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rf noise from cooling fan control circuit

ian
ian Member
edited December 2014 in FLEX Series (Legacy) Radios
When the heat sink temperature increases and the cooling fans speed up my noise floor level on six meters increases by 20dB.  Only when heat sink temperature has been reduced and the fans slowed down does the NF drop back to normal  The radio has been to Flex Germany but still has this issue, I have been told by Flex that this "MAY" be solved by the next firmware update. Been having this issue for 10+ months, a friends flex3000 shows similar issues. Fans have been changed but I believe the issue is with the PWM driver circuit for the fans and the noise waveforms alters with the fan speed.  This noise can be heard from at specific frequencies between 20 and 60Mhz and is the same into a dummy load or an antenna

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