Hello Roelof,
Yes, the noise that is picked up in the house will travel to the miniwhip,
that is also my experience. (But now I am a bit confused how it then gets
back to the RX, by capacitive coupling to the e-probe or because the coax IS
the antenna, or both. Have to think harder)
Just as a test I created a choke in the coax, somewhere in the garden (wound
some of the coax over a largish ferrite rod – will measure the achieved
inductance later). The QRM from my Alinco SMPS when tested was noticeably
lower, even though I did not ‘Ground’ (sorry Andy) the coax.
Regards,
Minto pa3bca
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Ceterum censeo Carthaginem delendam esse
-----Original Message-----
From: Roelof Bakker
Sent: Wednesday, August 10, 2011 21:26
To: [email protected]
Subject: Re: LF: Re: HB9ASB...
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
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