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Author Topic: Attic Dipole = Shack RF = GFI Issues And More  (Read 9961 times)
KD0PCJ
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Posts: 18




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« on: August 01, 2012, 08:34:30 AM »

Like many hams, I live in a covenant-restricted "snooty" neighborhood, and like some, I have turned to my attic to hide my antennas. Of course, there are consequences - shack RF, among others.  I keep my RF power output down as a result, and test as required.  I discovered that on certain frequencies (20 & 40M) and at certain wattage outputs (when I kick my low power linear on), there can be enough RF crawling through the wiring to trip my GFI's. I was popping my XYL's whirlpool tub GFI in my main panel, and popping my kitchen and bathroom outlet GFI's. Research indicated that this is especially likely in homes built before 2004.  After that year, electrical standards changed and GFI's were built to be better insulated from RF. After upgrading my 1998 GFI's to modern versions, no more problem.  I hope this helps other newbies in the same situation.       
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KD0PCJ
Member

Posts: 18




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« Reply #1 on: August 01, 2012, 07:14:04 PM »

Additional: If you need more information or have a different problem, there are more threads that discuss GFI related issues, just do a search.  Check the RFI/EMI Forum particularly. This is pretty common, even for those who are fortunate to have external antennas.  RF gets in to everything, right down to the PC keyboard and mouse...I had to switch to wireless peripherals to solve the problem when ferrites didn't work. 
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KA1LDD
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Posts: 10




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« Reply #2 on: August 23, 2012, 12:44:40 PM »

I also have an attic antenna which made every metal object in the shack very "hot" when I would transmit.  This choke from DX Engineering makes a world of difference==> http://www.dxengineering.com/parts/dxe-fcc050-h05-a 
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AB4D
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Posts: 296


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« Reply #3 on: August 25, 2012, 12:11:32 PM »

When you say low power amplifier, how much power are we talking about?  Second, you might consider an artificial ground, it helped with RFI in the house, when I was in your situation, and I kept my power to 200 watts or less (FT 1000D).

73.
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LNXAUTHOR
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Posts: 43




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« Reply #4 on: September 05, 2012, 03:32:29 AM »

yep, had issues in a townhouse i lived in - great antenna - inverted 'L' - 23-ft horiz, 45-ft vertical (wire dropped down a shrubbed brick wall)

but every time i used more than 20 watts on 20M, the antenna would trip my fire alarms! the security company was, let's just say, less than helpful - only lived there another year and now have a wire dipole up a tree out back - no more issues
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KQ6Q
Member

Posts: 964




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« Reply #5 on: September 17, 2012, 11:45:40 AM »

LNXAUTHOR -
If you can't make contacts on your attic antennas with 20 watts and less, you could consider temporary antennas in the back yard, removing them when you're not using them, or perhaps a screwdriver antenna concealed in a birdhouse, as has been described. If those aren't possible then you need to consider  'Radios in the Park' expeditions - get away from all the house wiring, and have a little adventure whenever the HF bug bites. Check out the QRP forum here. Meanwhile, use VHF in the house - get to know the folks on a few of the local repeaters. Perhaps even join a group that will let you use a remote base on HF.

Fred, KQ6Q
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KC9NRN
Member

Posts: 9




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« Reply #6 on: September 21, 2012, 06:10:35 PM »

Like many hams, I live in a covenant-restricted "snooty" neighborhood, and like some, I have turned to my attic to hide my antennas. Of course, there are consequences - shack RF, among others.  I keep my RF power output down as a result, and test as required.  I discovered that on certain frequencies (20 & 40M) and at certain wattage outputs (when I kick my low power linear on), there can be enough RF crawling through the wiring to trip my GFI's. I was popping my XYL's whirlpool tub GFI in my main panel, and popping my kitchen and bathroom outlet GFI's. Research indicated that this is especially likely in homes built before 2004.  After that year, electrical standards changed and GFI's were built to be better insulated from RF. After upgrading my 1998 GFI's to modern versions, no more problem.  I hope this helps other newbies in the same situation.       

I'm causing my expensive LCD TV to reset and my computer monitors to start beeping, I'm keeping output to around 100 watts now but need to get my antennas outside some how as well... should be fun!
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N4UP
Member

Posts: 23




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« Reply #7 on: October 17, 2012, 03:41:14 PM »

I have three semi-rigid multi-band rotatable dipoles in my attic and no RFI problems that weren't easy to resolve.  I have the three dipoles mounted on tripods, two at six feet above the floor with six feet between them, and the third mounted at 8 feet above the floor and in between the two lower dipoles.  I routinely operate at 600 watts on 10-40 meters with no problems.  Indeed, I have easily made about 4,000 contacts in the past six months and mostly DX.  Of course I have line isolators at each end of the feed-lines and the radio room is on the floor below the attic but not directly under the antennas.

One of the dipoles is for 40-20-15-10 meters and cut for CW, the second is also for 40-20-15-10 meters and cut for SSB, and the third is for 30-17-12 meters.

RFI problems.  Interfered with my DVR recordings until I added snap-on ferrite beads to the coax in to the DVR.  Interfered with my radio room computer until I replaced the wired mouse with a wireless mouse.  Set off my CO monitor until I moved it downstairs.  Interfered with my MFJ-998 antenna tuner, but that turned out to be RFI from the amplifier it was sitting on top of, so I simply raised the tuner an inch and the problem went away.  That's it.

Of course with attic antennas it depends on what else is up there and what the roof is made of.  I have a heating/air conditioning unit, duct-work, and lots of electrical wiring, and no problems with any of that.  But the attic installation did change the resonant frequencies of the dipoles, but mostly from proximity to one another.  There seems to be some sort of parasitic effect of having three dipoles in proximity, that seems to enhance their performance and increase the bandwidth.

And given the modest elevation ( third floor attic, about 35 feet above ground level ) I lose directionality, but that's okay because there's not enough room to actually rotate the antennas anyway.

Whenever I go above 600 watts strange things happen.  So I don't go there.  It doesn't seem to matter that the antennas and components and feed-lines are rated at much higher power.  But with 600 watts or so I have no trouble easily working almost anyone I can hear.  And sometimes I forget to turn on the amplifier and still make the contact at 20-40 watts.
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73, peter N4UP
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