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From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <Zen-1HrJrt-0003cc-8z@heisenberg.zen.co.uk>
Date: Fri, 25 May 2007 00:46:04 +0100
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Subject: LF: RE: 500kHz Distance
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Status: O

Dear John, LF Group,

As a simple answer, I would favour sticking with an ERP limit - based on the
present experience the existing 0.1W ERP limit is adequate for a UK-only
band, but if we are looking towards an international 500kHz band, it seems a
bit low if international amateur communications using "conventional" HF-like
techniques are going to be possible on a routine basis over the longer
distances. There doesn't seem to be any problems due to the existing 0.1W
level on 500kHz, and 1W ERP is still very low compared  to other spectrum
users in this frequency range. So if the possibility of an increased ERP
limit exists, I would go for at least 1W ERP, or more if you feel it could
be justified to Ofcom.

A TX output power limit by itself would be OK, provided that power limit was
quite high. But if Ofcom are concerned to limit the maximum field strength
due to amateur transmissions, then they would have to specify low maximum
power to cover the case of an amateur using a relatively efficient antenna
with the "legal limit" TX power. A low TX power would then severely restrict
the possibilities of the band for stations with small antennas and very
limited possibilities for improving them.

Rik's suggestion is quite nice from an amateur's point of view, in that it
gives an "incentive" to produce more efficient antennas, but at the same
time would allow stations who are unable to put up efficient antennas due to
restricted space, etc., still to produce a usable signal by throwing more
power at the antenna. But I think it could be difficult to sell such a
proposal to Ofcom. For the sake of argument, take Rik's figures - in
principle, there is no limit to the ERP that could be obtained with 20W TX
power limit, given gain antennas. Practical large amateur antennas could
give at least several watts ERP with 20W TX power. If Ofcom accept this,
what is the motivation from a regulatory viewpoint for restricting amateurs
with inefficient antennas to 100mW ERP? Why would they care how much power
the transmitter generates, provided the actual amount of power radiated
remains reasonably low?

Cheers, Jim Moritz
73 de M0BMU