take a gander at this quad.....only one driven element...
http://www.titanex.de/frames/quads.html

"tj" wrote in message
...
Hello,

Steppir has the tunable yagi antennas:

http://www.steppir.com/products/prod-3el.htm

In those, the yagi element lengths are changed according to each band. I
am thinking of doing a homebrew antenna based on the same principle. My
antenna would be a three element quad. It would have two booms, both
having three 4m long horizontal glasfibre pipes. Thus, the boom with the
pipes would look like a 3-el yagi. The upper boom would be attached to
the tower and the lower boom would be hanging from the antenna wires of
the three elements. The lower boom would go up and down depending on the
band and the total loop length. The three motors would be located on the
upper boom. The wire would propably be a steel wire. With 4m pipes the
distance of the upper and lower boom would vary from 1m (4m+1m+4m+1m=10m
band) to 6m (4m+6m+4m+6m=20m band). On the end of each pipe there would
be a small wheel to assist the sliding of the wire.

The whole thing would be microprocessor controlled (8051, Atmel AVR
etc). At the beginning it would have to be tuned to each band in order
to extract the correct loop lengths. The lengths would be stored to the
flash memory of the microprocessor.

What do you think? The element spacing would be fixed, is that ok?

oh1meq