[Elecraft] KAT500 update

[Don Wilhelm]

This is of interest to me, because in my first experiences with antenna 
forums (or was it newsgroups at the time),  I recall a lot of exchanges 
with Tom W8JI on exactly the "balun at the tuner input and isolated 
unbalanced tuner".  I concur with Tom - it does not work -- both from a 
theoretical basis, and also from Tom's measurements.

This was "way back when" - as I recall my situation when all this was 
going on, I was running Windows 95 and the year was between 1997 and 1998.

In the timeframe of this discussion, Zack Lau (ARRL engineer)  who had 
first published the "balun at the tuner input" concept as a QRP tuner, 
had retracted that design because it did not maintain balance, but Dean 
Straw (ARRL engineer, editor, etc.) published his design of a high power 
tuner using the same concepts, and that design can still be seen in the 
ARRL publications.

Apologies for the comments into the politics of the ARRL decisions on 
what is to be published, but that is both a bit of the history as I know 
it as well as my view of the technical side of this issue.

If anyone can tell me how you can run a signal through a balun - and 
have equal and opposite currents at its output, and then run it through 
an unbalanced network with unequal elements in the two series legs and 
still maintain equal and opposite currents and phase, and I will then 
concede that an isolated unbalanced tuner with a balun at the input will 
work, but until that is presented to me along with detailed engineering 
level test data (not just "it works"), I will continue to believe that 
using a balun on the input of an isolated unbalanced tuner is a "pipe 
dream" that does not mesh with reality.

73,
Don W3FPR

aOn 12/8/2011 6:28 PM, Eric Swartz - WA6HHQ, Elecraft wrote:
> Hi Ignacy,
>
> This is a common misconception. (One which I held until recently. :-) It
> turns out there is no advantage to placing the balun at the input of the
> L-Network tuner. Since one end of the balun is grounded by the input to
> the tuner, it is still presented with the same stresses under high SWR
> situations. Baluns at the input and output both drive balanced loads
> equally well.
>
> We've now put together a web page describing the impact of placing the
> balun at the input or at the output of a L-Network tuner. See:
>
> http://www.elecraft.com/KAT500/input_versus_output_balun.htm
>
> At the bottom of that page are several links providing detailed
> technical analysis of these configurations. The first two, by W8JI and
> W7EL are very clear discussions of this issue.
>
> 73, Eric   WA6HHQ
>
> www.elecraft.com
>
>
> On 12/8/2011 3:17 PM, Ignacy wrote:
>> It seems to me that the story is more complex than it sounds.
>>
>> The input balun always works at low SWR and at 50 Ohm. It is very easy to
>> have such  balun. A small balun would easily handle a KW without heating.
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