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Re: LF: PA0RDT polarisation

To: <[email protected]>
Subject: Re: LF: PA0RDT polarisation
From: "Hugh_m0wye" <[email protected]>
Date: Thu, 23 Jun 2011 10:30:49 +0100
References: <000c01cb5a7a$44cfcc50$0401a8c0@xphd97xgq27nyf> <[email protected]> <op.vjf78o2pyzqh0k@pc-roelof> <[email protected]> <[email protected]> <[email protected]> <op.vjhyi5kpyzqh0k@pc-roelof> <[email protected]> <7C83B6E4275F422A83872B7E0134B689@Hugh> <op.vxfmdvbhyzqh0k@pc-roelof> <[email protected]>
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Thankyou very much to those who answered my questions.
When I have used an E-field probe to explore unwanted radiation from circuit boards, the orientation of the probe had an effect on the signal strength. But now I can see that on this larger scale, the plate of the probe will generally be above the counterpoise, so vertically polarised signals will always be favoured, whatever the orientation of the probe.
I feel I have a better understanding of how it works now.
thanks once again.
73, Hugh M0WYE
----- Original Message -----
Sent: Wednesday, June 22, 2011 2:10 PM
Subject: Re: LF: PA0RDT polarisation

Hello Hugh,

The model i have in my mind is a capacitive divider that is within an E
field (TX signals and noise). There are 2 plates, the probe and the
counterpoise. The counterpoise has a C against ground that is several
orders higher as the probe, normally. If the antenna is in a fixed
position, you may vary the way the feed cable runs, and change its
capacity against ground from say 1 nF to 2 nF. But the plate has just
about 3 pF and so the voltage across the gate and source of the amp
input does not change significantly.
However, if you place the probe near a tree or a high building, the
signal usually drops significantly, since the E fields becomes much
lower near lossy and conductive things. So this directly affects the
input voltage and thus mostly the SNR.
Rising the antenna much above ground is usually useful. But if you would
be outside in a flat landscape without trees and local noise, is would
be totally appropriate to put it on the roof of a car.
Good luck with your works. What do you plan? :-)


73, Stefan/DK7FC


Am 21.06.2011 17:23, schrieb Roelof Bakker:
> Hello Hugh,
>
> Though it may not make sense, mounting orientation is irrelevant.
> And the feed line does not need to run vertical either.
>
> I have tested the antenna at the same "position in space" with two
> ways of mounting.
> The first one was the normal way with a vertical mast in the garden.
> The second way was using the same mast and cable length, but this time
> extended horizontal from an upstairs window.
> The receiver was a battery operated selective level meter, which could
> be read to 0.5 dB.
>
> The test was carried out receiving the vertical polarized signal of
> NDB ONO on 399.5 kHz, 59 km away.
> The measured levels agreed within 1 dB!
>
> So the good news is when the need arises, the antenna can be mounted
> on a pole and pushed out of the window!
>
> Best regards,
> Roelof Bakker, pa0rdt
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