just get the eight coil-on-plug ignition modules to be quieter on HF....

Not as bad the Dodge ignition system on the 5.7L V8...noisy as all get out.