Hi Tom,
>what´s 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.
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
>-----Original Message-----
>From: [email protected]
>[mailto:[email protected]] On Behalf Of DK1IS
>Sent: Saturday, July 06, 2013 5:17 PM
>To: [email protected]
>Subject: Re: LF: VK1OD's analysis of the MiniWhip antenna
>
>Hello all,
>
>what´s 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 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
>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 out
>> to it. I still intend to try to calculate how much this
>distortion is.
>>
>> Of course, this whole reasoning breaks down at higher
>frequencies, where
>> the height of the pole is not small compared to the
>wavelength; then one
>> cannot simply assume anymore that the entire pole is at
>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
>>>
>>
>> .
>>
>
>
>
>
>
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