UHF interference

Submitted: Tuesday, May 13, 2003 at 20:01
ThreadID: 4891 Views:1379 Replies:3 FollowUps:2
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Hi guys, have just fitted a HI-6 ignition system to my duel fuel GQ and seem to have solved my tuning problems with the LPG but the unwanted side effect is interference on my uhf. Can anyone sugest any suppressor or another way of fixing the problem.
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Reply By: Tuco69 - Tuesday, May 13, 2003 at 20:33

Tuesday, May 13, 2003 at 20:33
First the way that the unwanted interference is getting into the UHF needs to be established. Is it coming in through the positive power supply, the earth (negative) or is the aerial picking it up and coming in that way.

To eliminate the aerial - simply unplug the aerial from the UHF and see if the noise is still there. If it is then do away with as much (negative) earth wire as you can, Shorten the earth lead on the radio and secure it to a good earthed point close to where the radio is mounted. The shorter you can get the earth lead, the better. If this doesn't cure it then the positive supply is probably the source of entry and either a filtered lead or capacitor close to the radio may help. Make sure that the positive supply is direct to the battery and not from the vehicle loom or accessory circuit, and also try to keep the positive supply away from the ignition system that you suspect is creating the noise.

Tuco in Cairns
AnswerID: 19919

Follow Up By: bozo - Tuesday, May 13, 2003 at 20:48

Tuesday, May 13, 2003 at 20:48
Thanks Tuco, i'll look into that. I think that I did wire it into the original harness from memory.
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FollowupID: 12687

Reply By: Member - Nigel - Friday, May 16, 2003 at 07:09

Friday, May 16, 2003 at 07:09
Another school of thought suggests running a good size twin cable direct from the battery for both positive and negative to the radio.

The theory being that the battery is a good filter of electrical noise, so if you radio is the only thing on the cable direct from the battery then less chance of noise.
AnswerID: 20178

Follow Up By: Tuco69 - Friday, May 16, 2003 at 10:54

Friday, May 16, 2003 at 10:54
Nigel - I agree that the battery is an excelent capacitor. But any capacitor fitted should be as close to the radio as possible. This would mean either mounting the radio under the bonnet beside the battery or moving the battery into the cab to beside the radio. Neither situation is desirable or practicle. The idea of the capacitor is to remove (filter) the noise that is coming in via the 12 volt supply. The noise may be coming in either on the positive or negative supply, although many manufacturers of comms equipment may already have inbuilt filtering (capacitors) where the 12V positive supply enters the unit. This also applies to many car radio head units. If the earth can be made as short as possible, then that path is reduced. Voltage losses can also be reduced by not running the earth wire to the battery, but using the common body/chassis earth instead. Much the same goes when wiring a camper trailer battery to be charged from the vehicle. Voltage loss applies to both the positive and negative supply.

Tuco in Cairns
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FollowupID: 12918

Reply By: bozo - Friday, May 16, 2003 at 11:49

Friday, May 16, 2003 at 11:49
I am going to try a combination of things, I'll run a cable directly to the battery and also fit a suppressor because there is a bit of noise on the car radio on AM as well. Thanks for all your advice guys.
AnswerID: 20198

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