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From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
References: <CAKvcm2dpuftdtK6OdQv8fOfiw+4yQrPBQBHJ-FN2gDbT4P_oMQ@mail.gmail.com> <51D498BD.3050007@iup.uni-heidelberg.de> <op.wzq2tgvnyzqh0k@pc-roelof> <005b01ce798a$b0476600$6d01a8c0@DELL4> <op.wzrfpjyyyzqh0k@pc-roelof> <20130706131640.GG5246@cs.utwente.nl> <51D834D6.9050403@kabelmail.de>
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Date: Sat, 6 Jul 2013 18:14:15 +0200
Message-ID: <8C9E7EDCA83145B4B00E1D951DC401B1@Clemens0811>
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Subject: RE: LF: VK1OD's analysis of the MiniWhip antenna
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Status: O

 Hi Tom,

>what=B4s about two mini-whips mounted back to back?

That's exactly what I was going to propose but you have been quicker. =
:-)
Take two miniwhips to form a dipole,feed it balanced by a proper =
balancing
device
and see what happens.=20
We've done this with the "Microvert" years ago and it was a real eye =
opener.
I would second Jays argument that it is virtually impossible to isolate =
the
feedline
effectively from the E-probe.

73
Clemens
DL4RAJ=20


=20

>-----Original Message-----
>From: owner-rsgb_lf_group@blacksheep.org=20
>[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of DK1IS
>Sent: Saturday, July 06, 2013 5:17 PM
>To: rsgb_lf_group@blacksheep.org
>Subject: Re: LF: VK1OD's analysis of the MiniWhip antenna
>
>Hello all,
>
>what=B4s about two mini-whips mounted back to back?
>
>73,
>Tom, DK1IS
>www.qrz.com/db/dk1is
>
>
>Am 06.07.2013 15:16, schrieb Pieter-Tjerk de Boer:
>> Hello all,
>>
>> I tend to think about the mini-whip on LF and MF in terms of=20
>an (almost)
>> static electric field.
>> Then it essentially measures the electric field's _potential=20
>difference_
>> between a point somewhere up in the air, namely where the mini-whip's
>> metal plate is located, and ground. The ground reference is=20
>brought up
>> to the mini-whip's electronics either via the metal pole on=20
>which it is
>> mounted, or (the outside of) the coaxial cable.
>>
>> This explains Roelof's observation (see below) that it doesn't matter
>> whether he mounts the mini-whip on a vertical pole, or on a=20
>horizontal
>> pole out of a window (but in the same position).
>> In both cases, it measures the same potential difference, although in
>> the latter case the ground connection is longer, namely=20
>taking the detour
>> via the horizontal pole and whatever is inside the house. Presumably,
>> Roelof's house is small compared to the 399.5 kHz wavelength, so this
>> detour shouldn't matter.
>>
>> This view also at least approximately matches VK1OD's NEC4=20
>calculation,
>> in the sense that he finds an output voltage which is of the order of
>> the field strength times the antenna height.
>>
>> A weak point in this reasoning is the fact that since the entire pole
>> (or outside of the coaxial cable) is at ground potential, it distorts
>> the electric field around it. So the mini-whip's plate is not at the
>> same potential as it would be without the ground connection=20
>reaching out
>> to it. I still intend to try to calculate how much this=20
>distortion is.
>>
>> Of course, this whole reasoning breaks down at higher=20
>frequencies, where
>> the height of the pole is not small compared to the=20
>wavelength; then one
>> cannot simply assume anymore that the entire pole is at=20
>ground potential.
>>
>> 73, Pieter-Tjerk, PA3FWM
>>
>>
>> On Fri, Jul 05, 2013 at 07:47:33PM +0200, Roelof Bakker wrote:
>>> Hello Jay,
>>>
>>>
>>> I don't think so.
>>>
>>> I have carried out a test with a vertical feed line and a horizontal
>>> feed line on a pole pushed out an upstairs windows. In both cases
>>> the antenna was in the same position and showed equal signal levels
>>> from the groundwave of ONO-399.5 at 59 km.
>>>
>>> 73,
>>> Roelof, pa0rdt
>>>
>>
>> .
>>
>
>
>
>
>
>-----
>E-Mail ist virenfrei.
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>Version: 2013.0.3345 / Virendatenbank: 3204/6469 -=20
>Ausgabedatum: 06.07.2013=20
>
>