[Elecraft] High power tuner

[Don Wilhelm]

Just because it was published by the ARRL does not make it a good 
design, although it might help to sell a few.

Zack Lau published a QRP version of that tuner some years back and later 
retracted it, and it has not been mentioned much since, but Dean Straw 
published his high power version of about the same design and that seems 
to be the "best thing since sliced bread" despite counterclaims by noted 
authorities on balun and RF designs - W8JI, W7El and others.  Bottom 
line, it just does not work well, although there will be many who will 
say that "Alpha makes good stuff", that still makes it a stretch of the 
laws of physics - using an unbalanced network "floating" (although not 
really isolated from a common reference (ground)) will still not make 
everything balanced.

I know there are those who will claim that an off center fed dipole has 
a balanced feedpoint, but I am not convinced.  I put the "balun at the 
input" tuners in the same category.  Take a balanced signal (output of a 
balun) and feed it through an unbalanced network, and claim that the 
output of that unbalanced network is balanced just does not make much 
sense to me.  Maybe with ideal components it *might* be possible, but if 
one would plot the reactance and phase delay around that unbalanced 
network using good scientific methods, it would become obvious that the 
output would not be of equal and opposite currents with 180 degrees 
phase difference.  If the schematic does not look balanced, it is not 
really balanced.  Follow the leading current and lagging current around 
the circuit to convince yourself.

73,
Don W3FPR

On 11/26/2011 10:10 PM, David Gilbert wrote:
> If I remember correctly, the announcement for the Alpha tuner even
> stated that they "drew heavily" (or words to that effect) from the ARRL
> Antenna Book for the design.
>
> 73,
> Dave   AB7E
>
>
>
> On 11/26/2011 6:37 PM, Paul Christensen wrote:
>>> I was surprised to see this from Alpha, whom I would have expected to know
>>> better.
>> The identical design (less automated functions) can seen in recent issues of
>> the ARRL Antenna Book  For example, see 20th Ed., pp. 25/15 - 25/19 and
>> titled "High-Power ARRL Antenna Tuner for Balanced or Unbalanced Lines."
>> Even output C is the same at 800 pF max.
>>
>> Paul, W9AC
>>
>> __
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