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Author Topic: Amp RF In Burglar Alarm System  (Read 1336 times)
KC8QQH
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Posts: 1




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« on: September 02, 2003, 12:19:49 AM »

I just installed an Icom PW-1 1K Amp, which on transmit sets off my fire alarm circuit of my burglar alarm.  I have disconnected the phone line and no alarm wire are near the antenna system.   The problem has to be RF, but I am matching the antenna at 1:1 with no reverse Power.  Anyone have any thoughts on when the RF is coming in and how to block it?

Bill Bowen
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K7KBN
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Posts: 2802




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« Reply #1 on: September 02, 2003, 12:00:40 PM »

Simply because you're "matching" the amplifier at "1:1" and have no reverse power doesn't mean that your antenna isn't transmitting the signal.  That's what you want it to do, right?

Your antenna doesn't radiate power only in one direction; obviously, your alarm system is picking up some of the transmitted signal (now amplified), and is reacting to it.

Did you have any trouble before you got the amplifier (operating barefoot)?  If not, at what power level does the problem start?  Does the problem occur on all bands, or only certain ones?

You're probably going to have to do some filtering of your system's power leads and sensing leads.  Ferrite beads are generally good chokes.  Not being familiar with your specific case, I have no specific suggestions.
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73
Pat K7KBN
CWO4 USNR Ret.
WA9SVD
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Posts: 2198




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« Reply #2 on: September 03, 2003, 10:08:31 AM »

Simple RF overload due to the proximity of the alarm wiring seems to be the problem.  Filtering the alarm sensors and leads will probably be the only viable solution.
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N9AVY
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Posts: 66




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« Reply #3 on: September 10, 2003, 09:06:05 AM »

If your fire alarm circuit has smoke detectors, you might check to see what type of smoke detectors you have. The two types are photoelectric (low impedence) and ionization (high impedence). A friend of mine who used to work with RF shielded rooms found that the high impedence ionization types were more susceptable to RFI than the photoelectric ones. Ioniztion detectors usually have a little radioactive warning label (not enough radioactive material to be dangerous). Changing detector types may be a solution.

Next step would be to make sure the alarm panel is grounded. Cold water pipe ground should be okay; although in last few year I have found flaky grounds attached to gas pipes and PVC pipes !

If all the above checks out, try adding ferrite beads to fire alarm wires. Occasionally, a .001 uf or .01 capacitor from each wire to ground may help solve the RFI problem. Finally, if none of the above works you may want to try replacing all the fire alarm wire with shielded fire cable - probably a big job with no guarantees. Of course, if this is one of those Radio Shack DIY systems, all bets are off !
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