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Author Topic: RFI problem with Brinks/ADT alarm system solved.  (Read 3601 times)
K0UA
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Posts: 1380




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« on: September 19, 2017, 06:22:59 PM »

I have had a problem for some time with RF on 80 meters getting into the alarm system and causing a problem where it could not communicate with the annunciator. As that is what the alarm code indicated.  Of course it would call the central station, and report this. 100 watts of SSB would not do it, 100 watts of CW would not seem to do it either.  This is because the duty cycle of these modes is lower than digital modes.  But anything over about 35 watts of digital key down 100 percent duty cycle would set it off.   Been that way for many years. I decided to fix it and ordered 18 of these from Amazon.

Put them on the bundle wires going into the steel control box.  I had to break them into two groups as the ferrites would not go around them as a single bundle. But it sure worked.  I can do 100 watts key down FT8 now. No problem.

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K0UA
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« Reply #1 on: September 29, 2017, 09:38:26 AM »

Actually not entirely solved.  Seems that the FT8 frequency of 3574Khz is fine but 100 watts on the RTTY frequency of 3593, is still a problem.. Who would of "thunk" it?  That less than 20 Khz makes all the difference in the world. But it does. The addition of more ferrites has not really helped. Cutting back to 75 watts seems to not trip it.  Who would think 25 watts would make that much difference.  We must be on the "ragged edge".  Isn't RFI fun?
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K0UA
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« Reply #2 on: September 29, 2017, 02:11:21 PM »

And bonding the lid to the box (steel box and lid) and grounding the box to the electrical statement ground hasn't helped either. OK I have some .01 and some .1 disk ceramics coming. Perhaps bypassing some of the lines will help.
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K0UA
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« Reply #3 on: October 02, 2017, 09:25:49 AM »

Still waiting in the bypass caps to come in. Slow boat and all.  Any other suggestions? Thanks.
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WB4SPT
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« Reply #4 on: October 08, 2017, 08:52:25 AM »

Is the alarm system sensors wired or wireless?   I have no idea what those ferrites are for material or characteristics.  Is there a spec? 
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K0UA
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Posts: 1380




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« Reply #5 on: October 08, 2017, 11:18:07 AM »

Is the alarm system sensors wired or wireless?   I have no idea what those ferrites are for material or characteristics.  Is there a spec?  

Everything is wired.. AND wired with "crap" wire.  The old non or very slow twisted 4 conductor phone wire we used to call JKT.  it is considered CAT1 wire.  Real junk.

I am also not sure what the mix is on those ferrites.. But after the second round of application of them I can now run 100 watts on the FT8 frequency, but if I go up just 20 khz in frequency I can't run more than about 70 watts without tripping it off.   My next attack will be in the bypass capacitor arena.  As soon as they get here.
Obviously the ferrites helped, and helped a great deal, but it was not a total solution.
« Last Edit: October 08, 2017, 11:23:34 AM by K0UA » Logged
WB4SPT
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« Reply #6 on: October 08, 2017, 11:33:28 AM »

OK,  i'll bet some strategically placed .1 or .047uF caps will work wonders. 
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K0UA
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« Reply #7 on: October 14, 2017, 11:49:16 AM »

OK,  i'll bet some strategically placed .1 or .047uF caps will work wonders. 

That would be a good bet.

 The .01 disc ceramics did nothing to help.  BUT the .1  sure seemed to fix me up.  I used 3 of them.  across the 16 volt AC supply and across the auxiliary DC voltage that seems to be common to every sensor and one from the listed alarm that it could not communicate with the announcer to the negative of the DC supply.  I ran 100 watts (which is all the rig can do) of RTTY for over 2 minutes on the frequencies on 80 where I had the problem yesterday before adding the caps and it was quiet as a mouse.

 SO.  it 'looks' like I have it solved. I found it strange that with the ferrites I could operate on 3573, but move up to 3593 and as I found out all the way to about 3730, and any key down mode like RTTY would set it to beeping and calling calling out to report a trouble alarm.  Which then elicited a call in from the alarm company saying there was trouble in the system, and suggesting I run the self test. An intermittent low duty cycle mode like SSB did not set it off.

Bottom line.  The ferrites helped but didn't completely fix it on all 80 meter frequencies. I spent $30 on them.  Less than a dimes worth of .1 caps
 from China which finally arrived on the slow boat Smiley seems to have me fixed up.  80 meter RTTY contest here I come!
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