One of the nice things about teaching the General class is that I actually learn a few things from time to time. For example, last Tuesday, we covered RF safety, a topic that was definitely not on the test when I took my General class test 30 odd years ago. In order to adequately explain the topic to my charges, I had to do some quick boning up of my own.
I found out some interesting things. For example, the resonant frequency of the typical human body is somewhere between 30 and 100 MHz. That’s why the maximum permissible exposure (MPE) for that frequency range is so much lower than the MPE at 1.8 MHz. It’s so low, in fact, that the FCC guidelines state that you must perform a routine RF safety evaluation if you are outputting more than 50 W on the 10m band. For comparison, note that you don’t have to do this evaluation if your output power is 100 W or less on 15m, 225 W on 20m, 425 W on 40m, and 500 W on 80m.
Not sure what’s required to comply with FCC Guidelines? Well, if not, you’ll want to pick up a copy of Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields, OET Bulletin 65. Supplement B of this publication deals with information for amateur radio stations and includes worksheets that step you through the process. You can get it by mailing the FCC or from the FCC website. It’s a pretty large PDF file, so you might not want to attemp it unless you have a broadband connection.
Going through this material really got me thinking about my own installation here. I’ve been thinking about a tower, but now I’ve pretty much decided against it. One reason is the lay of the land here. My house is situated on a hill, and my neighbors to the rear are uphill of me. A beam on a 50-foot tower would probably beam right into their house when pointed in that direction. Couple that with the difficulty in erecting one in the first place, and I think that I’ll just forget about it for now. It may just be time to move to a better antenna site…..errrrr, new house anyway.
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