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, 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> 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
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