[AMRadio] Re: AMRadio Digest, Vol 46, Issue 24


jeremy-ca 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 
>> 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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