Let me introduce my self. I am a ham radio operator of 45 years and a RF engineer for a major cell phone carrier. I live in Rural - Elizabeth, Colorado. I started to receive a sweep pulse type of interference in January 2004 in the HF band. It sounds like a click on the audio and pumps the AGC quite hard.

I found the problem to be a Perfect Fit electric blanket at a neighbors house about 1/4 mile away. The power supply/blanket is radiating about a 3000 uV signal as measured on my spectrum analyzer at 30 meters with a reference loop antenna. The sweep signal is from 2-60 MHz in a 1-2 second sweep. The power supply was connected to an electric blanket pad supplied and hung vertically. The blanket makes a nice loop antenna. This power supply is clearly in violation of part 15.907 rules for none radio devices. The ruling states that a non radio device may not emit more than 100 uV at a distance of 30 meters from 2-30 MHz. I contacted Perfect Fit Industries and they have not gotten back to me about the problem. It is my understanding they have placed this sweep frequency radiation through the blanket to sense when some one has gotten into bed in order activate the power supply. Nice idea in China but a non starter here in the US. Besides the interference problem, there is the RF exposure factor to be mitigated for human exposure. Does OSHA know about this?

These blankets are being sold everywhere in the Denver area and I would imagine this is also the case over most of the USA. This has a greater potential for combined HF interference than BPL. The aggregated signal combining of several blanket power supplies, times households in the neighborhood could bring the noise level on your HF transceiver to S9+40 dB. A single blanket received on my beam antenna placed the sweep interference at S9+25 at a distance of 1/4 mile. This was observed from 13-30 MHz. On a center fed ZEP the signal was S9+10 from 1.8-14 MHz.

Now normally a rapid sweep of this signal can be eliminated with a good noise blanker if there is only one source and you don't mind the front end overload and IMD from having the noise blanker on all the time. I found that when there are several of thes blankets in operation your noise blanker will not be able to keep up with the aggregated pulse sweeps. I bought the neighbors a different conventional blanked to replace their Perfect Fit brand in order to use my station and returned the DEFECTIVE blankets.

Several things must be done to rid the country of these blankets.

We must be ever vigilant to interference of our radio spectrum. Even if you are not receiving interference it is only a mater of time before someone gets one of these fuzzy sweep generators.

73's

Mike Higgins - K6AER