[Elecraft] Tuner efficiency question

[Jim W7RY]

There is a fellow here in the NW that builds link coupled tuners. Pat 
Buller, W7RQT.

They are quite well made and look great. His email is shown on www.qrz.com


73
Jim W7RY


ConAt 09:30 AM 5/13/2005, al_lorona at agilent.com wrote:

> > ...
> > Contrary to popular belief, balun loss is not the largest
> > contributing factor, and if properly designed, makes
> > little difference whether it is placed on the input or the
> > output.  Charles Green W1CG has done a lot of work
> > on balun loss and reports that the loss is actually
> > quite low (even when their design impedance is
> > severly mismatched).
> >
> > My bottom line conclusion here is that we pay a price
> > in efficiency for the convenience of compactness and
> > a large matching range.
>
>Yes, we most certainly do. Too many of us care only about the automatic 
>aspect of these compact tuners, and we give up really efficient tuner 
>operation. Tuners have to be really large to be really good. The 
>components have to be large and the enclosures have to be large. But 
>because many people don't like large boxes on their operating tables, and 
>because they would rather not twiddle knobs, they go to these small, 
>sometimes lossy autotuners. As long as they understand what they are 
>giving up by doing this, it's cool.
>
>However, balun loss isn't the only important factor and may not even be 
>the most important factor. The balun's primary purpose is to convert to a 
>balanced two-wire system, and in order to preserve the antenna pattern and 
>keep the feedline from radiating, it has to provide equal currents in each 
>leg of the feedline. In order to be effective at this, the balun's 
>impedance has to be large compared to the antenna's input impedance. When 
>baluns in tuners have to look into very high impedances, they stop acting 
>as baluns. You may be happy that a particular balun doesn't have a lot of 
>loss, but you would be very unhappy to learn that that same balun isn't 
>doing it's job as a balun anymore. Under these conditions, who knows what 
>the antenna pattern is.
>
>Using a balanced tuner gets you part of the way to a highly efficient 
>antenna system; the other half of the journey is to use a balun-less 
>design that attains true balance no matter what the antenna/feedline 
>conditions are. I have found this possible only by homebrewing such a tuner.
>
>I don't know if you've ever seen the Annecke tuner on L. B. Cebik's web 
>site:  http://www.cebik.com/link/link.html . It was the best hope we've 
>had to seeing a link-coupled tuner like the old Johnson Matchbox, and many 
>folks were expecting it to go back into production, but the person who 
>bought the rights to the design has decided not to pursue the manufacture 
>of the tuner at this time. Too bad. We'll just have to keep building them 
>ourselves.
>
>Al  W6LX
>
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