UHF Interference

Submitted: Sunday, Oct 05, 2003 at 20:52
ThreadID: 7621 Views:3444 Replies:3 FollowUps:2
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Hi All,

I am having a little problem with my UHF. Whenever I put my lights on to high beam there is an interference niose.

Does anyone have any ideas??

Thanks in advance.

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Reply By: Tuco69 - Sunday, Oct 05, 2003 at 21:51

Sunday, Oct 05, 2003 at 21:51
Wire your UHF positive (red) direct to the battery. Wire the UHF negative (black) to an earth point as close to the UHF as you can. Keep the black earth lead as short as possible.

AnswerID: 32842

Follow Up By: Radar - Monday, Oct 06, 2003 at 12:28

Monday, Oct 06, 2003 at 12:28
Thanks for the infor Tuco. I'll do it tonight.

Much Appreciated.

FollowupID: 23510

Follow Up By: Tuco69 - Tuesday, Oct 07, 2003 at 10:47

Tuesday, Oct 07, 2003 at 10:47
G'day Radar - what I have suggested is not a guaranteed cure - but has worked for me on three different vehicles.

In all cases the UHF's were originally wired (as recommended) direct to the battery - BOTH pos and neg leads. In all cases, alternator noise that increased with alternator output (eg lights on) was getting into the radios. In all cases, line capacitors (suppressors) were fitted to the positive leads close to the radio - with no reduction in noise. In all cases, removing the long earth direct to the battery and cutting it short and fixing to a good earth point close to the radio fixed the problem.

I have also now done the same with my Barrett HF setup and now enjoy noise free HF when mobile. This was not possible prior to shortening the earth lead. Another 'plus' when doing this is that you in effect are eliminating most of the earth lead by using the body/chassis for the return path. In high current situations like HF radio or 3 way fridges, you also are eliminating almost half of your potential voltage loss through the wire. Net result is better voltage at the appliance.
FollowupID: 23564

Reply By: chrisfrd - Monday, Oct 06, 2003 at 21:58

Monday, Oct 06, 2003 at 21:58
Hang on! MORE INFO please!

Firstly, what is the truck? How old is it? How old is the battery? What condition are the electrical systems in?

I'm presuming that you have the engine running when the high-beam lamps are on. Am I correct?

If the engine is running. then the interference that you are getting is probably from the alternator and the associated rectification systems that you have. Modern rectifiers are built into the alternator housing, whilst older trucks have the rectifiers as a separate system, bolted onto the firewall, (the old 40's and 60's were like that by memory, but I have only ever worked on Patrol's and newer Cruisers.

If you are having noise problems only when the engine is running, then your rectifier, (regulator or such) are faulty or at fairly high load levels. Some older regs clicked and buzzed so much it was like listening to a chain-saw! If this is the case then there are a few things, (short of renewing them), that you can do to sort it out. Firstly, on older Petrol trucks, have the ballast resistor checked and renewed if suspect. Secondly, check the capacitor on the distributor checked and renewed. Then, move to the alternator and the regulator.

If this doesn't sink it, then you could be getting RF based interference from somewhere in the car. This is uncommon on UHF though, as the FM operation of the radio lends itself to better noise suppression.
AnswerID: 32928

Reply By: Eric Experience. - Tuesday, Oct 07, 2003 at 23:04

Tuesday, Oct 07, 2003 at 23:04
AS others have stated the extra current from the alternator is the most likely reason. there are lots of ways this can be improved, a supressor on the alternator is one, the way the coax is run is important, if you run the coax under the mudguard and not through the engine compartment that will help, runing an earth wire as short as possible from the antenna base to the body helps. IF you do all of the above and still have the problem consider a ground idependant base, Eric.
AnswerID: 33068

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