[Amps] RF in the Audio

Carl km1h at jeremy.mv.com
Sun Sep 25 17:23:33 PDT 2011

 I have all QST's from 1926, CQ from #1 to 1972, all HRM, dozens of both 
handbooks and like to read.

Antenna tuners were always popular subjects and some were really elaborate. 
One fully balanced unit had many patch cord sockets and could be configured 
any possible way you could think of and covered 160-10M.

The last tuner I had was an almost new Drake MN-2000 around 1965. It was a 
PITA to use in any sort of contest or DX chasing enviroment and thats when I 
started modifying the amp to be the tuner. That NCL-2000 is still in use at 
the vintage SSB station.


----- Original Message ----- 
From: "Paul Christensen" <w9ac at arrl.net>
To: <amps at contesting.com>
Sent: Sunday, September 25, 2011 5:32 PM
Subject: Re: [Amps] RF in the Audio

> Cebik's material covers a significant amount of design and historical data
> for link-coupled tuners.  W9CF, W7EL, W8JI and others have shown that
> placement of a CM choke at the input of a tuner only offers a benefit when
> the tuner is symmetrical.  (e.g., AG6K type, and not T, L, nor Pi types).
> Specifically, W9CF writes:
> "As noted by Roy Lewallen, W7EL,[2] putting a choke balun on the input of 
> an
> unbalanced tuner to drive a balanced line is useless. It introduces a
> ``hot'' tuner case which must be isolated with no benefit over putting the
> balun on the output."
> See http://fermi.la.asu.edu/w9cf/articles/balun/
> Since the traditional link-coupled tuner performs the BAL-UN function 
> across
> an air core RF transformer, no CM choke is required.  The unbalanced input
> side of the tuner is formed by a tapped link, and in some cases, one side 
> of
> the link is in series with a variable shunt C to ground.
> Cebik's material also discusses similarities and differences between
> link-coupled tuners that require the re-tapping of the output coil as well
> as the output "voltage divider" tuner (e.g., Johnson Matchbox)
> Paul, W9AC
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