jawod wrote:
Please help a newbie. Can I get a good definition of "common mode"?
I've been reading ARRL pubs but can't seem to get my head around this
concept.


The best explaination of this I have ever seen is contained in W1HIS
..pdf article on yccc.org concerning common mode chokes. Dont let your
head hurt. It is a big download but well worth the read. Chuck is a
retired prof at MIT and did AR commuity a great service by publishing
this. Transmission line vs. common mode is addressed in the early
stages of this read. If you get hooked on this chunk of info like I did
because of receive improvements and TVI redux be sure to read the
footnotes. There is a wealth of info contained in the footnotes.

To give you some idea of the degree of improvement in receive noise
floors....I am using a 33 foot vertical mounted 12 feet up with some
elevated radials. I feed this with a Johnson Matchbox and 450 window
line. Receive noise floor improved by 7 to 10 db after installing 3
common mode chokes in the feedlines. 1 at the feedpoint, one at the
entry and one at the exciter.

I cannot imagine how much money I would have to spend in improved
antennas and hardware to yield that kind of noise redux.

Here is the link:
http://www.yccc.org/Articles/W1HIS/C...S2006Apr06.pdf

BTW. The reason why I started this search on common mode choking was to
reduce rfi in the shack. My installation is meant to offer minimum of
tvi by being careful with my antenna placement which in my case means
having it 12 feet above my transceiver. Not only did the rfi go away
but all my rfi issues subsided on my entertainment devices as well. No
complaints from neighbors either. On smallish city lots with open door
entertainment systems makes it hard to be a good neighbor. This helped
a bunch.

Best and good reading, Chas W7MAP/5