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Dear John, LF group,

This is a CW carrier that has been present on 136.645 or thereabouts for as long as I have been listening on LF from my present QTH. It is of the order of several uV/m, so quite strong when the band is quiet, and often makes it difficult to copy CW stations here. It is just a carrier, with no modulation I can detect, and I have never known it to be QRT.

I D/F’d it a few years ago to a 400kV overhead power line that runs from a switching yard near Aldenham, Watford, just beside the M1 motorway, to another switching yard north of Luton, also beside the M1. The signal strength increases very rapidly under the lines, so I guess the signal is transmitted differentially between two or more of the conductors, and the radiated carrier is just “leakage” from the transmission line caused by imbalance of one kind or another.

I believe the range 9kHz to 148.5kHz is used in Europe for power line signaling - If you want to find out whether a particular power line is carrying a similar signal, I would recommend going /P and getting as close up to the power line as possible – the high signal strength will then make it relatively easy to differentiate between power line signals and the other noises one hears on LF. It should be fairly easy to follow the route of the cable, and see if the noise is associated with it at several places – LF noise seems to propagate for a long way down most kinds of cable.

Cheers, Jim Moritz

73 de M0BMU

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of John W Gould
Sent: 18 July 2005 12:04
To: rsgb_lf_group@blacksheep.org
Subject: LF: Watford Whistle

Apart from the interesting account of the nulling experiment, below, I was intrigued by the mention of the "Watford Whistle" - grateful if Jim or others could elaborate on this or known power-line transmission systems used here in the UK. On occasions I have a huge amount to 100Hz related QRN, which I can put down to power-line QRM (I have an underground power cable running across my garden somewhere) or the proverbial switch mode PSUs.

73 John, G3WKL