After my recent move this summer from Spokane,WA (one of the great radio
black holes) to a new venue just south of Green Bay, WI ( a lesser back
hole..trust me!) I finally got around to putting up the first beverage.
Being a scotchman by ancestory the two wire beverages have always appealed
to me because of the economy of being able to use ONE set of poles for TWO
antennas, and ONE Coax feedline (with a relay to switch in TWO directions.
Also having had very good success with my 580 ft 2 wire center fed Beverage
systems in Spokane I set out to reconsruct them again.
Having the room at this QTH I fell victim to the bigger is better trap so I
put up a 720 foot two wire Bev. as the first antenna. As predicted by Misek
and W3LPL and others the first thing I noticed is that the front to back
performance of this non optimal "cone of silence" length was noticeably
poorer when compared to my old 580 ft antenna. Once again theory and
reality converge!
Never having been one to let well enough alone I started modeling the
antenna using Brian Beasly NEC WIRES 2.0. I've done this enough times to
know that reality and NEC WIRES dont always agree, but it does often
provide insight into which way a design ought to be pushed. I started out
by modeling the antenna as a single 720 ft wire Beverage terminated on one
end and fed at the other. As predicted there is an optimum termination
resistance for any Beverage which provides optimum front to back as those
of you with variable resistor schemes on your beverage terminations will
attest. What surpirsed me is the model suggested that a termination
resistance for this particular antenna of 175 ohms would increse the front
to back to nearly 30db! The 580 footer had a predicted optimum at closer to
500 ohms as expected.
Everthing is now buried in ice and snow so further experimentation will
likely wait till next March. The above observations do raise the following
questions in my mind however:
1) Does anyone have any practical experience with trying to terminate a two
wire beverage with other than the Ground-Open approach (i.e. with a reistor).?
2) Has anyone out there used a center feed system on a single wire
Beverage? If so tell us more. I have seen one approach that fed the
antenna at odd quarter wave points from the unterminted end but this
antenna does not seem to work well on any but the design frequency.
3) Has anyone out there built a two wire system but fed each wire
seperately from the
far unterminted ends. Will there be interaction and coupling from the other
parrallel Beverage antenna. Performance degradation???
Feed #1 -----------------------------Ant #1
=>---------------------Tremination R
Termination R -----------------------------<=Ant
#2----------------------Feed #2
Regards
Dave K9NX
n7ex@athenet.net
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