Hey all.
I've got a question about a recent cb adio install on a 2000 dII.
I installed a Cobra 75wx st with a 4 foot Wilson Superflex antenna and 18 foot coax cable. The cable is not coiled and I used soldered on connectors. The cable is run under the load space carpet on the passenger side, under the rear seat carpet then under the front seats themselves.
It seems that I get noise when the engine is running.
It's not speed sensitive and doesn't sound like the typical dirty power whine.
I have the power coming directly off the battery with the ground point about a foot from the unit.
I put in a power filter with no effect.
The swr is at 1.5 on channels 1, 20 and 40 so it seems pretty ballanced. I can get rid of the noise with the sq setting but lose a lot of signal that way.
The antenna is on the spare tire mount with about 2 feet above the roof line.
Anyone have any ideas? Thanks, Walter

What kind of noise are you getting, is it a pulsating noise or a whining sound or something else?

Does it really only appear when the motor is running, or does it start when the ignition is switched on?

It might be that the cable runs close to an electrical motor like a fuel pump or something.

It's not a pulsating or whine type sound. More like a high pitched squeal.
Good point about running or ignition on, I'll check that.

Disco's are very noisey (noisy?), radio wise. All the computer controllers have a##loads of spurs and harmonics and sidebands. I've listened to it from 1 to 50 MHz and it sucks over the whole spectrum. You'll hear them talking as soon as the ignition gets switched on. The fuel pump is loud but not the worst offender by a long shot. If your noise increases a lot when the engine starts thats probably fix-able.

If not, ground the radio and the antenna as well as you can and forget about it - it's not getting fixed without major retrofit.

keith "why, yes, I am a radio engineer, thanks for asking..."
:usa:

I checked and the noise comes on when the engines running and not with the ignition.
I think I'm getting it over the antenna. I'll ground the antenna and re-checkmy swr this weekend. In the meantime if anybody's got any more ideas, let me know.

Hey my friend had the same problem, so he grabed power from the stock radio instead of running a wire to the battery. I think they put in some real good filtering for the radio power. Before he did this he could not even here another CB unless it was less then 15 feet away.

Mike AKA Electromagnetic Tech.

Your SWR will have litle to no impact on the received signal/noise ratio. In fact, I'd question your flat SWR over the entire frequency range as that is indicative of a very inefficient antenna, or poor instalation.

Disconnect the antenna while the engine is running to determine if the noise is coming through the antenna or the power leads. Coil the antenna line near the antenna in a coil the diameter of a coffee can (not too tight). Ground everything.
Ignore what you've heard about magic lengths of cable.

Thanks for the input guys. According to the literature that came with the antenna, the ground wire that is on it is for reducing the swr if you can't get it with the provided adjustments, so If I use it I will likely have to adjust it again.
Good point about unhooking the antenna, as an electrical technician I should have thought of that. Duh!

According to the literature that came with the antenna, the ground wire that is on it is for reducing the swr if you can't get it with the provided adjustments, so If I use it I will likely have to adjust it again.
Good point about unhooking the antenna, as an electrical technician I should have thought of that. Duh!

Regardless of what it may say, a good RF ground at both the antenna and the rig is absolutely critical for efficient operation of this radio. At 11 meters, and AM, with only five wattsof input power, you need all the help you can get.

If Keith has put a spectrum analyzer on his rig and it's dirty through 50 Megs, you may always have some noise that you can't screen out, unless you have the time and energy to bypass each and every noise source.

It sounds like you are having noise on the incoming -- mine puts out noise on the outgoing.

Any suggestions? I am runnig a Uniden XL Pro 5xx with a 4' fibreglass whip with a spring, solid mounted to the tail gate of my Xploder.

It sounds like you are having noise on the incoming -- mine puts out noise on the outgoing.

Any suggestions? I am runnig a Uniden XL Pro 5xx with a 4' fibreglass whip with a spring, solid mounted to the tail gate of my Xploder. SWR is under 1.6 on both ends, and sound coming in is clean as a whistle - but everyone hearing me says they can't understand a word I say -- lots of distortion and feedback type sounds coming out of their speakers (in multiple other trucks).

Thanks

It sounds like you are having noise on the incoming -- mine puts out noise on the outgoing.

Any suggestions? I am runnig a Uniden XL Pro 5xx with a 4' fibreglass whip with a spring, solid mounted to the tail gate of my Xploder. SWR is under 1.6 on both ends, and sound coming in is clean as a whistle - but everyone hearing me says they can't understand a word I say -- lots of distortion and feedback type sounds coming out of their speakers (in multiple other trucks).

Thanks

Several possibilities.

1) Check antenna match with somebody elses meter. Cheap meters = cheap results. Bad (even a little) antenna match really raises hell with modern CB radios.

2) Bad ground on radio. Best ground is right to the NEG on the battery.

3) Bad mic on your radio - for some reason this happens all the time.

4) Check the DC voltage right at the radio when you transmit. If it drops below vehicle voltage AT ALL, rewire the B+ (hot) to the radio.

5) Does your radio have a "transmit clarifier" or some other bogus way of shiftig your transmit frequency ? Maybe you're off frequency.

6) Have the other guys turn down thier volume while listening to you. Does it sound better then ?

keith
:usa:

Roverhound - I had noise on my CB when I had the cable laying across the loadspace of my RRC. I think it came from the fuel pump and I cured most of it when I rerouted the whole cable outside of the body along the frame.

1) Check antenna match with somebody elses meter. Cheap meters = cheap results. Bad (even a little) antenna match really raises hell with modern CB radios.

I did this when I did the antenna install and the SWR was good.

2) Bad ground on radio. Best ground is right to the NEG on the battery.

This bears further checking. I grounded the radio through the console in the truck, and just figured that a ground was a ground.

3) Bad mic on your radio - for some reason this happens all the time.

This was my initial thought, so I purchased a new Cobra mic, it did the same thing.

4) Check the DC voltage right at the radio when you transmit. If it drops below vehicle voltage AT ALL, rewire the B+ (hot) to the radio.

This I haven't done, but my wire comes directly from the fuse panel to the console for the radio with nothing else hooked to the circut. I will check it.

5) Does your radio have a "transmit clarifier" or some other bogus way of shiftig your transmit frequency ? Maybe you're off frequency.

Nope. Just a plain Jane radio. No special mic controls or other broadcast controls. I am possibly off frequency however, (that is what it sounds like) I may have the radio peaked and tuned.

6) Have the other guys turn down thier volume while listening to you. Does it sound better then ?

That has not mattered, and it is across a spectrum of other radios (as in EVERYONE says my radio sucks...)

As a side note, I pulled this radio out of another vehicle that had similar issues. That antenna was shot, so I thought that was the problem, but evidently not. Thanks for your suggestions...

As a side note, I pulled this radio out of another vehicle that had similar issues. That antenna was shot, so I thought that was the problem, but evidently not. Thanks for your suggestions...

Well, if it's not the ground, it sounds like the radio is shot - sorry.

SOMETIME'S ground is ground, but not always. On high power gear that draws respectful amps, pulling ground back to the battery works best. On low power gear like CB, try to utilize any place the OEM grounds to - then you're pretty sure it's a decent ground.

keith
:usa:

Yeah,
I'm leaning towards the radio being junk... I used if for a lot of years when I drove big rig on the road and it has taken some abuse in the off-road truck now.

I'll start shopping for another one.