The AM Forum

We have three Kidde AC/battery-backup, linked smoke & CO detectors in the house. They always give me an S9+20 report when I load the Valiant on 75M. My assumption was the Valiant or cabling to it was the problem because I never had the issue anywhere else. This afternoon, out of idle curiosity, I brought up the newer rig (Kenwood TS-480-SAT) and ACOM 1011 amp up on 75M. BEEP - BEEP - BEEP - FIRE - FIRE - FIRE! The Valiant is blameless, obviously.

It could be the inter-detector wiring is resonant on 75M, or my horrible grounding or both. I went to Home Depot and bought three new (and expensive) smoke/CO detectors with 10-year lithium batteries this afternoon thinking I could just mount them on the old ceiling mounting plates. Of course, that won't work because they completely changed the mounting system. Another idea then struck me. I disconnected the interconnect wire from 2 of the 3 detectors. Loaded up to full power on 75M and no alarms!

There really isn't enough slack to put toroids on the interconnect wire so I may just leave them independent and not worry about it.

It it's just the interconnect, you might be able to put a cap from the interconnect to the neutral at each detector.  This may clear up the problem.  Probably not a good idea to leave the detectors independent of each other.  At least in my house, a detector going off in the basement would not be heard on the 2nd floor.

You may need to make up chokes with separate wire, then patch them into the existing wire.

I agree.  Get some toroidal cores and make a common / differential mode filter with the right material mix for the frequency involved and then put some .01's line to line across the device side of the filter.  The high series inductance of the filter in conjunction with the bypass caps should nail the problem.  Keep the filter as close as possible to the device.  

Before you do anything, remove right at the device the AC feed allowing it to run on its internal batteries.  That will give you an indication if its coming in the AC feed or the interconnect control wiring.  My guess its not the AC, but in the control cable.   Still, its prudent to do the test so you partition the problem.  

Joe - GMS  

The classic from Curb Your Enthusiasm

http://www.youtube.com/watch?v=bZCEvVBY4LI

Great scene. I needed a chuckle!

I wimped out. There is absolutely zero slack in the signal wire and all three detectors are mounted in ceiling boxes. I could open the ceiling up and add chokes but took the hopefully easy way out. The Internet came up with a very good price on First Alert Smoke/CO combination detectors that are battery operated and RF linked for alarms  http://www.smokealert.net/ProductDetails.asp?ProductCode=0W-Q10T-D9EG

The old ones work fine except when I'm on 75M, even with the signal line off. As Steve pointed out, we would never hear the basement alarm on the upper level. The basement is where all of the HVAC stuff, water heater, etc. live.

Thanks to all for the comments. I'll follow up with a report on the RF linked alarms when they arrive

73
Jack

The First Alert detectors are in, connected by RF and work. 75M is now on  my approved frequency list. Will try to make the AM net on 75 later this morning.

By the way - these things are extremely loud!

Interconnect smoke detectors are here at the QTH.  We an episode with one of them going off at 2AM briefly for a few days almost like clockwork. Couldn't figure out why but it was one detector in the office. It would sound off first before setting off the whole system.  The last time it went off I ripped from the ceiling and tossed it in the garage.  A couple of days later I took a look at it and blew into it to blow out dust and reconnected it. A night later and off it goes again. So down it comes again.  Hit it with compressed air this time and out comes this tiny little spider smaller than a BB.  It met it's maker with my index finger.  It's been fine ever since.

Poor little spider, he didn't know.

When I did antenna installs, I would almost always find a little white spider living between the mast and the bracket high up at the roof.  I could never figure out what the hell they were doing up there.  I think, IIRC even in the winter I might find one.

I just moved him out of the way and continued to remove the old antenna.

Some sort of antenna spider, I guess.

Fred

I assume you were running a cubilcal quad  ::)