Hi, Robby — 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).
At least one manufacturer sells a kit (priced in the $100-$200 range, plus local labor) that is meant to be installed at the air handler by one of their authorized dealer's techs. Whether it's effective or not, I can't say, and you might be able to convince them that as a long-time radio amateur you can do the installation yourself. Be very careful about assumptions as to the source of the noise; so much of the wiring between the various components of the A/C system is unshielded that it's hard to say for sure until you do some detailed "sniffing" with an AM radio or other suitable detector. I doubt, for instance, that an HF beam can distinguish between the direction to the compressor and the direction to portions of your interior wiring. In the system I mentioned above, in that residence the peak noise pickup was around the thermostat on a hallway wall on the first floor of a two-story (plus attic) building. You'll probably do better with this kind of question on the RFI reflector. I suspect the K3 is incidental to the issue. Bud, W2RU On Apr 30, 2012, at 8:20 AM, Robby.VY2SS wrote: > Riddle me this! > > I have strong interferance since installing an air source heat pump. It is > most annoying on 20M. It is also present on 40M and 15M. My 40M antenna is > twice as far from the compressor and the noise on that band is reduced. On > 20M is is S3-4. It used to be S1. Here is what I have done in trying to > eliminate this problem: > > 1. I removed the 220VAC from the compressor at the breaker panel. The noise > is gone. > > 2. I turned the breaker back on and put my indoor units on fan only. The > noise is gone. I guess this proves the noise is coming from the compressor. > Also when I turn my beam toward the compressor the noise increases. > > 3. I disconnected my power supply and connected the K3 to a battery. The > noise is gone so It is not coming in on the house AC circuit. > > 4. I disonnected the antenna at the K3. The noise is gone so it seems it was > coming from the antenna. > > 5. I reconnect the antenna and turn the RF gain to zero. The noise is gone > from the speaker but on the waterfall it is NOT gone. > > I am hearing a buzz in the speaker or headphones and can see many vertical > lines on the P3 waterfall. The wider my bandwidth setting the more noticable > problem but the lines are there for the entire width of the P3 scan. Maybe > 40 lines on P3 display with a 5 khz scan width. > > I have tried placing 3 capacitors across the 220VAC terminals where it > connects to the compressor. L>G, L>N, N>G with no measureable results. > > I would be very happy if someone can shed a little light on this. > > 73, > > -Robby > VY2SS ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
