Most of us think of the Bobtail as the 3 vertical wire array fed at the
bottom of the center with an LC network. Actually this is a three element
or double Bobtail per designer W6BCX. The half square with two vertical
elements and one 1/2 wave flat top is the actual basic bobtail. One of the
best articles on the bobtail was in a QST about 1973 written by K3BC. This
was re-printed in the ARRL Antenna Anthology (out of print).
There were two variations of the bobtail. One feeds the antenna at the top
(current feed) where you need no tuning network...I.E direct coax feed. You
have to be careful to run the coax off at right angles to the vertical side
at least for 30 to 40' to avoid disrupting the pattern. There was another
version called the Robert's tail which inverted the bobtail (horizontal
sections on the ground).
I remember W0MJ had phased bobtails on 75 SSB 20 years ago. CN2AQ called CQ
and probably 100 called him including some with big antennas on the east
coast. He dropped in his call and got him on the first call at 40DB over
nine.
I have seen numerous gain figures (LB W4RNL probably has a model or too on
his web page). W6BCX thought the bobtail had about 4 db gain.
Bi-directional of course. W6SAI used BCX's 7 to 9 db gain for the 3 el
version at low angles.
I use the half square (regular bobtail) on 75/80 with good success...just
wish I could put up two for 360 degree coverage. At K5MDX I had the 3 el
80 up broadside N/S...did real well except on VE4 and CE. Comparing the
bobtail to a trapped dipole (the 102' version in the 1956 QST) there was
about 3 S points difference in California and 2 S points better in Europe.
Dipole was ne/sw and 75' away.
Dave K4JRB
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