View Single Post
  #6   Report Post  
Old July 26th 05, 04:55 AM
 
Posts: n/a
Default

However, it appears I would be
better off with feedpoint inductors instead of putting them halfway out
the legs of the dipole.

Myself, I would prefer them out at 1/2 or even 2/3 from the center.
Better current distribution. What will the antenna be made from?
Wire, or metal tubing? Regular solenoid coils can be made from
any light plastic tube, using light wire. I use insulated wire to act
as a spacer. I then cover them with shrink wrap, or tape.
If the antenna is hard to match to coax, you can use a third coil
at the feedpoint, and tap it for the best match.
If the antenna was tubing, I would use wooden dowel that would
fit in between a section of metal tubing, and wind the coils on those.
I'd weatherproof those some way also.
When I make small loaded dipoles, I think exactly the same way as
I would designing a mobile whip. I'd make the most efficient design
of a 24 ft whip, IE: coil placement, etc, and just double it for a
dipole.
Whats best for a short whip, will also be best for a short dipole
of the same size per leg. The very best location is probably at
the 2/3 to 3/4 mark, but it's not that critical. Even 1/2 out is good.
Reg's vertload can model all that, and tell you the best place, coil
info, etc, etc... In comparing to the real world, it's close nuff for
gov
work. If the apex was high, even a center load could be ok, but if
you only have 5 watts, I would go for every last scrap of efficiency
in the design. Actually, I'd also carry a spare 120 ft of wire to use
as
a full size dipole in the off chance the location could support it. :/
Many would, if they have trees to hang wires from, etc.. Even if the
full dipole is perverted, and making turns, a "Z",etc, it will usually
outdo
the loaded antenna for 75m.
MK