I gave contesters and Dxers a challenge to build a G4ZU Birdcage for either
80 or 160 a couple of years ago.
I don't know of anyone who has one, but I do know that many are looking for
a way to improve their signal over a four square
or even a set of K8UR vertical dipoles. The G4ZU birdcage (see CQ Magazine
April 1960) is a 2 el quad folded back on itself
G4ZU found that using just a portion of the birdcage (the bottom X) gave
almost the same results. He labeled this the X beam.
Moxon G6XN noted the defect with the X beam was spurious radiation off the
sides. W9PNE used wireback wires to cut these side emissions (See the ARRL
Antenna Compendium Vol 1). There was an excellent article in a 1991 73
magazine, too.
I have used the X beam with wirebacks on 12 meters for 6 years and have
worked 306 DXCC countries. W9PNE says it performs like a 3 el beam on the
design band, but its only a 2 el beam with driven element and director (very
close spacing) so I feel that it has or approaches 5DBd of a 2 el beam. It
does compete with the A3WS and similar beams. This could be adapted to 80
meters and since it has NO BOOM (it appears as a 64+ foot X) this appears to
have reasonable probability of giving one a 5Dbd directional beam on 80. It
has
fairly wide 2 to 1 swr footprint but would probably require relays to switch
between CW and SSB (3505 and 3795).
This beats or exceeds most of the short beams on 80 and would be a lot less
trouble to maintain. On 12 I have 10 to 15 DB front to back
and 25DB front to side with sharp nulls at several points. It is 5.5 feet
below my KT34XA and does not seem to interact. I would guess
it would need to be 10 feet or more away from a 40 meter beam.
Any takers? If I can find the right materials I would put one on my tower
but its at a max now.
73 Dave K4JRB
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