Pete Smith wrote:
>
>
> [I forgot the prohibition on top-posting -- resending done *properly* I hope.]
>
> Sometime within the last month or two I recall reading a description of a
> matching
> system for a 2-band vertical (80 and 160, or 40 and 20, second
harmonic relationship)
> that avoided switching altogether by some cleverness with arrangement
of matching
> components. Can't for the life of me remember the specifics, though
- does this ring
> any bells?
>
> 73, Pete N4ZR
Hi Pete...
I have a Titanex V-160 which is about 87 ft tall. While playing around
with EZNEC and a Smith chart, I discovered a matching sytem that worked
on both 80 and 160 without switching. It consists of a (approx) 12 uH
coil from the base of the antenna to ground and a motorized 500 pF cap
from the coax center conductor to the antenna base. The motorized cap
is an old Heathkit SA-2550. The antenna is down now pending relocation
but, if memory serves, it gave a low SWR between 1800-1900 kHz and
3500-3800 kHz.
Another method I've modeled is to have a parallel circuit in the antenna
which cancels the reactance at the feedpoint. For the V-160, a 200 pF
cap and a 19 uH coil located about 46 ft up on the antenna looks like
it would do the trick. This also has the advantage of doubling the
radiation resistance on 160 for less loss. However, the feed R on 160
is about 25 ohms so it still would take some matching. With low loss
coax it would allow you to do the matching with a tuner in the shack
which would allow full coverage of the bands. Somewhere I have a program
that will get you in the ballpark on the component values if you're
interested.
73, Roger
--
Remember the USS Liberty (AGTR-5)
http://ussliberty.org/
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