Message-ID: <5.1.0.14.2.20030109085759.00a04cd0@mail.pncl.co.uk>
Date: Thu, 09 Jan 2003 09:44:46 +0000
To: rsgb_lf_group@blacksheep.org
From: "Walter Blanchard" <blanch@pncl.co.uk>
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Subject: LF: Noise
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Re the 520/1010 discussion.  Wilsons' main objection to the 520 appears to 
be that it suffers from a great deal of local noise pickup, which actually 
would be expected from ANY vertically-polarised E-field antenna. An H-field 
antenna; e.g. a loop, does not so suffer but this is a fundamental physical 
fact and should not be attributed to the 520 as if it were something wrong 
with that antenna itself. These little active verticals are very handy for 
restricted spaces; e.g. on boats, where there simply isn't the space to put 
up a loop; but mounting them on a grounded metal mast is ESSENTIAL - if 
they're put up on a fibreglass pole they will have far less pickup.  I had 
one on my boat top of the mast and it could pick up 10w 300 kHz DGPS 
stations 800 kms away in daylight  - no local noise there, of course (at 
least, when the engine was off!).

Apart from that, can anyone tell me why local noise IS a 
vertically-polarised E-field problem? I can intuitively (I think) 
understand that it would be E-field since it is primarily a high-impedance 
phenomenon; but why VERTICALLY-polarised? If it's radiated from local house 
wiring etc surely it should be randomly-polarised and just as evident on 
horizontally-polarised antennas? I have a 30 m vertical I occasionally use 
on 80m and a horizontal dipole for 80m near it. VERY often there is so much 
noise on the vertical I can't even hear my local net; on the horizontal at 
the same time there is only the faintest trace of noise and everyone is 
easily audible.  Same on 160m. All the texbooks agree local noise is 
vertically-polarised but not one of them explains why.

Incidentally for 80m reception my horizontal dipole out-performs not only 
the vertical but also a 1m dia loop quite easily both in terms of s/n ratio 
and absolute pickup. I suspect the same would be true of 136 kHz if anyone 
ever had the space to put up a 136 kHz horizontal dipole at a reasonable 
height!  Now THERE's a challenge for G3KEV.

And a Happy New Year to all!!!

Walter G3JKV.


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