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Author Topic: Clicking in IN bound audio even HT's?  (Read 418 times)
K6SRP
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« on: May 19, 2009, 08:54:40 AM »

I have a 2000 Chevy Astro Van and recently just installed a rig in it, the inbound audio has an alternator like sound that clicks and the speed of clicking (Frequency of clicks) is tied to engine revs.

I tired everything to get rid of the noise, got a new radio and same thing, it was driving me nuts.

Then last night I got in the van with my Icom HT

HT was running on internal batteries and using the stock ant on the HT so the HT was in NO WAY connected to the van, just sitting in the cab with me, and that dang clicking is there just as loud as my installed rig!?!?!
So it seems the van is creating some massive RF interference inside and outside the vehicle?

It's evident only when squelch is open BOTH in 2 Meter and 70cm

Any ideas?
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K0BG
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« Reply #1 on: May 19, 2009, 07:42:31 PM »

About the only RFI capable of being heard on an FM radio (assuming it is properly designed), is that caused by the high-pressure fuel pump. They're piezo controlled, and their output does have some FM deviation. It sounds like a slight purring sound (not unlike alternator whine). Since it is also switched off and on, it is possible for it to generate a popping noise similar to ignition noise.

Is there a cure? Maybe, but you have your work cut out for you, as you have to remove the pump (it's in the fuel tank). You can put ferrite cores (mix 31 is the best) on the wiring harness, but you might not be able to get rid of all of it.

Alan, KØBG
www.k0bg.com
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K5LXP
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« Reply #2 on: May 20, 2009, 11:18:01 AM »

Dunno if I go along with the fuel pump theory.  In my experience they produce a "hash" when they run.  I've never heard one at VHF.  Alan's theory assumes a perfect FM demodulator.  You cram enough AM (broadband pulse) into a real world FM receiver, and something's going to come out.

However, I *have* heard ignition and fuel injector noise riding on top of received carriers on 2M FM.  Put a "sniffer" antenna on your HT and see if you can find a source of emanation by waving it around different points of the vehicle.


Mark K5LXP
Albuquerque, NM
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K6SRP
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« Reply #3 on: May 20, 2009, 07:48:56 PM »

Hmm Some others on another site seem to think the noise is from the coil packs as it's tied directly to engine speed.
There were suggesting a bad spark plug or wire grounding out to the chasis?
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K6SRP
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« Reply #4 on: June 02, 2009, 05:27:41 PM »

This was due to a VERY worn and melted Distributor cap and rotor.
Replaced these two items and alas SILENCE!
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K5LXP
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« Reply #5 on: June 02, 2009, 07:51:57 PM »

Thanks for posting a followup. It may give future readers a place to start looking.

Mark K5LXP
Albuquerque, NM
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