Inteesting. Are your assumptions changed by the presence of the
amplifier at the base of the whip, which is designed to match to
75-ohm cable? I will give the beadless version a try.
73, Pete N4ZR
At 09:24 PM 7/4/2009, DAVID CUTHBERT wrote:
>Very good. Another experiment would be to ground the coax shield 20'
>from the antenna as you did but with no ferrite beads. I suspect you
>will see similar results.
>
>Yes you have a 108' dipole comprised of an 8' whip and 100' of coax
>shield. The 8' whip presents an impedance of 3000 ohms and it would
>take many, many beads build a balun having an impedance much greater
>than this.
>
> Dave WX7G
>
>On Sat, Jul 4, 2009 at 8:16 AM, Pete Smith
><<mailto:n4zr@contesting.com>n4zr@contesting.com> wrote:
>I thought readers here might be interested in some crude experiments
>I have been doing here with a Clifton Labs active antenna and various
>common mode choking schemes. It's conventional wisdom that small
>antennas like this need common mode chokes to keep feedline pickup
>from diminishing directivity or increasing the overall noise
>floor. What I didn't realize was how much difference it could
>make. My noise floor dropped about 20 dB by using the
>center-grounded type of bead choke instead of the same number of
>beads, in the same place on the coax, without the center tap.
>
>You can take a look at my results at
><http://wiki.contesting.com/index.php/Common_mode_chokes>http://wiki.contesting.com/index.php/Common_mode_chokes,
>
>which is an
>Open Notebook on the Contesting Compendium. The Open Notebooks idea
>is based on a concept called "Open Wetware"
><<http://openwetware.org/wiki/Main_Page>http://openwetware.org/wiki/Main_Page>
>for sharing scientific
>research in progress. At K3NA's urging, we've incorporated something
>similar in the Compendium as a place for contesters to share their
>projects and experiments while they are in progress, in the hope that
>others will see, comment, and improve.
>
>Take a look, and tell me what you think!
>
>73, Pete N4ZR
>New Articles Daily - the Contesting Compendium at
><http://wiki.contesting.com/>http://wiki.contesting.com
>The World Contest Station Database, updated daily at
><http://www.conteststations.com/>www.conteststations.com
>The Reverse Beacon Network at
><http://reversebeacon.net/>http://reversebeacon.net
>
>
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