Doug, The solution is to replace the noisy fan with one that is designed for very low EMI. The first thermostatic switch controlled fan I put on my solar-powered UHF repeater had a whine that modulated the carrier. I then swapped it with a Panasonic fan that was specified for low EMI. Presto! There was no trace of fan noise on the carrier.
Part of the problem is the basic design of some RF-noisy fans. Hall-Effect devices are used for commutation, and some designs are inherently noisy. Some of the noise is conducted, and some is radiated, so ferrite rings, series inductors, and capacitors are of little value in filtering the noise. Just choose a low-EMI fan in the first place! 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Doug Hutchison Sent: Tuesday, April 17, 2007 7:09 AM To: [email protected] Subject: [Repeater-Builder] Problem with fan noise in power line. Have a system comprising 4m simplex link and 2m repeater running from same PSU. Tried using a brushless fan to boost cooling but when running and connected on the same PSU as the RF kit, the noise generated on 4m TX audio (not 2m), a very loud buzz, is incredible. Obviously the inverter noise is being carried back into the PSU so some sort of filtering is needed as, when the fan is run on a separate supply, there is no problem. Has anyone encountered such a situation and if so what circuit or device was used to cure the noise (other that a second PSU)? Regards, Doug - GM7SVK
