Message-ID: <4E01E9B8.6020001@iup.uni-heidelberg.de>
Date: Wed, 22 Jun 2011 15:10:16 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <000c01cb5a7a$44cfcc50$0401a8c0@xphd97xgq27nyf> <4C1A271605FB0B62@smtp208.alice.it> <op.vjf78o2pyzqh0k@pc-roelof> <4C9A8CC5.30305@gmx.com> <e883a371b121f7efe4940eeacc98be35@xs4all.nl> <4C9B3FCE.5080700@gmx.com> <op.vjhyi5kpyzqh0k@pc-roelof> <AANLkTimay6khcCa2R__C5O3qucRQA6UCFy28Htv38wfC@mail.gmail.com> <7C83B6E4275F422A83872B7E0134B689@Hugh> <op.vxfmdvbhyzqh0k@pc-roelof>
In-Reply-To: <op.vxfmdvbhyzqh0k@pc-roelof>
Subject: Re: LF: PA0RDT polarisation
Content-Type: text/plain; charset=ISO-8859-15; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
X-AOL-SCOLL-URL_COUNT: 0  
x-aol-sid: 3039ac1dc1474e01ec271f0c
X-AOL-IP: 195.171.43.25
X-AOL-SPF: domain : blacksheep.org SPF : none


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