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
>