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Message-ID: <C69BBA94D0A240C49322934E999B00CA@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <008f01caf784$779a11d0$0301a8c0@your91hoehfy9g> <Pine.LNX.4.64.1005192058370.18919@paranoid.lipkowski.org>
In-Reply-To: <Pine.LNX.4.64.1005192058370.18919@paranoid.lipkowski.org>
Date: Wed, 19 May 2010 21:06:44 +0100
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Subject: Re: LF: Alpha dashes
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Dear Mal, Jacek, LF Group,

For a detailed and accurate picture of signal and noise levels at VLF in the 
UK (and a fair amount of LF too...), go to Paul Nicholson's site at 
http://abelian.org/vlf/spectrum.shtml, which shows this information updated 
in nearly real time. There are links to other VLF web sites, and streaming 
audio too.

SQ5BPF wrote:
> unfortunately they are down now, so i can't tell you what is the s/n now. 
> but it's hard not to receive these stations. with an e-field antenna (or 
> with a h-field antenna but at some distance from powerlines) you can hear 
> them without any downconversion, provided that your headphones (and ears 
> :) have high enough frequency cutoff. with downconversion to 800Hz i would 
> give it 599 if it were cw (actually they sometimes transmit a marker in 
> cw)
>

I guess Alpha is a few dBs weaker in the UK. But I have usually been able to 
receive the Alpha beacons with my "Electromechanical Receiver" 
(http://www.wireless.org.uk/mechrx.htm), using a 10m high inverted L 
antenna, when I have had that RX set up for an SAQ broadcast - the 
motor/generator spindle speed has to be reduced for the lower alpha 
frequencies of course. The electromechanical RX is completely passive, and 
the saturating-core mixer is not very efficient, so it has about 20dB power 
loss between antenna and headphones, but even so, the QRN at VLF is so 
strong that this external noise is the limiting factor on receiver 
sensitivity, even one which has no electronics...

Cheers, Jim Moritz
73 de M0BMU