Topband: Common mode chokes

[Pete Smith]

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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