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Author Topic: Keeping RF out of the living space  (Read 9653 times)
K0JEG
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Posts: 580




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« on: March 11, 2013, 06:31:22 AM »

I'm planning on installing my trusty old AEA ISOloop in the attic, along with a vertical 2M/70CM co-linear. It will be about 18' above the floor of the house, and I intend to run all network, phone and TV coax in the crawl space. This will be similar to a setup I had years ago when renting (although I had a balcony and no restrictions on outside antennas at the time), so I'm familiar with some of the compromises and issues that come up. When I was renting I always had a heck of a time keeping RF out of my stereo, especially the powered subwoofer. In the new place there's a couple of metal vent pipes and a gas fireplace flue going through the attic. The ISOLoop will only handle 100Watts and I don't really have any plans on increasing power down the road (although I might add a 40/80 meter loop and or a 6 meter dipole at some point). I plan on grounding all antennas and coax the same as if they were installed outside, all bonded to the electrical ground.

Should I also plan on grounding the various vent pipes? What about shielding the floor of the attic with something like chicken wire (grounded as well)? While I don't think there's going to be any major problems, I'd just like to avoid any minor inconveniences down the road.
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WB2WIK
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« Reply #1 on: March 11, 2013, 10:05:52 AM »

I'd never use chicken wire or anything else on the attic floor, that will restrict the way the loop antenna works.

I've always dealt with interference problems at the receptors, not the emitters; i.e., deal with each receptor individually until there isn't any interference.

I wouldn't bother grounding the vent pipes and chimney flue, either, frankly.  You'll never achieve an RF ground at such an elevated point, and adding a "DC" ground isn't necessary.
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K0JEG
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« Reply #2 on: March 11, 2013, 11:36:37 PM »

Thanks for the advice. I figured it was all overkill, but you never know. Much easier to type it out than do it and find out it doesn't make a difference (or make things worse). Smiley
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KF7CG
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« Reply #3 on: March 19, 2013, 10:15:38 AM »

if your place is like my 7 year old house, no way to ground any of the plumbing! Every last scrap of it is plastive of one sort or another.

Things have change a great deal since the days of galvanized iron pipe and copper for plumbing. No cast iron pipe or chromed brass in the waste water plumbing either; just PVC or CPE.

KF7CG
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WB6BYU
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« Reply #4 on: March 20, 2013, 12:59:38 PM »

Put a filter on the audio cable to the sub-woofer, or add an internal
capacitor so it doesn't respond to RF (which it shouldn't.)
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W8NF
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Posts: 53




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« Reply #5 on: April 01, 2013, 03:36:30 PM »

Unless your house is very old, NEC code requires all exposed metal (except screws, nails and other fastening hardware) to be bonded to the service ground.  This would include any metallic vents, metal plumbing and drains, etc.

Subwoofers are a pain.  They're all poorly designed, RFI-wise.  I simply put them on a power strip, so that when they are off, they are off.  There is no time when I'd be on the air, and the stereo in operation anyway.

I agree with others...anything you do to attempt to screen the attic floor would:
1) Not do much: at low frequencies, that screen has to be sizeable in terms of wavelength to do any usesful screening
2) Impair the antenna operation.

In RFI remdiance, you can
1)attack the source (usually not a good idea, since your goal for the source is maximal radiation)
2)attack the coupling mechanism (this is the purpose of ferrites on cables, etc)
3)attack the victim - bypass capacitors at the inputs and outputs to audio gear, etc.

Hope this is useful

Dave W8NF
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