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Re: [RFI] Weather Station on 433.92?

To: rfi@contesting.com
Subject: Re: [RFI] Weather Station on 433.92?
From: Ian White GM3SEK <gm3sek@ifwtech.co.uk>
Reply-to: Ian White GM3SEK <gm3sek@ifwtech.co.uk>
Date: Thu, 12 Apr 2007 08:31:16 +0100
List-post: <mailto:rfi@contesting.com>
>The good news is that 433.92 MHz is not real close to the weak signal 
>calling frequency of 432.100 MHz, which I (and others) use.  I have two 
>different brands of wireless digi thermometers in use at my QTH, both 
>are of the type operating at 433.92 MHz, and neither seems to interfere 
>with the other, nor have I had any problems with those senders QRMing 
>my 432 receiver.  Better yet, my 100 watts on 432 xmit does not seem to 
>crunch the receivers, one of which is in the ham shack (as part of a 
>WWVB-controlled clock).  I have yet to see any artifacts on the display 
>while I operate in the band.
>As always, YMMV.  FWIW:  When I first heard about these gadgets 
>operating in the 70cm band, I was pretty upset and feared the worst. So 
>far, no issues at my place and yes, W1RFI and the League are well aware 
>of these systems.

I was able to operate EME on 432MHz with an Oregon Scientific wireless 
thermometer transmitting on 433.92, less than 50ft away from the 
antenna. The remote sensor only transmits in bursts, but down at the 
bottom of the band I couldn't detect a thing. Also there was no 
detectable radiation from the receiver, which is more important because 
the RX is active all of the time.

1kW from my TX might have affected the receiver in the base station, but 
there was no way to tell because that particular system wouldn't have 
cared about missing an occasional update.

Blocking of the RX can be a problem with remote alarms, because some 
alarm controllers are programmed to interpret a blocked RX as a 
deliberate attack. Hopefully the alarm industry is beginning to learn 
how stupid that is. As 433.92MHz continues to fill up, all around the 
world, the most likely source of QRM is not the amateur down the road, 
but other wireless gadgets in the same household.


73 from Ian GM3SEK
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