----- Original Message -----
From: "D. Chester" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Tuesday, November 13, 2007 3:20 PM
Subject: [AMRadio] Re: AMRadio Digest, Vol 46, Issue 24
I wont even run open wire line.
All my old rigs (even the PP 211's) will be running from balanced PP
output
thru 12:1 powdered iron baluns into coax and filters. I wont even run
open
wire line. I also run 12:1 baluns/ununs on the receivers (2.5V HRO,
NC-101X,
NC-240D, SX-9, SX-28, HQ-129X, etc) from the coax feedlines and patch
panel;
it makes a big improvement.
In all my years as a ham I have never used a balun or coax feed to a
dipole. Always used open wire line with a link-coupled tuner. That gives
far better harmonic suppression than feeding through a balun directly to
coax, which offers no selectivity whatever between transmitter and
antenna. Besides, the efficiency of baluns sucks, unless they are looking
into a purely resistive, nonreactive load at the rated impedance. Many
of the modern commercial tuners use an unbalanced T network into a balun
for open wire balanced feeders. Bad design, those things are notorious
for running hot, since a balun was never intended to work into random,
highly reactive loads.
The thing I like best about open wire line with a tuner is that one dipole
will work from one end of the band to the other with equally good
performance, and you can work multiple bands with one dipole. I don't
like the idea of nest of dipoles all over the place, to interact with each
other and tangle up in heavy windstorms, not to say how cluttered it
looks.
I havent used open wire line since I was in high school in the 50's.
If that is all you are able to get in the air then I agree it is a fair
compromise that has been used going on 80 years. However I will be using my
regular station antennas which include 4 Squares on 160 and 80, backed up by
switchable coax fed inverted Vee dipoles at 180' and 50', and a 2 over 2
yagi on 40M. Higher bands have stacked yagis also and spread over 4 towers.
Every antenna is monoband and individual band filters are used in the shack
as well as a few coax stubs. In the past this was a very active contest
station that could run 1500W on several bands at once with no inter station
interference; harmonics is not a concern. There isnt an antenna tuner on
the property and the station was designed for maximum operator efficiency
when changing bands or moving within a band. Certainly overkill for AM
ragchews but its already there and working and I spend a fair amount of time
chasing DX on CW and SSB..
Baluns work very well with efficiencies over 98% into even moderately
reactive loads when constructed properly. I have a reactive dummy load that
National used to test a military KW amp back in the 60's ( I built it then)
and can go anywhere over a 2:1 VSWR range at a full KW and barely feel a
difference in temperature from the pure 50 Ohm point.
The problem with More F Junk and many other commercial tuners is they try
and convince you that one size fits all from 1.8 to 30 MHz. Then they catch
on fire.
Catching up and relearning all I forgot about AM will be interesting and
fun; Ive already learned a lot in the short time Ive been on the forum.
Many thanks to all.
Carl
KM1H
In the past I have run single wire antennas directly to the transmitter,
without using any kind of measuring equipment at all other than trial and
error, and watching how the transmitter loads up. You can estimate pretty
well what kind of impedance the end of the wire should have, if you know
its length and know the frequency you are operating it on. Of course a
thermocouple rf ammeter is very useful. Another good rf indicator is a
neon lamp.
But attaching the single wire to the tank circuit without any kind of
tuner is asking for a pink slip for harmonics.
Don k4kyv
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