"Cecil Moore" wrote in message
...
Frank wrote:
The nominal impedance of a 40 m dipole on 20 m, at 30 ft above
an average ground, is 4700 + j0. There may be some inductive
or capacitive reactance present --depending on the exact length
of the antenna -- but it will not effect the transmission line losses
significantly.

100 ft of RG 58 exhibits a total line loss of about 13 dB when
terminated with the above impedance. i.e. 100 W in gives 5 W
radiated.

This seems a bit academic. I don't know anyone goofy enough to
run 100 feet of RG-58 with 100:1 SWR; do you?

While 1/4WL (or 3/4WL or 5/4WL) of 450 ohm ladder-line yields an
impedance at the transmitter of 43 ohms for a 50 ohm SWR of 1.16:1
without a tuner and very low line losses. What could be sweeter?

What could be sweeter? I'd say a 20m dipole, coax fed. (Mine shows
1.0 SWR at band center, and under 1.5 full-band. Not fussy about feedline
length. Feedline also runs through a metal conduit, with no problems.
No tuner of ANY kind needed, distributed or conventional. Minimal
loss. QRO FB.)

But if one MUST operate a doublet far from 1/2-wave resonance, then
a balanced feedline plus tuner is the way to go. And implementing the
tuner in distributed form by tuning feedline length has some advantages
over a conventional, lumped-constant tuner. To my mind, the MAIN
advantage of the tunable feedline is that it can handle high power at
low cost. I'm a bit surprised you don't talk that advantage up more.

73, Ed, W6LOL

--
73, Cecil http://www.qsl.net/w5dxp

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption
=----