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Author Topic: Eliminate RFI options  (Read 2621 times)
WB1FFI
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Posts: 19




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« on: April 18, 2012, 07:28:08 AM »

I have a Kenwood 440SAT exciter and a Heathkit SB-200 amp running into a Hygain 2 element tribander on a chimney mount about 30 feet above ground and several feet just above the roof top of a 2 story house. When transmitting mainly on 20 meters, my 2nd floor touch light dimmers go through their cycles and 2nd floor smoke alarm makes a funny buzzing noise. Will getting an antenna tuner help this situation which is not a big deal, but mildly annoying? If an antenna tuner would help, which model would you elmers recommend for my setup? If other suggestions, please let me know. I am limited by my antenna location and do not have any good options to move it. Thanks.
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AA4PB
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« Reply #1 on: April 18, 2012, 07:46:56 AM »

If your antenna is only a few feet above the roof then it is probably only a few feet away from smoke detector and power wiring in the attic. That's your problem - limited antenna to device physical separation. Your options are either to reduce the transmitter power output or to get the antenna farther away from the house. An antenna tuner isn't likely to help any.

If your smoke detectors are AC powered then you may be able to add some ferrite beads to the wiring to help or you could try replacing them with battery powered detectors to eliminate the AC wiring connection that is likely acting as an antenna to couple RF from your nearby antenna into the detector.

The easiest solution for the lamps is to replace them with lamps that have mechanical on/off switches.
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KE3WD
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« Reply #2 on: April 18, 2012, 07:56:57 AM »

Do you have a choke installed at the feedpoint of the beam to keep RF off of the coax shield? 

If not, you should.


73
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K1WJ
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Posts: 458




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« Reply #3 on: April 18, 2012, 08:08:34 AM »

Get a small plastic Folgers coffee can - wrap 6 turns of your coax around it - close to antenna feed point.

You could also make one on the radio side - with in 8ft of radio connection.

Run less power, if still issue - forget about an amp.

73 K1WJ David
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WA3SKN
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Posts: 5496




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« Reply #4 on: April 18, 2012, 11:15:56 AM »

You have a "fundamental overload" problem, and unless your coax is doing the radiating, filtering the antenna or using a tuner will not help.
Touch lights and smoke detectors are not supposed to be radio receivers.  You will need to filter the RF to keep it from getting into these units, or lowering your power levels.  Since moving the antenna is not an option, just lowering power by not using the amp would help.
But, filtering the touch lights and smoke detector is your best option.  Ferrites and/or bypass caps on all the wires going into these units should fix the problem. They are probably working as a "receive antenna", and letting the signals in. Check with the companys that made those units though... they might have some suggestions.
And the touch lights are notorious for RF sensitivity, so you may have to work at this!
Good luck with the project!
73s.

-Mike.
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W8JX
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« Reply #5 on: April 18, 2012, 11:56:57 AM »

Really need to reduce power or locate antenna further away from house. I do not believe that a choke is going to to do squat here. You are generating a very strong RF field in house.
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K5LXP
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« Reply #6 on: April 18, 2012, 03:02:57 PM »

Reduced fundamental RF at the devices and wiring can come in the form of increased separation, reduced power *or* better isolation of the affected equipment through ferrites or shielding of the affected devices.  It's not a given that all devices are susceptible to these field strengths and sometimes just basic RFI mitigation can effect enough isolation to have your cake, and eat it too.  Sometimes this involves a lot of iterative trial and test and possibly replacement of the more susceptible devices, but it is possible to create a high RF compatible environment.


Mark K5LXP
Albuquerque, NM
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W8JX
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« Reply #7 on: April 18, 2012, 05:50:19 PM »

If the RF level is that high forget the devices as I would not want to be a person in it either.
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W9GB
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Posts: 2626




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« Reply #8 on: April 18, 2012, 07:15:38 PM »

I have a TS-440SAT transceiver and a Heathkit SB-200 amplifier running into a HyGain 2-element triband antenna on a chimney mount about 30 feet above ground and several feet just above the roof top of a 2 story house.
Do you have this same problem with a barefoot (100 watt) TS-440S ??

Did you uses a balun/unun at that feed point of this HyGain antenna?

How are you preventing common-mode RF issues??
« Last Edit: April 18, 2012, 07:17:33 PM by W9GB » Logged
G3RZP
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Posts: 4718




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« Reply #9 on: April 19, 2012, 01:06:42 AM »

Most of these cheap devices don't even meet the requirement for operation in 3V/m field strength. That's teh IEC immunity level recommended for light industrial and domestic premises. Hard to believe that will cause ehalth problems, especially when you consider that for over 30 years, some 400,000 people in London lived in that sort of field strength from the TV transmitters. Information from a BBC input paper to the CEPT SE21 group back in 1993.
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WX7G
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Posts: 6134




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« Reply #10 on: April 19, 2012, 02:45:56 AM »

You should run an RF Exposure Evaluation as required by the FCC. To be in compliance it looks like you will have to reduce power to 100 watts or less. That just might solve the RFI problem too. 

Here is a calculator:

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=11352

« Last Edit: April 19, 2012, 02:48:32 AM by WX7G » Logged
VA7CPC
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Posts: 2393




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« Reply #11 on: April 19, 2012, 07:40:12 AM »

With an attic-mounted dipole, at 100 watts, my home alarm system would fire consistently when I transmitted on 40m and 20m and 15m.

Putting ferrite beads on _every wire_ going into the alarm "brain" solved the problem on 20m and 15m.  They would get very warm, dissipating the power that the alarm wiring was picking up.

But I couldn't fix the problem on 40m.  The alarm is now de-powered.

            Charles
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