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Author Topic: RFI-Part 1-The alarm system  (Read 582 times)
KC0ITT
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Posts: 10




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« on: May 27, 2001, 12:14:24 AM »

I am having lots of fun using my new HF capabilites, but run into a bit of a snag.  When I transmit on 40 or 15 meters, I often inadvertently set off our alarm system.  Specifically, it set of the fire alarm.  Then I get a call from the central monitoring company asking me if we need a fire truck sent to the home!

Needless to say, this causes considerable operating difficulty.

What is the best way to tackle this problem?  I was thinking of winding the wires from the smoke detectors around some ferite cores.  Are there other suggestions?

Thanks,

Mike
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RobertKoernerExAE7G
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Posts: 1435




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« Reply #1 on: May 27, 2001, 04:35:31 AM »

Hi Mike

You will probably get the most help if you indicate what your station set up is.

Glad to see you think CW is fun.

Have FUN
Bob
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N8FVJ
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Posts: 692




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« Reply #2 on: May 27, 2001, 07:53:51 AM »

In addition to the ferrite chokes, install a .01 ceramic cap to all inputs at the alarm main circuit board. A .01 capacitor may have to be installed on both ends of the 'field' device. If the system is wireless, you may have to replace the system with a 'hard wire' type. I fixed my TVI and telephone RFI problems with .01 capacitors. When I replaced my older Icom IC-728 transceiver with a newer generation transceiver using mos-fet finals, the RFI problems came back. The RFI was not as serious as before, but present. I replaced my newer transceiver with an Icom IC-729 which has exceptional xmit specifications. The RFI problems went away. I do not understand why poor in-band xmit IMD specs would cause RFI, but I will not have a 'dirty' transmitter in my radio room. The new Yaesu FT-1000 Mark V operating at 75 watts class A is extremely clean with regard to xmit specs. This may be my next transceiver as the IC-729 is rather limited in performance.
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KC0ITT
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Posts: 10




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« Reply #3 on: May 27, 2001, 09:27:27 AM »

The setup that gives me trouble is using an ICOM IC-735 connected through and MFJ 962C tuner feeding ladderline to my 135' OCF Dipole.  

The Dipole runs across the top of the house.  

Thanks,

Mike
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N8FVJ
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Posts: 692




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« Reply #4 on: May 27, 2001, 09:42:28 AM »

The IC-735 has a clean transmitter, 3rd order harmonic is an outstanding -65 db down and 3rd order IMD is -33. Throw out my 'dirty' transmitter problem I had at my QTH. Jim
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W4CNG
Member

Posts: 177




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« Reply #5 on: May 27, 2001, 10:36:08 AM »

I too had the same problem except I have attic mounted dipole antennas following an 800watt amplifier.  I disconnected the 2nd floor smoke detector, (yes I have 2 detectors on each level of the house 1 for the inspectors, and 1 for the Alarm monitoring on each of the 3 levels of the house). It was RFI into the Electronics of the smoke detector.  I choked it, bypassed it, everything, disconnection worked, and I still have a comfort level in the house.  I replaced it with a rate of rise Heat detector in the attic.  This unit has NO electronics and is a one time trip device in the event of Hi-Temp rising fast in a protected area.
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AC5UP
Member

Posts: 3875




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« Reply #6 on: May 28, 2001, 08:51:19 AM »

Uhhhhhhhhhh... I think I may have an answer for you.

I'm also running an off-center fed dipole, but I'm feeding it with a 4:1 dual core Guanella balun at the feed point and 50 ohm coax back to the rig. A good 50' of this coax runs along the ground and I have no problems with RF in the shack, phone, or other devices. Between the balun and the close proximity of the coax to ground, the chance of RF on the braid is nil.

The antenna is a no-tune natural match on all bands except 75/80 meters where it needs a little help from the ATU in the IC-756. The antenna does NOT work on 160, 30 or 15 Meters. It's not supposed to. My SWR on 15 Meters approaches infinity despite near-zero readings elsewhere. If you're forcing a pseudo-resonance on 15 Meters through the tuner, it doesn't surprise me that you're having RFI problems.

A tuner and ladder line won't "fix" a non resonant wire, and my OCFD has literally Worked The World everywhere _except_ 160, 30 and 15M. As an FYI, read through the RFI problems found here and you'll usually find the words "antenna tuner" somewhere in the description. A tuner can help tune an antenna that's almost resonant or needs an oddball impedance match, but there is no magic in the box...
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