Alas, on the wretched hour of Thu, 04 Jan 2007 09:56:29 -0800 K7ITM
thusly proclaimed:

Ceriel Nosforit wrote:

measure twice, snip once

Well, this is basically a "go for it." I'm not quite clear on how you
are going to stack up the plates when you're done...what holds them in
position and so forth. One advantage of the "normal" semicircular
plates is that there's not such a long piece of metal hanging off the
rotor shaft as you will have, assuming the shaft runs through the
"pointy" end of the rotor pieces. Beware of what vibration does to you,
in other words. As thick as your plates are, I suppose that won't be a
problem.

The widest-range variable I have is built with circular plates, with a
tab off the edge of each through which the rotating shaft goes. There
are actually two rotors, which are coupled through equal-size gears on
each shaft, so one rotates clockwise as the other rotates
counterclockwise. The plates go from full mesh to full separation, and
give over 100:1 capacitance ratio from max to min. The shafts must be
insulated from each other, of course. There's some advantage to a
capacitor with a wide tuning range in an ATU, in getting the ATU to be
able to cover a wide range of matching impedances over a wide range of
frequencies. Anyway, I suppose you could do something similar with your
rectangular plates.

Cheers,
Tom

Hello Tom. Thank you for your reply.

I'll separate the plates with spacer disks and bolts on a 6 mm threaded
steel rod, indeed through the pointy ends. 6 mm is IMO too thin on its
own, but the disks and bolts should add a lot of stability. The entire
thing will be propped up on plexiglass plates at the ends, and I'll have
one additional 6 mm threaded steel rod where I marked 60 degrees on my
schematic. If it still not stable I'll add something to the top and bottom
to keep the rods stretched straight. If that still isn't enough, I'll have
to build some sort of support for the mid-section.

The blades will separate from each other more than completely, if I want
to. I don't know the electrical implications of what would happen if I did
so. I guess at some point the curcuit would simply be broken... Maybe
permanently? Either way, infinite ratio from max to min.

I plan on either adding a counter-weight, a rubber band, or some mechanics
to keep the rotor from simply falling down. A counter-weight should give a
nice 'feel' to the dials, which is very important for any sense of
"quality".

If the parts of the ATU turn out reasonably pretty I'll make an enclosure
largely out of plexiglass for them. A cardboard box is however a lot more
likely. I expect the end result to look horrible and work marginally
better. XD

--
Nos