[Elecraft] Tuner efficiency question

[W3FPR - Don Wilhelm]

Folks,

I recall comparisons and analysis of different tuner types done several
years ago by ARRL.  The conclusion was that the inductor Q was the major
determining factor for tuner efficiency of any one type of tuner.  The T
match circuit can match a large range but at some settings can produce high
circulating currents leading to very high losses, the PI network is
generally low loss but at the expense of failing to match very low impedance
loads with reasonable value capacitors, the L network is quite efficient,
but the lowest loss is a link coupled tuned tank circuit type tuner with a
high Q inductor (i.e. Johnson Matchbox type).

IMHO, compact designs have produced more tuner losses than any other
contributing factor - Hi-Q inductors are generally large airwound fixed
coils spaced far away from conducting surfaces.  I look at my Johnsom
Matchbox and see an air-wound coil supported in the center of a large box
(the coil has lots of surrounding empty space), quite in contrast to my MFJ
T match circuit tuner with the roller inductor placed less than an inch from
the side, bottom and top of the enclosure - the front panel appearance of
that tuner was judged more important than minimizing the inductor loss - and
we call it progress!!!

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.  While I have not
seen efficiency tests of the Elecraft tuners, I would venture to guess that
their L network design with switched toroid inductors would show a
relatively low loss compared to many other designs.

73,
Don W3FPR

> -----Original Message-----
>
> I haven't had lots of different tuners to compare myself, but I do have
> a Johnson KW Matchbox tuner.  It does a great job on Balanced lines.  I
> didn't really know about the Palastar but just checked it out on the
> website.  Looked like an interesting tuner.  But to me the downside of
> it was that there is a balun on the output, which of course as Don
> stated is a dominating factor in losses in a tuner (at least maybe that
> is what I took away from his comments as well as other discussions on
> this subject in the past).  Is there a modern tuner out there for
> balanced lines that doesn't use a balun?
>
> Maybe the proper comparison for more apples to apples comparison should
> be made for tuners that are designed for type of feedline output or
> maybe Hi-Z vs Lo-Z, as most today, including the Elecraft, are likely
> ...

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