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Old 08-25-2009, 09:41 AM
leiniesred leiniesred is offline
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Default Dealing with Vehicle interference? (whine)

Last weekend's sale at HRO and patient money saving finally let me get a mobile rig in the ol' 4Runner.

Yaesu 7900 under the seat. Antenna on the back corner of the passenger bed rail. Display fits in front of the switches in the center console. Mic on the radio pod. Power runs all the way to the battery.

The power cables route right over the high frequency Pulse Width Modulated DC fan controller. (I only have an electric fan on my 4runner).

On receive, and presumably transmit, I can hear the fan controller increasing and decreasing the fan RPM (thermal feedback ckt maintains radiator temperature by adjusting fan RPM.) The result is an alternator type whine that increases and decreases slowing while sitting at stop lights.

How to fix? This isn't technically an alternator whine problem, but it is similar. I don't think there is a diode on the fan. Proabably should be.
Am I picking up the noise on the power wires? can I slap a torroid on the power wires? Some kind of sheilding on the power wires? big ol' diode on the fan?
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Last edited by leiniesred; 08-25-2009 at 10:07 AM.
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Old 08-25-2009, 10:09 AM
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nakman nakman is offline
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sounds like you need a whine filter. http://www.risingsun4x4club.org/foru...ead.php?t=9852
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Old 08-25-2009, 10:40 AM
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Attachment 14359
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Last edited by DaveInDenver; 08-26-2010 at 09:15 AM.
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Old 08-25-2009, 11:13 AM
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DaveInDenver DaveInDenver is offline
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Quote:
Originally Posted by leiniesred View Post
How to fix? This isn't technically an alternator whine problem, but it is similar. I don't think there is a diode on the fan. Proabably should be.
Am I picking up the noise on the power wires? can I slap a torroid on the power wires? Some kind of sheilding on the power wires? big ol' diode on the fan?
Yeah, you probably need the diodes to shunt the switching FETs, but you will still need some capacitance for the bypass and to filter. Think of the problem as two different issues, one is to damp switch transients and the other to filter the ripple. So bulk capacitance (and I mean bulk, monster caps, like a couple of 100uF computer caps) across the PWM supply to give the transistors plenty of charge to work with, diodes to suppress the EMF transients and finally a straight forward LC filter to quiet the switching ripple.
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