[TowerTalk] Re: Building Reversible Beverage Boxes

[Tony and Celia Becker]

Hi Tom and All!

Last winter Ken Keeler put up a nifty reversible two wire beverages
patterned on Tom, W8JI's, article in Communications Quarterly of Spring
1997 at his multi-multi contest superstation, N6RO.   These plans were made
at a local gathering last January organized by Ken and attended, (besides
us plebs) by such luminaries as Dave Leeson, W6NL (ex W6QHS), and Dean
Straw, N6BV, (author of the ARRL Antenna Book).  The entire group was
enthusiastic about the antenna's potential, so off we went to build them.  

Ken has now a NE/SW beverage made of 430 window ladder line at 9'- 10' with
boxes built by me at each end.  I used a "Red Dot" outdoor receptacle box
covered with a piece of 1/4" black Plexiglas, with all the internal
components mounted on the cover.  I made the transformers exact copies of
the ones in the article; I even used the same Amidon beads Tom described.

Ken also has a NW beverage built of house wire and it has a commercial
(ICE?) transformer at the feedline end with a high pass filter to keep the
BC intermod products down to a minimum.

In comparisons from one to the other, Ken reports that the birdies are  10
- 20 dB higher on the reversible beverage.  I suspect that this is due to
non-linearities in the transformers, so any filters would have to come
between the antenna and the transformer to be effective.  What is your
opinion?

1.  Would a larger core (say a 1" toroid) be more linear and produce lower
birdie levels?

2.  Have you any knowledge of how to add BC filters on a reversible beverage?

I am also a bit concerned that the metal box at the feedline end provides a
potentially unbalanced capacitive coupling path between the reflection
transformer and the impedance matching transformer in the main box.  I
really don't know how important it is to shield anything.  I don't think
the extra shielding provided by the metal box can do much about the
multi-multi interference.  Consider that the entire beverage antenna length
is in the near field of a bunch of other transmitting antennas and is
entirely unshielded, (or it wouldn't receive any signals)!

Any comment?

73


AE0M, Tony Becker - becker@sprintmail.com - Silicon Valley, USA

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