My question goes to the practical. Say we are using some version of RG8U;
isn't it better to choke the feedline at both ends? And what are the cheapest
but best toroids or beads to use? Where do you get them? --Brent N9HZ
ps was working 10m AM yesterday with the Orion, got great audio reports.
From: Jim Brown K9YC <k9yc@audiosystemsgroup.com>
Date: 2008/06/07 Sat AM 01:29:28 CDT
To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] OT: coax versus parallel wire, insulated wire for
aerial
On Fri, 06 Jun 2008 23:03:34 -0600, Dr. Gerald N. Johnson wrote:
>A balanced line, if perfectly balanced and closely spaced should have
>little pickup, but the well shielded coax line with the current balun
>at the antenna should pick up less on the feed line.
A clarification. Noise is picked up on ANY transmission line as a common mode
current, and is coupled to the antenna if the antenna itself is unbalanced.
The vast majority of REAL ham antennas have some degree of imbalance due to
their interaction with surroundings.
Common mode current can be effectively killed by coaxial chokes on lossy
toroids. It is quite difficult to build an equally effective choke for
balanced lines. The reasons are spelled out in my tutorial.
http://audiosystemsgroup.com/RFI-Ham.pdf
THIS is why antennas fed by open wire line tend to be noisier than those fed
with coax. It isn't the line, it's the fact that you can't effectively choke
it.
73,
Jim Brown K9YC
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