[VHFcontesting] Compact VHF+ beams

[jcplatt1 at mmm.com]

Some great ideas !   Along the same lines of trying to get 6, 2 and 432 on
one small boom antenna, here is the idea that I have been dabbling with.  I
have a partially working prototype.

The antenna is a 5 element 2m yagi where the reflector and the last
director are electrically connected to the boom and the middle three 2m
elements are electrically isolated from the boom.   The boom is then
electrically split in the middle .... you can use a simple wooden dowel.
For 6m, the boom is fed directly in the middle with coax as a shortened 6m
dipole where the two 2m end elements add capacitive loading.   Yea, its
"just" a dipole on 6m, but as a rover if you can get this antenna up 12' or
more it will work.   For 2m, its a conventional 5 element yagi with the
driven element fed directly with coax.   The problem is 432.   The idea is
to use the same 2m yagi on 432 as the third harmonic, but modeling shows
the expected clover leaf pattern, not a lot of gain, and with a null
straight ahead.  This is usable if you understand the pattern, but it can
be made better.   If you tilt the ends of all the 2m elements forward 30
degrees to form a Vee, much like a VHF TV antenna, you can significantly
improve the 432 pattern and actually produce fair gain.   The pattern isnt
as clean as a yagi design for EME, but thats not the design goal.  The gain
and pattern change impact on 2m of tilting the elements forward 30 degrees
is very small, essentially not noticeable.    I have not resolved how to
drive the 432 part of the antenna ..... one thought was that the 2m driven
element could use a 2m gamma match on one side and a 432 gamma match on the
other side (2m and 432 uses the same driven element).    I have not tried
this before and I wonder if anyone else has.   Another option might be to
add a separate driven element for 432, perhaps just ahead on the 2m driven
element, but that needs a lot of exploration too.   Perhaps a sleeve feed
could be used.

If this design could be made to work, it would offer a very simple, very
portable antenna for 6, 2, and 432.   My primary goal was to find a cheap,
easy, portable antenna for guys who have FT100's, etc, who want to give VHF
roving a try without a serious investment.

73, Jon
W0ZQ