Gidday Fellas.

I have been reading this thread with interest as I have a Magnum 257HP on it way to me down in Australia and I have picked up some good tips from here.

I have a electrical background but fairly new to RF type problems but learning fast. So notsoricer where is your antenna mounted and how low? I am thinking it is mounted on the rear door/spare carrier (forgive me if you have mentioned that)?

I am thinking that the defroster is acting as a antenna? I would reckon some of the more experienced HAM guys here will comment. Anyway have a good lads.

 

That never even occurred to me. And it's probably bang on!

In many vehicles, the AM/FM/SAT antenna is mixed in with the defroster wires (thinking sedans and the like here, not vehicles with exposed antennas like JKs). Even if there's no radio antenna mixed in with those wires, it's still a system which is seemingly designed to capture RF and let it get sucked in to the vehicle's wiring.

My JK doesn't have a glass rear window, so that never ever occurred to me. Nice catch!

If that's the culprit, and it seems quite likely to me if the antenna is mounted on the spare carrier, moving the antenna should fix the problem.

 

If the rear defroster was acting like an antena then more jeeps would have this problem arround RF sources. If resistance is the key So if your rear defroster is on, how do you think that grid warms up? Current flows into the ferris material causing the temprature to rise warming the glass. In this process the resistance rises as the temprature rises. Wouldn't this be like your chokes or beads and will cause the same effect on the circuit. .

I personally would seperate the bundles and make every effort to run the cable seperate from or perpendicular to ALL vehicle wiring. It's easier to do with bundles than individual wires. You just cross them at 90 degrees then crisscross 2 zipties at oposing diaganols lashing them together at 90 degrees. So no matter how the wires move, shift, or vibrate they are at 90's. Also, whe you have an area such as the door hinge where they will eventualy be parallel to cross that gap you may want to run shielding the length they are parallel. Make sure you Bond, Bond, Bond. The If you bond to the door, then bond the door and ensure there is continuity between the chassi and eventualy negative terminal to the battery. I've seen some vehicles need no bonding and others The door needed to be bonded to the chassis, which needed to be bonded to the engine, alternator, ECU, and battery. They key is common ground and a good free flow back to that ground. Wire burshing fasteners and cleaning out threads with a brass pipe cleaner goes along way too.

All else fails, run an antena external pillar mount and see where that takes you. It's a much shorter run of coax. But definately looks like you guys are collectively moving in the right direction. I'm curious to see how this turns out since I too am looking at a Cobra 75 based setup.