-----Original Message-----
From: Ian White [mailto:G3SEK@ifwtech.com]
Sent: Tuesday, December 18, 2001 2:59 AM
To: w1rfi@arrl.org
Subject: Re: [RFI] 433 Mhz Wireless Thermometer
Hello Ed
The RFI reflector blocked the following posting for some reason. Please
could you forward it, before it loses all relevance.
Hare,Ed, W1RFI wrote:
>
>Actually, these 433 MHz devices have been "mainstream" for quite some
>time.
>
And in Europe for even longer. It all started with one country allowing
433.92MHz for car keys, and then the pressure was on, because no country
can realistically stop people at its borders because their cars use the
wrong frequency. Very soon, 433.92MHz was all over the European Union,
and made into an official ISM band (see below). Next thing we know, it's
world-wide. Welcome to the global economy.
>These devices are FCC Certificated under Part 15 rules as "periodic
>emitters." The ones I have look at transmit for about 50 milliseconds
>every 30 seconds or so.
You need to keep a strong watch on that, because transmissions in Europe
have gradually crept up from the "one-shot" requirements of car keys to
near-continuous broadcasts of traffic data (an acknowledged mistake in
licensing, but still a precedent for other intensive uses).
>Most operate on 433.92 MHz, a European Industrial, Scientific and
>Medical band. To date, I have no reports of harmful interference to
>Amateur communications from legal devices.
Last Christmas I was horrified when the in-laws in the USA bought my
wife an Oregon Scientific radio-linked thermometer for her outdoor
greenhouse. Horrified, because I operate moonbounce on 432MHz, and this
gadget operates on... you guessed it!
Well, it has worked out fine. With about 50ft separation between the
remote transmitter and my EME array, there is nothing to be heard.
Neither does 1kW on 432.01 interfere with the data link on 433.92.
This doesn't mean that all 433.92MHz modules would be equally good -
there are some very cheap and nasty superregen designs out there - but
it proves that coexistence can be possible.
The real trouble is close to amateur digipeaters and packet nodes using
that frequency intensively. Some car owners find themselves locked out,
and it's a major problem for the breakdown services. Other frequencies
outside the European ham band are also used (the band is narrower than
in the USA) but that means that the interference to car locking systems
comes from police and military services - who are much tougher to deal
with than hams!
--
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
--
73 from Ian G3SEK
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