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

On Wed, 21 Jul 2004 10:51:07 +0300, tj wrote:

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

oh1meq

Hi OM,

Certainly sounds ambitious. As for fixed spacing, you would be
sacrificing an optimal separation, but that would be the least of your
problems as you describe the design.

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).

This describes (I presume) three equal sized elements for either band
(and I would further presume, for bands in between too). What makes
one a director, one a fed element, or one a reflector? If they vary
independently to maintain those relationships; then being fixed top
and bottom by another boom may offer some problem. Then again, maybe
not, it isn't that much different and the two booms would only pull
slightly together.

As for the rectangular shape for the 10M band, that is a very
different feed Z than the more square shaped on at 20M.

You are going to need modeling to be able to find the separations of
the elements that work over these frequencies as well as to find the
feed point Zs. The rest are simply mechanics, which unfortunately may
be the easy part.

73's
Richard Clark, KB7QHC

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