On 4/30/2012 6:13 AM, W2RU - Bud Hippisley wrote: > The noise is very likely coming from the pulse-width modulation (PWM) > circuitry that runs the blower motor located in the air handler enclosure > (often located in the attic or on the top floor of a residence). In poorly > designed and shielded circuits the noise can escape from that enclosure out > into other parts of the A/C system — riding on wiring to the thermostat(s) on > the walls and on power leads to the outdoor unit. In one installation I saw, > the air handler enclosure in the attic provided a very good shield, > preventing direct radiation from the circuit. However, the high frequency > energy from the PWM was leaving the enclosure and radiating to nearby > antennas via the thermostat wiring (and to a lesser degree, the power wiring > to the compressor).
This is an excellent description of what is likely the mechanism causing your problem, and so is Bud's suggested solution. This is yet another example of the manufacturer leaving out the parts needed to prevent RF noise. In this case, they even have the balls to charge extra for them. I also concur that the RFI reflector is a good resource for this kind of problem. There's an RFI tutorial on my website. http://audiosystemsgroup.com/RFI-Ham.pdf 73, Jim k9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
