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eHam Forums => Mobile Ham => Topic started by: KB3CDF on May 14, 2001, 07:54:18 AM



Title: Bad Rectifier in Alternator OR Ignitian Noise???
Post by: KB3CDF on May 14, 2001, 07:54:18 AM
Question:
I recently installed a 3/4" hole mount for a NMO antenna.  I expected to find a more efficient antenna system in result.  Apparently, I have over achieved. I now TX & RX an alternator type whine in the signal (144MHz/440MHz) that rises and falls with the RPM.  The same exists in the HF & commercial AM.  The noise wasn't noticed until the new antenna system was installed.

Please help...  I would like to eliminate the noise or seriously impede it.

Vehicle Description:
1999 Chevrolet Blazer, 4.3l Vortec Engine, 4 Dr, 4WD, LS (S-10) chassis...

Power Source:
Direct from the battery...

~~
John DE KB3CDF/M + Whine


Title: Bad Rectifier in Alternator OR Ignitian Noise???
Post by: AC5WA on June 05, 2001, 11:53:15 AM
It is quite likely that you have created a ground loop through your antenna lead.  The tranciever is probably grounding through the shield of the antenna lead as well as through the common (-)power lead.  One way that you can sometimes reduce this is to improve the ground (common) connection between the radio and the (-) battery.  There is probably significant voltage drop in the power connection to the radio. This will make the noisy coax shield a better DC ground than the black wire.

Were you running a cigarette lighter plug and a mag mount antenna before?  If you were, your problem is that you stopped "inproving" too soon. The only DC ground was through the black wire because the antenna was insulated at DC by the paint on the car.  Improve your battery connection for power and I believe your noise will go back down.

Good Luck!
AC5WA


Title: Bad Rectifier in Alternator OR Ignitian Noise???
Post by: W8JJW on June 06, 2001, 12:31:57 PM
Make sure the chassis of the radio is grounded well and separate from the battery ground..should be short as possible to a good ground.

Good Luck  73 John