Ben Jackson wrote in
:

I've used a couple programs (vertload.exe and I think LODI) to design
a shortened, single band dipole antenna for 30m. Specifically I'm
interested in 10.149MHz.

Ah, the good old 10.149 packet net? I used to run a node on there
(VE1EI) a fey years ago.

The result is:

--1m wire--[~34t 1.5" form 2" long, ~24uH]----2m wire----[center]--...

The center would be a 1:1 current balun, twisting the wires together
and then taking 10-12 turns on FT50-61 (or if that won't fit, fewer
turns on FT50-43).

The predicted resistive input impedance is 22 ohms. Vertload is just
simulating half the antenna (with 0 ohm ground loss) so its match info
is not useful. The other program called for a ".71uH matching coil"
for 50 feed, which I assume is to cancel a calculated -j45 reactive
component??

I would like to pre-calculate an approximate match to Z=50ohms which
I can put directly at the feed point and shrink-wrap with the balun.
Is there a way to do that, or is it too touchy to do without measuring
the actual antenna?


How high is this antenna and above what kind of ground?

For 15m high, I get values of 21.21 microhenries and 9.85 picofarads
across the feedpoint (you could make that out of a short coax stub). SWR
would be 1.82 to 1 on 50 ohms, though. That could be improved upon by
altering the length of the outer wires a bit and tuning the capacitor to
match.

--
Dave Oldridge+
ICQ 1800667