> One thing that I've never seen mentioned anywhere is a
multiple-band dipole fed with ladder line. The reason I'm
curious about it is that I used to have an 80-Meter Inverted
Vee fed with ladder line, and the performance was great on
80M. For 160M contests, etc. I would add about 65 feet to
each leg so that it became a full-sized Inverted Vee for
160. However, in doing that, even though the tuner matched
it just fine on 80M, my great 80-Meter performance went away
until I removed the 160M extensions. I always wondered if I
could have had both, if I had built up a combination 160 and
80M Inverted vee with both sets of elements off of the same
ladder line feeder, like may people do with coax-fed
multiple dipoles. Anyone ever try something like this?
>
> LJ
Sorry about the blank reply.
The reason 80m performance went to heck is very likely the
high SWR. On 80 meters the end-impedance of each dipole half
might be 4000 ohms or so. That would amount to an 8000 ohm
load terminating the feedline. If you had 400 ohm line, SWR
would be 20:1 meaning impedance at the tuner might be
between 20 and 8000 ohms. The tuner might not like some
impedances in that range.
If you had a 80/160 dipole, SWR would be limited to about
10:1 (or less) on 160 and 80 on a 400 ohm line. That would
mean an impedance range of 40-4000 ohms is possible
depending on feedline length.
73 Tom
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|