Static over CB as soon as start engine

Submitted: Saturday, Apr 04, 2009 at 17:51
ThreadID: 67530 Views:2587 Replies:7 FollowUps:1
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Hi all,

I have a Uniden UH090 CB radio in my Patrol. This model covers both the old AM band (27 Meg) and the FM band (UHF).

I always thought the AM side of it wasn't working so just used it on UHF.
Today I got an opportunity to test it with someone who only had an old AM radio. We were parked at the time. I was surprised when it seemed to work perfectly.

The problem is that as soon as I started the engine to move off back came the constant "scream" of static from the radio. Not bearable and you wouldn't have heard any behind it.

Does anyone have any clues as to what might be causing the problem? Hopefully there is a simple fix such as a suppressor required or something. I may as well have it usable if it is not a major problem.

I do have the 2 separate antenna required by the way.

Thanks for your help

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Reply By: Member - Doug T (NT) - Saturday, Apr 04, 2009 at 18:34

Saturday, Apr 04, 2009 at 18:34
It's normal.... HF 27mhz is very prone to interferance, You can even hear a charge of lightning building up during a storm .

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AnswerID: 358049

Reply By: Ozhumvee - Saturday, Apr 04, 2009 at 18:55

Saturday, Apr 04, 2009 at 18:55
We just used to turn the squelch up until background noise was muted, at that point good strong signals would still be received but all the hash and background from weak signals would be removed.
Basically the squelch knob reduced the sensitivity of the receiver.
You can do the same on most UHF's too.
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AnswerID: 358054

Reply By: obee1212 - Saturday, Apr 04, 2009 at 20:04

Saturday, Apr 04, 2009 at 20:04
make sure the earth side of the antenna (braid) is making good contact with the chassis. (And the centre wire with the antenna.

move the antenna to somewhere away from the engine bay.

The interference will be coming from either the spark system or the alternator.

My amatuer radio years ago used to pick up noise from the alternator the motor being diesal. I moved it to the back corner of the ute to overcome it.

hf will pick up a lot of stuff that the uhf won't.

clip a wire onto the braid and take it to the negative side of the battery and see if it makes a difference.

The antenna needs to be cut to the hf band. Might need to change antenna if you want to use hf (27meg). An antenna cut for uhf is unlikey to work with hf. An antenna for hf may forgive the uhf but not likely to work but not the other way round.

Using the wrong antenna will not be efficient and in higher powered radios it will cook the final transistors. Maybe even in lower powered stuff if used continuously.

I am not a professional so take my advice with that in mind. there are people out there with the knowledge but be prepared to pay if it means that much to you.

hope this helps and I welcome any critical advice from you other blokes out there.

AnswerID: 358062

Follow Up By: Member - Graham H (QLD) - Saturday, Apr 04, 2009 at 20:26

Saturday, Apr 04, 2009 at 20:26
A 27 mhz is a totally different thing to an HF radio

Firstly its an AM and presumably as you can buy one for a couple of hundred dollars it wont be quite as good as a $3500 Codan or Barret HF .

He said he has two aerials.

Most aerials are tuned to the frequency or as in an HF come as tapped or autotune.

On a D band RT 5mm can make a big difference in signal quality.

ALL RT'S need a good earth to stop interferance.
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Reply By: Member - Bentaxle - Saturday, Apr 04, 2009 at 21:29

Saturday, Apr 04, 2009 at 21:29
Check your grounding of the antenna, remove and reseat clean all contacts between antenna base and mount.
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AnswerID: 358079

Reply By: MEMBER - Darian (SA) - Sunday, Apr 05, 2009 at 09:36

Sunday, Apr 05, 2009 at 09:36
To be expected I'm told (so say the experts I've encountered, that is) - 27meg CB's are one variety of HF radio and the electrics in modern cars are a scourge to HF - eradication of the source of interference can often be impractical, given the amount of work and mucking around involved - many users of long distance comms gear just scan for selcalls during the day while mobile - you can then stop if you get a call. Much of the real 'comming' is done first thing or later in the day, while the car is still restingly quietly and something is sizzling on the campfire :-o)
AnswerID: 358145

Reply By: anglepole - Sunday, Apr 05, 2009 at 10:03

Sunday, Apr 05, 2009 at 10:03
A modern AM car radio has a sensitivity of about 18db/signal to noise of 10db. (This why you don't hear much vehicle noise)

Your 27mef CB probably has a sensitivity of 0.5 db for the same S/N ratio therefore picks up lots of noise.

Unless the noise is coming through the supply volts to the radio (this can be easily checked by running the radio off some dry batteries) you may require heaps of work to track down the electrical noise.

Vehicle noise can be generated from many sources ie Ignition for petrol engines, meters (oil,fuel), alternator, vehicle computers even wheel bearing etc.

Try here first for some help

If you need to use this radio probably some professional help may be required
AnswerID: 358154

Reply By: Member - Graham H (QLD) - Sunday, Apr 05, 2009 at 14:24

Sunday, Apr 05, 2009 at 14:24
I read an identical post on another forum and the advice was the same as well so I guess both lots would be fairly near the mark...

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