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Date: Fri, 25 Jun 1999 09:45:04 +0100
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To: rsgb_lf_group@blacksheep.org
From: drassew2@interalpha.co.uk
Subject: Re: LF: Noise from phone lines
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Reply-To: rsgb_lf_group@blacksheep.org
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I am a member of the Expert Group put together, predominantly by the RSGB,
to look at the issue of Power Line Telecommunications.  The results of our
findings hvae been well reported in the EMC columns of RadCom recently, and
these are being formulated into a specification to be issued by the
RadioCommunications agency on radiation levels from ALL fixed wiring in the
150kHz to 30 MHz band.  Dave Lauder the editor of that column is a member of
the Group.

This reflector is not the forum to give out details of this specification,
as it is still in the consultation stage with industry and users, but if
approved it is safe to say that radiation levels will be specified at a
level sufficient to not cause interference to LF - HF communication at a
distance of 10m from any fixed wiring - not specifically power lines.  That
is not to say some systems may not be compliant, but if interference is
caused there will be a legally enforceable specification in place.

As for the PLT issue - and this was reported in the EMC columns - the
amateur bands have never been under a serious threat from PLT as the
proponents were at great pains to protect the services they knew about such
as amateurs, broadcast, distress.  Unfortunately, the frequencies they
unilaterally decided were 'safe' to use happened to be where my professional
interests lay and hence my concern with the matter - the amateur radio
conncetion was coincidental and convenient!

I suggest you re-read the RadCom EMC columns over the last year or so for a
full update.  Unfortunately the frequencies of interest do not extend down
to 137kHz - there is a valid reason for that, and is probably explained in
one of the RadCom articles.

Andy Talbot  G4JNT


>>From G3YMC

>An associated topic, not yet having hit us in the UK yet, but imminent, is
>the ADSL system for putting high speed internet at 1.5Mb/s down normal
>telephone lines. An excellent, though fairly technical, article on this and
>associated techniques appears in the IEE Electronics and Communications
>Engineering Journal, June 1999 issue, entitled 'High Speed Copper Access: a
>tutorial overview'.
>
>The article in particular discusses interference problems, to and from,
>amateur transmissions, and indicates that the designers do indeed take
>these interference problems seriously.  Unfortunately they have not heard
>of 136kHz and state that amateur interference is not an issue with ADSL
>which only uses frequencies up to 1MHz or so!  Some of the scenarios
>considered for the much faster (26Mb/s) VDSL system which is much further
>down the line for deployment however make me think that we will have big
>problems if these systems take off!
>
>I have not seen such open discussion of amateur matters in any official
>papers from the proponents of the PLT (data over mains) systems, which as
>we know have been shown to have serious QRM problems for the amateur bands.
>I wonder if the two parties do talk to each other!!