Batboard

While checking a suspected antenna problem on my truck radio, I ran across something that I've never seen before. I don't have a watt meter available right now so I was checking for a direct ground on the coax with a volt/ohm meter and did find continuity from the shield to the center cable on the coax. When I removed the cable from the radio, the continuity was gone. I checked the radio's coax connector and found continuity from the center to the ground on the radio itself. Just to verify my concern, I checked two other radios the same way and one had the ground and one didn't. The other radios that I checked are in vehicles and have no problems that I am aware of. Please pardon my ignorance, but I was always taught that there should be no continuity from the center wire to ground. Am I wrong or do I have a problem with the radio?

Thanks

Bundy125

depends on the radio
The short may be a short at 0 hz but at 400 MHz it may be open.
It is probably an LC circuit of some kind for matchinhg.
Now if all the radios are identical there is a problem but it may be meant to be a short. and the opens may be faulty

Thanks fo the reply, that makes me feel musch better. I've just realized that I posted this in the wrong forum. Sorry about that mods

Bundy125

I would suspect that the great majority of radios show a DC low value at the antenna port--normally

Most radios designed for mobile applications have an inductor directly from antenna circuit to ground to drain off the static charge that builds up, especially in dry winter weather, as your antenna whips through the air at the speed of your vehicle. If undrained, this charge can easily build up to 5-10kv, potentially damaging the output circuitry of the radio.

Many what we call RF "tank circuits" will show zero ohms
which they are at DC but they're not when the RF is running.
This confused the hell out of me the first time I ran into it as well.
Same thing for antennas unless they're a simple quarter wave.
It's a pain in the neck to check the coax but to do so if the
antenna has a coil in it you have to disconnect the cable
from both the radio and the antenna.

Hi All,

Many thanks for the replys. Y'all have eased my mind a great deal. I was kinda worried that I'd be needing to send it out for repairs, but y'all have (once again) came through.

Bundy125