Hi Roelof, I suspect that the differences you see compared with others
depends very greatly on your environment. I think you mentioned a "concrete
wall" This means to me probably reinforced with a considerable amount of
steel rods, possible foil moisture membranes. This kind of structure would
keep signals out and also keep the magnetic interference in. There is no
doubt that moving the antenna away for local noise by even small separations
(near field drops off by the fourth power of distance, I believe) improves
the signal to noise ratio.
Indoor loops do work I get good signals from the States and Canada on a 1.2m
indoor loop. I can often get better S/N than on a large outdoor Marconi.
However I have minimal magnetic interference around my house and it is of
brick construction with no intervening metallic screening. My worst
interference is from next door neighbour's TV, and dimmers. My loop is 6m
away from my PCs which makes a big difference.
What is often not appeciated about voltage probe antennas is that the output
signal voltage is dependent upon the height above ground, and is just the
field strength (say uV /m) multiplied by the effective height (m), which in
your case is the actual height. They can be very disappointing if mounted
near ground level. On the other hand at 17m and away from buildings, they
can be spectacularly good.
Cheers de Alan G3NYK
----- Original Message -----
From: Roelof Bakker <[email protected]>
To: <[email protected]>
Sent: 25 January 2006 14:44
Subject: LF: Re: Re: Mini Whip and local noise
Hello Jim, LF group,
Many thanks for your comments on my local noise report.
>> So one would expect predominantly "magnetic" noise from mains wiring.
<<
That is what I thought as well. However, tests with a battery operated
SPM-3
SLM, showed that local noise on an outdoor E-field antenna is substantial
less than on a magnetic field antenna.
I have also been testing this the other way round: reception of the
carrier
of DCF-39 and semi-local NDB's. Mounting a mini-whip on a bamboo pole and
putting it outside an upstairs window, the signal of DCF-39 increases 22
dB.
Whilst holding a talk for the local ARC in a concrete buiding, the same
test
was performed on 399.5 kHz. The difference was as high as 40 dB. One could
reason that the same attenuation level applies for propagation of indoor
electric fields to the outside world. So far my guess is that this
explains
the low local noise level on my E-field antenna, though it is mounted only
5
metre from the house.
As we all know, magnetic field antennas, e.g. loops, do receive very well
indoors. Thus the same reasoning applies for propagation of local noise in
the magnetic field to the outside world: little if any attenuationa at
all.
It should be nice if someone else could also perform these tests.
Best regards,
Roelof Bakker, pa0rdt
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