Sunday, April 18, 2010

Noise generator

I heard nothing during my attempt last night to receive signals from KP4AO bounced off the moon. Nothing, that is, except a lot of noise. Sitting at the bottom of the garden with my newly constructed hand-held 6 element 70cm beam, the Moon was above and just to the left of the roof of our house. And the nearer I moved the beam to the house, the greater the noise. This house is truly a disaster area for radio reception!

This afternoon I thought I would try to see where the noise was coming from. With the beam horizontally polarized the noise was a broadband hash, white noise, indistinguishable from band noise except that its level is much greater with the beam pointing towards the house. If I turned the beam vertical then the white noise faded out almost to receiver noise, but another pulsing noise came up. It went kerchunk chunk chunk chunk, kerchunk chunk chunk chunk, ad nauseum. And the level of this noise peaked up with the beam pointing right at the shack window!

I switched everything off in the house and it made no impact on the noise whatever. I decided that it must be something battery powered. There is a radio controlled alarm system in the house that has a built-in backup battery. Nothing I can do about that. However I could not hear any noise increase when I went near it with the TH-F7E and a whip antenna. The noise level goes up and down as you walk about the house, as does the kerchunk chunk chunk noise, as if the noise source is invisible.

Eventually I did locate the source of the kerchunk chunk chunk noise. It was coming from an Ascot radio controlled clock sitting on the shelf in the shack just above my radios. I removed the batteries and after a few seconds the noise stopped. I walked about the house some more and in places I heard it again! This sort of thing can make you start to doubt your sanity.

Eventually I found that exactly the same noise was coming from another clock / weather station in our conservatory. It's a different brand, not radio controlled, and (probably not coincidentally) it receives temperature and humidity readings from the same external sensor. Presumably they have some electronics in common and this is transmitting a signal in the 432MHz band.

But I haven't found the source of the broadband hash, which may or may not be related to the crackly S9 noise that plagues most of the HF bands. I think the noise problems at this QTH are beyond solution. I haven't logged an HF band contact from here since 13th March. It isn't that I can't work anything on HF from here, it's just the demoralizing effect of hearing this dreadful noise as soon as you switch on and knowing that there are interesting signals buried under it that I have no chance of hearing.
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