Re: KeyFob

[Nigel Orr <nigel.orr@xxxxxxx>]

At 04:40 17/01/00 -0500, you wrote:
>> http://www.dolphin-telecom.co.uk/
if you want more gory details.  If your

And http://www.radiometrix.co.uk/tetra.htm
also has a good description,
about the same things as I said, but put much more clearly ;-)

>One also has to bear in mind that 433MHz is part of the radio amateur
>band. I would guess that there are more radio amateurs than TETRA
stations
>so potentially, there are more sources of interference. Please note
that I
>use the word "interference" loosely. As a radio amateur
myself, I wouldn't
>wish to be classified as such!

I thought it would be 438MHz, but that really _is_ a dim and distant
memory!  Interestingly, in the document referenced below, the point is made
that low power radio devices must not interfere with licensed products, and
it's up to the low power radio designer to make sure that licensed radio
bands don't interfere with them.  In other words, feel free to use the
exempt bands, but don't make a nuisance of yourself!

As for interference, every engineer knows that interference is anything
that _you_ haven't _intentionally_ produced :-)

We have experienced that here, when suffering interference on a 418MHz
link.  We used some directional antennae to triangulate the source, and the
Radiocommunications Agency were very helpful and gave us details of what
the offending source was, but it was licensed, and working within spec- the
fault was simply an inadequately designed receiver module that we had
bought in.

>> It should certainly say MPT1340, the low power approval standard,
but I
>
>Well, on X-10 products, only the frequency is stated and not the usual
>MPT classification.

I can only assume that has been an oversight, although there may be some
odd exemption to an exemption that I haven't heard of...

http://www.radio.gov.uk/document/ra_info/ra114/ra114.htm

at Annex 4 shows the required marking options, which IIRC must be visible
on the exterior of the product.

Actually, the whole document makes interesting reading, if you find that
kind of thing interesting ;-)

Nigel


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