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Date: Thu, 11 Aug 2011 09:58:03 +0200
From: =?UTF-8?B?U3RlZmFuIFNjaMOkZmVy?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: Re: HB9ASB...
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Hi Gerhard,

I think one has to compare two different situations:

The pole that is on a noisy roof (and its noisy ground) and on the other 
side the pole that is far away in the garden, with its own and clean 
local earth. In the garden a metallic pole should make no difference, as 
you say.

73, Stefan


Am 11.08.2011 05:33, schrieb Gerhard Hickl:
> Roelof!
>
> With interest I was following all the discussions about the "Mini
> Whip"-like antennas.
>
> In your description of the "PA0RDT Mini Whip" you suggest to use a non
> metallic pole for mounting the probe and an (optional) earth-rod to
> ground (sorry Andy!!) the shield.
>
> I might be completely wrong but isn't it the same when one uses a
> grounded metallic pole and connect the shield of the coax on top of this
> pole?
>
> BTW: I have an insulating pole (5m) on top of the roof and yet no
> grounded shielding of the coax but just in the shack. I will connect the
> shield to the lightning protection system at the bottom of the pole and
> see about the difference.
>
> Actually it isn't even a true coax cable but a singe shielded twisted
> pair where the two inner wires are in parallel....Z=? Who knows????
>
> So considering my "fluffy" set-up, I think my VLF grabber is performing
> very well but for sure there is room for improvements as well.
>
>
>
> 73
> OE3GHB
> Gerhard
>
>
>
>
>
>
> Am Mittwoch, den 10.08.2011, 21:26 +0200 schrieb Roelof Bakker:
>    
>> Hello Minto, Stefan,
>>
>> Some food for thoughts:
>>
>> When I tested a mini-whip in the garden with battery feed and also with a
>> battery fed SLM, I found the noise lower than when used inside and
>> operated from the mains.
>>
>> The coax cable from the house station was connected in parallel with the
>> mini-whip by means of a BNC T-piece.
>> The noise increased by 9 dB. My assumption is that this noise is received
>> on the shield of the coax inside the house.
>>
>> Without connecting the shield to a separate radio earth, the noise
>> received on the shield inside the house will travel over the shield all
>> the way to the antenna. There the noise will be received by the sensitive
>> probe. This will be by means of capacitively coupling, I guess. Many
>> people have reported a large drop in local noise by connecting the shield
>> at the bottom of the mast.
>> This also applies to normal active whips of course.
>>
>> 73,
>> Roelof, pa0rdt
>>
>>      
>
>