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Message-ID: <5.1.0.14.0.20030324122153.00abb360@gemini.herts.ac.uk>
Date: Mon, 24 Mar 2003 13:42:21 +0000
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
In-reply-to: <000601c2f033$e413b3d0$d6e136d2@bob2l2u6k2n1g3>
References: <5.1.0.14.0.20030320183946.0260e158@gemini.herts.ac.uk>
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Subject: Re: LF: Selection of spot frequencies for DX
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Dear LF Group,

At 17:09 22/03/2003 +1200, Bob wrote:
>So my suggestion for selecting frequencies for long haul DX between amateur
>stations is to avoid multiples of 50 or 60 Hz (50 Hz mains being used in
>some regions, 60 Hz in others).  137.7100 kHz is an example of being clear
>of 50 Hz harmonics, whereas 137.7000 kHz is dicing with the 2754th harmonic
>of 50 Hz, plus or minus some tolerance for the national grid.

Not sure about ZL, but here in the UK the 50Hz nominal mains frequency 
drifts around quite a bit - perhaps a few tenths of 1%. Seen on a fairly 
coarse resolution spectrogram, the harmonics give a series of wavy lines 
spaced by 50 or 100Hz, which drift enough to give overlapping coverage 
during a period of a few minutes. But with very narrow resolution 
spectrograms, this just adds to the "wide band" noise level, rather than 
producing well-defined spectral lines, because the frequency does not 
remain within one FFT box for long enough to produce a line. Most of the 
stable spectral lines on LF at my QTH seem to be Loran, but a significant 
number are not. I also see a very faint line at 137.700kHz sometimes - 
wherever it comes from, it must be crystal controlled to have sufficient 
stability.

Cheers, Jim Moritz
73 de M0BMU