For several years I have toyed with a simple 6, 2, & 432 antenna that could
be deployed for roving or portable use. Size, weight, cost, simplicity,
play against gain & performance, so there has to be trade offs. Here is a
thumb nail sketch of my design so far -
1. Single aluminum boom, length is five feet.
2. The boom is electrically isolated in the middle where direct feed coax
is attached for 6m operation .... the boom acts as a 6m dipole (keep
reading).
3. There are five 2m yagi elements mounted to the boom - the last director
and the reflector are electrically common to the boom and act as
capacitance loading to get the boom to resonate on 6m. The three 2m yagi
elements that are inbetween the last director and the reflector are
electrically isolated from the boom and are not players on 6m.
4. On 2m, the antenna is a standard 5 element yagi, feed type is TBD.
5. When you feed the 2m yagi on 432, you get what you expect from a 1.5
wavelength antenna - a clover leaf like pattern with a null straight ahead.
By sweeping all ofthe 2m yagi elements forward 45 degrees to form a "Vee"
shape, much like a standard VHF TV antenna, it sharpens the 432 pattern and
has very little effect on the 2m performance. The pattern on 432 is not
ideal for say EME, but it has the desired pattern, F/B, and gain.
So on 6m, the antenna is a simple dipole with its own separate feed where
the boom is the dipole with end loading provide by the two 2m elements on
the ends. On 2m, although the elements are swept forward by 45 degrees
into a Vee shape, its pretty much a standard 5 element 2m yagi. On 432,
you use the same antenna as the 2m yagi where the forward sweep provides a
pattern and gain - the desire is to have one coax feed for 144 and 432 so
that it matches up with a 706. As the antenna is light and small, its
easier to get higher in the air. A 6m dipole at 20' is better than a 3
element yagi at 8 feet (speaking about roving of course).
What I have not solved yet is the 2m/432 single coax feed. There is a lot
of interaction there between the two bands and the few things that I have
tried have not worked. Perhaps two gamma matches with a common feed ?
Maybe separate band dipole feeds ? Any suggestions?
I showed this antenna design concept on a poster board at Aurora 2008 which
is our clubs annual gathering, so its had public exposure. I still have
the EZNEC file and would be happy to share what I have so far with anyone
who may be interested, just drop me an email.
73, Jon
W0ZQ
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