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Author Topic: How I cured Noise on GM Diesel  (Read 415 times)
AB5CC
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Posts: 47




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« on: October 12, 2002, 06:42:48 PM »

I just wanted to post this in hopes it will help others plagued with noise on a mobile installation.  I am running an IC-706 in a GM 1-ton Diesel pickup.  I figured that the diesel would be friendlier to mobile HF since there is no ignition, but I was wrong.  When I installed the radio, the best noise level I had was a constant S5 motorboating, puttering sound that the noise blanker wouldn't take out.  The worst that I had was a constant S9 static noise.

I took 3/4" braided ground strap and self-tapping screws and bonded all parts of the underside of the truck together.  This did not help.  Then I found a 2" diameter torroid in my junk box.  I do not know the material.  It is one of those with red enamel paint on it.  I wound 6 turns of the coax (RG8X) thru it about 3 feet from the inside connector.  This completely stopped the noise.  Not even an S1 without the noise blanker.  Needless to say, I am very happy that it was this simple.  This particular diesel has the mechanical injector pump so I think the noise came from the fuel pump.

Hope this helps someone.

73, Kenneth (AB5CC)
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K0BG
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« Reply #1 on: October 14, 2002, 09:52:02 AM »

Induced noise from the various electrical noise in any vehicle is a commmon problem. Your solution worked, but I'm not sure why.

The toroid you used appears to be a T200-2 (red coded iron) It has a very high cutoff>30 Mhz), rather low permeability (10), and I'm surprised it worked.

The common method utilizes snap-on ferrite beads made of 43 material. This mix has a cutoff of 1 Mhz, rather high permeability (250), and acts like a large resistor to frequencies over its cutoff. Since DC circuits are rather low impedance (a few hundredths of an ohm), the additional 80 to 100 ohms added by the bead becomes significant. Hence they isolate the circuit from induced high frequency noise.

I suspect you might have had a bad connection which was repaired when you installed the torroid.

Alan, KØBG
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