Thu, 09 Jan 2003 09:00:28 -0500
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-------- Original Message --------
Subject: LF: Noise
Date: Thu, 09 Jan 2003 09:44:46 +0000
From: Walter Blanchard <firstname.lastname@example.org>
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!!!
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