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Don - KM4UDX
A few notes:
1) when I added a expensive low noise top quality high volume fan, I got paint all over the waterfall on all my favorite bands. The RF hash/noise was "substantial". It was easy to test...fan off => noise off, and fan on => noise on. When I replaced the high priced boutique fan with a $2.99 cheap-o-fan, the noise stopped, and the air flow continued.
2) You may yearn for a more sophisticated approach where the fan only runs on TX. Which of course is only logical. Avoid that line of thinking. Your hard wired fan is now a nice adjunct to your power on light. Fan on => power on.