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Date: Sat, 06 Jul 2013 17:16:38 +0200
From: DK1IS <dk1is@kabelmail.de>
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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>
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Subject: Re: LF: VK1OD's analysis of the MiniWhip antenna
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Status: O

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 an (almost=
)
> static electric field.
> Then it essentially measures the electric field's _potential 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 brought up
> to the mini-whip's electronics either via the metal pole on 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 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 taking the deto=
ur
> 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 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 reaching ou=
t
> to it. I still intend to try to calculate how much this distortion is.
>
> Of course, this whole reasoning breaks down at higher frequencies, wher=
e
> the height of the pole is not small compared to the wavelength; then on=
e
> cannot simply assume anymore that the entire pole is at ground potentia=
l.
>
> 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
>>
>
> .
>