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shadow

Member
Aug 4, 2009
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hi all, have had a lot of rf interference from my mobile cb, ive tried ferrite blocks, capacitors, and wrapping 20' of cable round a shackle with a capacitor, all to no avail. now tonight ive noticed while im getting the interference noise, if i touch the cable or the outer casing of the mic, it stops, could this be a fault in the mic, its almost like im an earth for it. the mic is approx 8 years old.
any help would be grateful
 

Hi Shadow, I have had the problem before and it has usually been a weak connection of the ground or shield wire on one end of the cable or the other. I have found it is usually found in the mic plug end as it gets the most twisting and pulling. It would be worth a check. Hope it helps.

skipper1
 
sounds like you have a grounding problem.

i know you've posted it before, but would you mind giving us a quick rundown of your setup?

how is the cb mounted? to what?
where are the power and ground wires run to?
what model of vehicle is it?
what is the antenna mounted to?
anything else in line?

thanks,
LC
 
cb is mounted on side of centre console, screwed into the plastic, the power is direct from the battery, throught the bulk head of the car, i have a magmount 1.5 m whip aerial, i have the ignition noise suppressor inline on the power lead, and the car is a vauxhall vectra, if you know what that is, its a uk car, also same as the opel vectra b, just seemed wierd that when i moved the lead of held the mic the noise stopped, and it is old
 
just guessing, but maybe the negative leads going from the battery to the chassis and the engine block need to be replaced.

get a nice new battery terminal and two battery leads of at least 4ga. wire; whatever length you need for your car, and attach one lead from the battery's negative terminal to the vehicle's chassis.
attach the other lead from the battery's negative terminal to the engine block.

unless your car is very rusty and you cant trust the ground connections from body panel to body panel; it would be better to keep the negative wire from your CB to under a foot long.
just ground it to the nearest bare metal that is attached to the chassis of the vehicle.

again, im just guessing here, but seeing as you live in a very humid climate; the possibility of your grounds being corroded or otherwise deteriorated is high.

who knows, the new ground wires from the battery to the chassis and the engine block might just solve all the problems you've been having.
this is what i would try first.
even if it doesnt fix it; you have still improved your vehicle!

good luck,
LC
 
Do you know anyone who has the same radio, or a mic that will work with your radio? I think I would try that before replacing a lot of wiring. Or try your mic on someone else's radio? Before chnging all that wiring, I think I'd also try grounding/earthing the radio's case closer to where it's mounted. Doesn't have to be 'permanent', just to see what happens.
- 'Doc
 
doc,

you have to take into account his other posts.
this is not the only problem he is having.

also, remember that with a CB radio; the chassis is isolated from the negative power lead.
i know in ham radios, the case is ground, but not in a cb.
well, 99% of cb's anyway. the cobra 19plus is grounded to the chassis.

im not saying that your idea wont work, but knowing about the other issues he's having; the vehicle's ground connections seem like a good place to start.

and hey, we're only talking about two wires here.
certainly wont hurt the vehicle to upgrade the ground wires.
LC
 
gd posts by both, thanks for the input, im gonna be doing a lot of work to the car soon, so il try both suggestion, keeping the earth short makes sense, same as the amps i have in the boot, and the new earths wont hurt in the engine by at all, its 13 years old after all. cheers guys
 
shadow,

if you've got any kind of an amplified stereo system in the car, then upgrading the ground wires will be a big help there too.
the other one to do is the wire going from the alternator to the positive terminal of the battery.
should be at least 4 gauge and factory is usually 8 or 10 gauge.

in car audio they call this "the big three" upgrade.
YouTube - Rockford Fosgate RTTi- How to upgrade the big 3

check out that link for more info on it.

good luck,
LC
 
ground the radio somewhere off one of the mounting bolts or a case screw.
try another mic first is the easiest way .if it does it with another mic try grounding the radio.
check to see if the ground/shield wire inside the mic is loose.if all else fails ,try a skythumper mic .i havent seen a radio yet that mic would not tame
 
ok, earths are now shotened, i ran an earth lead from the cb mounts, this helped a lot, ive also taken the mic apart, there was one connection with no solder, so sorted that, and on the plug end, one of the cables had no plastic shielding and had obv been touching the metal plug, so ive insulated that, il test it tomorrow. thanks for your help everyone
 

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