|[AMRadio] Re: AMRadio Digest, Vol 46, Issue 24|
km1h at jeremy.mv.com
Tue Nov 13 18:16:48 EST 2007
----- Original Message -----
From: "D. Chester" <k4kyv at charter.net>
To: <amradio at mailman.qth.net>
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
>> thru 12:1 powdered iron baluns into coax and filters. I wont even run
>> wire line. I also run 12:1 baluns/ununs on the receivers (2.5V HRO,
>> NC-240D, SX-9, SX-28, HQ-129X, etc) from the coax feedlines and patch
>> 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
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
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.
> 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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