From: "James Moritz" <J.R.Moritz@herts.ac.uk>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 14 Jan 2004 14:54:17 -0000
Organization: University of Hertfordshire
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Subject: LF: RE: lf and noise and offshore.
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Dear Dick, Peter, LF Group,

I am currently running 1200W at 136kHz into about 50m of wire antenna in
a residential area and, like the others, I do not experience significant
problems with QRM to domestic equipment caused by the LF signal. The
exception to this is when corona breakdown of the antenna is occurring,
when I get "hiss" and crackling sounds on FM broadcast, and "snow" on
UHF TV reception - it gives quite a useful warning!

The main problem most LF amateurs have is the other way round - QRM to
LF reception caused by noisy domestic electrical equipment, which varies
from mild annoyance to making reception of amateur signals completely
impossible. The noise propagates long distances down the mains wiring. I
have to use loop antennas at the far end of my garden to get away from
the noise produced by the mains wiring in the neighbourhood. I bet it
would be much better on a ship...

PE1ECM wrote:
>Does it make sense when I try to start LF from my ship  /MM ( steel
>fishermen cutter ) instead of from my condo ?
>Does sea again ( if any at all ? ) and low man made en evironment
noise >add
>substantially to the LF performance ?
>( Besides, on my vessel I could erect bigger aerials than at the home
QTH >).

>Where could I find explanations on (possible ) sea gain on LF ?
>Where could I find information on the ( LF ) noise levels offshore ?

I don't remember anyone operating /MM on LF before. There seems to be
almost no info around about LF marine operation - people seem to have
stopped doing that after WW2. It would certainly be interesting to try
it. Most of the losses in LF antennas is due in one way or another to
the ground and objects surrounding the antenna. This leads  to very low
antenna efficiency (usually <0.1%) for most amateur antennas. Since the
ground is salt water and the structure of the ship is metal, losses
should be much lower for a ship antenna than land-based amateur LF
stations. It would be very interesting to find out if this is really
true. As far as received QRM goes, it only takes one little noisy
electronic device to spoil LF reception - but, unlike the normal
situation, since all such equipment would be part of the ship and under
your control, so it should be possible for you to switch
off/filter/replace any  noise sources that you find on board. Once you
had done that, a ship that is some distance offshore should be an ideal
LF receiving site.

Cheers, Jim Moritz
73 de M0BMU