HF interference from speedo fix?

Submitted: Thursday, May 22, 2008 at 18:21
ThreadID: 57895 Views:2028 Replies:2 FollowUps:4
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Hi all,
I'm getting interference over my barrett HF when the car is mobile. No problems with the engine running (1hz diesel 80 series)when stationary, only when driving, so must be coming from the impulse sender at the gearbox or the speedo.
Has anyone else experienced this and is there a way to fix it?
Tony J
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Reply By: Peter 2 - Thursday, May 22, 2008 at 18:36

Thursday, May 22, 2008 at 18:36
I think you will find it is the oil pressure sender, that was what it was on all my cruisers.
Stays quiet till the oil pressure changes and then starts making a whirring whining noise. Can be cured by putting a capacitor between the centre terminal and the case of the sender. It is on the side of the block towards the rear of the engine on passengers side, tin shaped thing about 30mm dia.
you can prove what it is by unplugging the suspect unit and going for a drive.
you will also find the wiper motor, GPS cpu and even the UHF CB will cause noise.
AnswerID: 305330

Reply By: Member - Mark E (VIC) - Thursday, May 22, 2008 at 23:10

Thursday, May 22, 2008 at 23:10

Can you describe what the noise sounds like and on what frequencies on the HF,

I have a 105 series and a Codan HF and I get a 'beeping' noise which varies only with the speed of the vehicle, irrespective of engine revs, so it's not engine, alternator or anything else causing it. The beeping noise is faster than wheel rotation so I figure it is something like tailshaft rotation (not too sure if there is anything electronic attached to tailshaft). I can stop the car and get a long continuous beeeeeep or move forward a couple of inches and it goes away completely, in between beeps (if that all makes sense!?!).

I still haven't found what's causing it yet, but I'm guessing it is something like the sensor for the speedo as well. Mine only happens on one frequency 7999 kHz, which is why I haven't sorted it yet.

Interested to hear more about yours and any fix that may be suggested here....C'mon Footy, I know you're onto it...!


AnswerID: 305372

Follow Up By: traveller2 - Friday, May 23, 2008 at 08:29

Friday, May 23, 2008 at 08:29
Try unplugging the speed sensor from the transmission, that should isolate it.
FollowupID: 571395

Follow Up By: Stu & "Bob" - Friday, May 23, 2008 at 14:53

Friday, May 23, 2008 at 14:53
Do you have ABS on your 105? It could be coming from one of the pickups on the wheels.

BTW, I have a 105 pov pack, and I get no interference whatsoever (apart from "normal" HF hash)
FollowupID: 571471

Follow Up By: Tony J - Saturday, May 24, 2008 at 06:45

Saturday, May 24, 2008 at 06:45
Hi Mark,
The noise mine makes is just like what Peter 2 describes in the post above your reply. I hadn't considered the oil pressure switch as I can rev the engine (to increase the volts from the alt. to max) and the whine is not there. I would assume that there would be a pressure difference between idle and 2000 revs. Nevertheless, I'll try the capacitator on the oil sender just in case. I have no idea on what your noise could be coming from, sounds very weird. Some years ago I change the power lead in the car fridge to some you-beaut cable to reduce the interference the fridge was causing when it was running, yeh, sorry, no idea what would cause that noise.
FollowupID: 571589

Follow Up By: traveller2 - Monday, May 26, 2008 at 08:04

Monday, May 26, 2008 at 08:04
The oil pressure sender only makes anoise when the pressure is changing rather than when it is steady.
It's the reverse of what you would think.
FollowupID: 571955

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