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Author Topic: Ways to minimize RFI in an apartment  (Read 1998 times)
KA0ERZ
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Posts: 18




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« on: March 09, 2006, 07:17:25 PM »

I've been out of HF for a long time and am now in the process of choosing an antenna to install in the attic.  Most likely it will be a 2-3 band dipole or short vertical.  I have an IC-718 (100w or less) and a low-pass filter and will use one of the 100% braid coax's.  From what I remember, with modern radios, the issue is almost always the cheap consumer electronics and not the transmitter.  If thats not correct, let me know, otherwise is there anything I can do to minimize RFI to my stuff and the neighbors other than reducing power?  I'd also be interested in how much power, up to 100w, people have been able to use in apartments or condo's without causing intereference.

Thanks
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K4SAV
Member

Posts: 2505




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« Reply #1 on: March 30, 2006, 01:32:55 PM »

RFI works both ways, interference from your transmitter to consumer products, and RFI produced by the consumer products to your receiver.  With an antenna in an attic, you are likely to have both kinds.  For a preview of what to expect on receive, attach a piece of wire to your antenna terminal, run the wire around your room, and listen (don't transmit). The stuff you hear will be representative of what you will get with your attic antenna, plus or minus some amount of amplitude.

If you are typical, you can also expect to interfere with some devices when transmitting. The amount of power required to do this can vary a lot. Some devices may even have problems with QRP levels. There seems to be an endless list of devices that may be effected. To give you one example, I remember putting up a 102 ft dipole that ran over one corner of my roof, about 15 ft above the roof. It took 30 watts to set off the alarm system and blast the intercom. I have no doubt that if the antenna was in my attic, it would have caused problems at 5 watts, because it would have been in very close proximity to the intercom and alarm system wiring. Others may not experience problems from these devices, it depends on how much RFI filtering the manufacturer uses. Many devices have no protection at all. There are two ways to fix this, move the antenna, or go to the problem device and install RFI filters. This may be doable if the device belongs to you, but if it is in a neighbors condo, good luck.

The quickest and easiest fix for RFI filtering at the problem device, is to use snap-on ferrite beads, with as many turns of wire on the bead as you can get.

I wish I could suggest a good way of going about doing this, but it can be difficult dealing with neighbors who don't understand the problem, and are convinced that you are the problem. Come to think of it, we may all be in this boat if BPL ever gets fully implemented.

Jerry, K4SAV
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