[TowerTalk] AV-640 (was GapChallenger ComparisonTesting Studies)

[Joe Subich, W4TV]

On 4/26/2010 6:44 PM, Dan Schaaf wrote:

 > And the antenna book also mentions that the single wire feed Windom
 > produces RFI in the shack and it works against a ground. And the
 > single wire feed line also is a radiating element.

The ARRL Antenna book is wrong in that regard.  The whole design of
the original antenna that Loren Windom reported on was to solve
the RF in the shack issue by matching the impedance of the single
wire feed to the impedance at the connection point.  This made the
single wire a "flat," non-radiating line.  If the single wire, off
center fed antenna had any significant RF in the shack or feed line
radiation, it wasn't a Windom in your definition of the term.

 > But definitely not a Windom as it was originally designed with a
 > single wire feed and no break in the horizontal wire.

The presence or absence of a break at the feedpoint is not material.
If the single wire fed "Windom" is operating as a true "Windom"
with a flat (non-radiating) feedline, the operation antenna pattern
is identical to a parallel wire fed or coaxial/balun fed "pseudo-
Windom" as long as the feedline version is also operating with no
unbalance current.  Even in the "real world" where none of the
"Windom like" antennas operate with truly non-radiating feedlines,
the levels of feedline radiation and RF in the shack are similar.

 > And my AV-640 does NOT provide RFI in the shack.

You AV-640 does not provide RF in the shack because of the large
current balun (also known as a common mode choke) located in the
"matching unit."  The ability to use a common mode choke is a
major advantage of converting a Windom type antenna away from the
single wire feed.

73,

    ... Joe, W4TV