On Fri, 21 Nov 2008 08:26:52 -0700, Tod -ID wrote:
>Please help me understand why an 'RF resistor' should perform differently at
>one end of a wire compared to another. ?
Because the wire in question is long enough to behave as an antenna at some
frequencies of interest. The portion of the coax betwen the choke and the
intentional RX antenna will act as a separate antenna, and any voltage received
on it will couple into the intentional RX antenna and distort its pattern. The
pattern distortion defeats the directivity of the intentional RX antenna. If,
for example, the coax is close to a half wavelength, it's a near ideal antenna,
so it couples even more voltage onto the intentional RX antenna.
The function of the choke (you're right in viewing it as an RF resistor)
decouples the transmission line from the antenna.
Gary, KA1J, asks:
>Excuse my ignorance but on a receiving only antenna like the K9AY,
>what is the difference I will experience between having an excellent
>choke and no choke on the K9AY feed?
For the reasons above, it makes the performance of the K9AY closer to ideal.
On Fri, 21 Nov 2008 07:41:35 -0600, Rick Hiller wrote:
>GM. Can you refer me to your postings (dates) or web site with the info on
>the chokes that you have recommended?
I posted it yesterday. Perhaps you deleted the post without reading it. :)
http://audiosystemsgroup.com/RFI-Ham.pdf
>I thought the Palomar kits were based on the W2DU chokes, they might be, but
>then again we are talking Top Band here....a bit of a different fish.
W2DU's work is excellent, but it was done 30 years ago. My work, as described
in the tutorial above, takes his work the excellent work of W1JR done around
the same time, and much more recent work by W1HIS and builds upon it. The
result is that the chokes I've described and that you can easily build are far
superior to theirs.
Palomar is primarily a seller of parts, not a great engineering company. W2DU
and W1JR are great engineers. I'm also an EE, and I've done extensive work on
ferrite chokes. Before I began my research, I bought what Palomar sells as
balun kits. They don't even begin to make a GOOD W2DU choke, and my chokes are
much better than W2DU chokes. Note that I'm not selling anything, I have no
money interest in this. I've simply done a lot of research and published it.
For free.
All of this is described in the tutorial posted above.
73,
Jim Brown K9YC
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