Cobra 29 ltd Shorted out?

[Jeep_Geek]

So here is the backround..
Was having trouble getting SWR at a safe level. So I started checking for shorts and opens in the antenna system. Found one right away. showed 1000ohms between the antenna and antenna mount, but only when the radios power plug is plugged in. have tried a different coax and antenna with the same results.
Test with radio power plug not plugged in

.
.
.
Test with the radio power plug plugged in

.
So I did a little test in the house on it as follows:
In the vehicle the radio and antenna share the same ground/counterpoise so thats the reasoning behind the jumper between the - power for the radio and the shield on the coax. (I think)

It shows the same 1000ohms as while in the vehicle...
I have opened up the radio and cant see any signs of burnt or melted components.
So is my radio messed up ?? or is this normal??

 

[loosecannon]

while i realize that you are placing a lot of importance on that 1000ohms reading from the radio, and it may well be an issue of some sort, lets start with the basics to make sure we dont miss anything.

the simplest solution would be to substitute a different known good radio for your radio in the vehicle and see if the SWR is lower.

my initial guess is that it wont be.

from your diagrams im assuming that this is the type of mount you are using.

what antenna are you using? has it been cut or modified in any way?

where is the antenna mounted on the vehicle?

the details you provide here will allow us to localize the problem to either the radio itself or the antenna installation. (much more likely)

oh, what radio is it, and has it been modified in any way?
where is it powered from in the vehicle? where is the ground wire for the radio attached to the vehicle?
LC

 

[Jeep_Geek]

Its a Cobra 29 NW Ltd classic ( used ) opened up looks like someone cut JP36 and put resistors on opposite side to lower the deadkey
I had first thought I had a counterpoise problem (not enough)
It is in a 92 Jeep Wrangler
My antenna is mounted on the passenger side front fender on a stainless mount with paint ground off under the mount. I also ran a 4awg grounding strap from the mount to the firewall grounding stud for the vehicle and then one to the frame. I would think its grounded good enough but
The two antennas I have tried are a 3' firestick 2 with tunable tip and a K40 bottom load with steel whip.
I will hopefully be able to test it with a friends cb later this week.
Any other thoughts??
Thanks

 

[loosecannon]

well there ya go.

you have combined a bad antenna mounting location with bad antennas.

that is why your SWR is high. your radio is probably fine, unless you have been transmitting with it over and over again into this high SWR.
it takes a lot to blow a radio's final transistor from a high SWR, but it does happen.

first of all, stay away from any CB antenna that is less than 5 feet long.
firestik antennas are crap antennas that are peddled to the 4-wheeler guys because they dont know any better.

an antenna needs counterpoise. that means a horizontal flat metal surface directly under the base of the antenna. a ground strap, no matter how much paint you scrape off, does not create this.

there is a HUGE difference between DC ground and RF ground, which is what we are dealing with when discussing antenna counterpoise.

remember that only the portion of your antenna that sticks up past the top of the vehicle is actually radiating a signal. the rest is radiating directly into the metal body of the vehicle.
signals exit an antenna out the sides, not out the top.

add all this up and you can see why your SWR is high.

i know a few guys into the off roading scene, and a few guys into the "truck club" scene.

they all want to run CB's in their trucks, but WILL NOT mount a big honkin' antenna on them.

once they find out that they have to have a big antenna that looks obnoxious (beautiful to some LOL) to get any sort of performance out of a CB radio, they drop the idea.

do some searches on this forum regarding mobile antenna setups and things like that.
you will learn a lot about what does and does not work well.
LC