Instrument Lamps come on when radio is keyed

[Fire232]

I installed a CDM1250 in a Canyon with a hood mount antenna and when the radio was keyed to transmit the intrument panel lamps came on, mainly the ABS light. Has anyone heard of this before and can tell me how to avoid this? Currently it was switched out with a glass mount that we are unable to tone and have heard nothing but bad things about these.

[Tom in D.C.]

You'll have to relocate the antenna; the RF is obviously getting into the
vehicle's computer and/or switching circuit. Your antenna is probably sitting
somewhere above the ABS system under the hood. I had a Pontiac once that whenever
I keyed the transmitter in motion the cruise control would drop out. It's one of
those things that varies from car to car, antenna location, amount of RF power, etc.

About glass antennas, don't be too quick to dismiss them. Most people who complain
about them might not understand how they work, how to install them, and how to tune
them. I've probably run six of them over the years and on every one I was able to
get the SWR (the matching of the antenna to the transmitter) to a near-perfect level.
One of the things overlooked is that if you have a frequency resonant feedline you'll
never get a good match, so if all else fails cut the line by a foot or two and put on a new
connector and that should clear things up.

[Bat2way]

One of the things overlooked is that if you have a frequency resonant feedline you'll
never get a good match, so if all else fails cut the line by a foot or two and put on a new
connector and that should clear things up.

I've seen where the coax had been cut short in a previous install for some reason and when reinstalled in another vehicle later, caused this problem.

[DAC]

#1
It may be a poor ground in your instrument panel itself, try removing the radio or control head from the under dash mounting, if you have it dash mounted, then test it again, if the light doesn't light you have found your problem.
#2
try a few snap on ferrite beads available at many ham amateur radio online and some local shops. http://www.dxengineering.com/Products.a ... &DeptID=32 has then but rather high priced, make sure you get them for the correct diameter of your coax. They are available at many places, do a "ferrite bead" search at Google. If these don't cure your problem you will still have them for future use, they should be in the inventory of every good radioman. They can be used on base as well as mobile radios and on power cables for 12vdc, 110vac and on coax, if your TV has RFI they can be used on the TV, DVD, VCR, ETC. power input and coax as well, they are very useful and are a cheap cure all.

[n3lee]

This is caused by RF getting into either the ABS unit or the PCM; neither situation is good.

If you've absolutely got to have the antenna on the fender for whatever reason, you may want to look into changing the actual RF cable out with something with a quad-shield; some of the NMO mounts use standard RG-58 and it is very lossy -- meaning that everything NEAR the cables get flooded with RF. The other thing you can do to mitigate interference is to re-route the cabling -- keeping it away from the main wiring bundles wherever possible.

Another thing that is possible-- if there isn't a good DC ground on your antenna connection, sometimes the ground-plane will "extend" its self onto through the coax, and through the vehicular wiring to the DC ground -- this also causes an unbalanced effect on the positive terminal -- allowing RF into your DC electrical system, which can cause problems.

The easiest way to tell if you can fix things by moving the antenna is to borrow an NMO magnet mount with the mini-uhf antenna and move it around the vehicle -- i often do this on new-model vehicles and route the coax near its final destination to determine if there will be an electrical / RF issue. it also pays to take the car for a short drive around the block while transmitting / testing if possible -- this ensures that all the sensors are working properly (wheel speed sensors, VSS, etc)

Good luck!

de N3LEE

[TheZach]

The county has an emergency management truck that used to turn on the the red/blue grill lights when the radio is keyed up, I can't remember what they did to solve it.

[HLA]

i've seen a uhf ht1250 trip a gfci breaker when it was keyed up so it may be activating a relay too? what band or frequencies is this radio on?