Radiated Power Question


I realize that everyone is going to probably write back and tell me I'm crazy, but this is really driving me crazy, so let me ask, please.

I'm a retired engineer, but have never worked much with RF.

I have been putting up several models of Kidde and First Alert smoke detectors in my new house recently.

Several different models, from both brands, both ionization and photoelectric, some with the 9V battery, some with the built in 10 year Li cell.

All exhibit the same performance:

About once every day or so, at totally random times, they give 3 or 4 Chirps, then nothing for approx another day or so. This is not the indication that it gives for an actual fire; rather from the skimpy instructions they include, an indication of needing a new battery, or some internal fault the circuitry has discovered on its own.

All the batteries are brand new.

Here's what I'm leading up to:

About a quarter of a mile from my house, in a direct line, there's a Ham operator with a massive mast of what must be pushing 100 feet in height. Almost the kind you would see for a small commercial station. Has all sorts of antenna and beams mounted to it. I have no idea what freq's he operates at, and really don't want to ask him.

This is obviously a chap who takes his hobby seriously, and probably radiates at the max allowable power levels, I would guess.

Is there any possibility that if he points his array at my house, it might radiate enough power to cause my problem ?

If not, any thoughts on what else might be causing these chirps from two different mfg's., and several models ?

Much thanks, Bob

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Check the voltage anyway.

What do you mean by "in a direct line"?

Why not? If you approach him in a non-aggressive manner, he would probably be happy to discuss the matter and run tests. When I was operating many years ago, I tried to help out people who thought that I was giving them television interference. I had a number of unreasonable complaints. One was a complaint that I was giving them trouble while I was away on a trip and they couldn't waait to confront me when I returned.

That is a possibility, but I would think it is a long shot. Try contacting the manufacturer or distributer. Contact a local Ham Club. They may have information on such interference

Do these occur simultaneously? Could it be a police car or other mobile source?


-- Fermez le Bush--about two years to go.

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Salmon Egg


Thanks for help.

What I mean is his antenna is line-of-sight to my house, about 1/4 mile away.



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I live in the middle of a National Park. No mobile phone coverage. TV only with the aerial on so high a pole the National Park won't allow it.

Mine chirp. They even chirp during power outages, when the only thing electrical running is battery clocks. My neighbours are sheep. With the odd pony or two. My nearest(human) neighbour is a farmer who doesn't hold with new fangled stuff, like wireless.

They chirp with brand new batteries, too. The mains-powered one chirps (obviously *not* during outages).

They chirp when sat on the workbench. They chirp when stuck on a ceiling

47 foot above the floor.

Doesn't everyone's?

Until you wrote, I thought they were supposed to..

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amateurs are allowed 1 kW or 2 kW peak envelope power on single sideband (SSB).

the gain of a directional antenna can multiply the effective radiated power (ERP)

much of ham operation is done using significantly less power. i.e. 100 watts on HF bands and 10 to 30 watts on vhf and uhf bands.

one reason for large beam antennas is to achieve better received signal strength, and to null out unwanted signals.

i propose a practical test to test your theory. visit your ham neighbor. take the chirping units with you. ask the ham if he would transmit at max power for a bit. see what happens and go from there.

alternatively a small handheld transmitter placed very near the unit will generate a much stronger field then even a very strong signal that is 1/4 mi away.

placing the units in a metal can such as a cake pan may be an option... if you still hear it beep its probably not an RF issue. of course this defeats the smoke detection, its just to test the theory.

if it is an RF issue wrapping the units in a conductive mesh (faraday shield) may help. replacing the detectors with a commercial grade quality may help.

usually when an amateur inadvertently causes interference it is right next door or within 3 houses on a block.

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Yeah, I think they ARE supposed to! :-)

Sure RF interference can get into a lot of stuff and cause problems (I recall one issue of RFI magazine that had this cover depicting a mountain with a radio transmitter on the hillside above the road and a big luxury car smashing through a guardrail and over a cliff! Headline was RFI in electronic brakes! So yeah, it COULD be a problem.

However, in smoke detectors it usually isn't. And if it actually IS due to the Ham radio operator, usually they are very helpful are supposed to do what they can to eliminate the interference that they may cause.

But My guess is that the problem isn't RF. If it were the things would be chirping as if the house were a raging inferno every time the RF was keyed. This isn't happening. The problem is likely more along the lines of random firings of the smell sensor. There are lots of things in the air that can set one off. They are quite generally sensitive to molecules floating through the air in a general way. Also Cosmic rays can trigger them off. The frequency of beeps strongly hints that this could be the source. You aren't going to be able to shield them from cosmic rays. About the only solution is to discover the source of the chemicals triggering them or alternatively get a better design that isn't so sensitive to cosmic rays.

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Thanks all for thoughts on this.

Would just like to re-state that for everyone, that the problem is not the alarms indicating a fire, rather it is a 3 or 4 chirp situation, like a low battery, or a circuitry fault, then nothing for another day or so.


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Ditto. except more like 1-2 chirps, rather than 3-4.

I'd assumed that it was some form of automatic zeroing/ reset that had to be done periodically to set a baseline and to counter drift.

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It's the Dartmoor faeries playing tricks on you!

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