[Elecraft] (no subject)

[Fred Townsend]

David I have no opinion on Juma, the company or its products. I have no dog
in this hunt. I was speaking to what I consider to be the facts. Perhaps my
poor attempt at humor mislead you. I was speaking to the differences of
internal versus external amps and the use of feedback.

Back in amplifier school I was taught the way to make a 10 db amplifier was
to design a 100 db amp and use 90 db of feedback. That's because feedback is
a the miracle cure for many of the problems that plague amplifiers. And
before many of my colleagues chime in I know 100 db of high power RF gain is
impractical (I can do 60db with a klystron). 

Now my original point. The KX3 CAN NOT make any external amp better because
you can not enclose the KX3 in the feedback loop. Feedback can be used with
the exciter if the exciter and amp are in the same box (i.e. K3/100). That
doesn't make it impossible to design a good external amp, it just makes it
more difficult.

 

It has been suggested in other threads that the Ten-Tec amp is priced higher
than a KPA3 because of hardware packaging issues. This is true but it is
also true that feedback issues make it is harder to design external amps
than internal. Ten-Tec* or Juma* it's Apples to oranges when comparing
internal to external amps and their exciters.

 

73 

Fred, AE6QL

* The claims of these manufactures are the responsibility of their
respective owners.

 

From: David Robertson [mailto:kd1na363 at gmail.com] 
Sent: Wednesday, August 15, 2012 4:57 AM
To: ftownsend at sbcglobal.net
Cc: elecraft at mailman.qth.net
Subject: 

 

Fred,

Thanks for your comment. I have to assume you have a less then staller
opinion of the Juma PA-100-D. Well with -28 db third order IMD this
specification matches the K3-100's IMD spec. and this is with 100 watts out.
All the reports I have gotton reported no problems with my signal, including
those using panadaptors. You mentioned the price, well find a linear that
had the same ability as the Juma PA100=D for less. It looks like it matches
the new TenTech linear for around $700.

 

I am only a consumer, I have no business interest in Juma but for a little
company started by 2 hams in Finland with a lot of design and engineering
experience, they look amazingly alot like another company we all know when
they first started out (Elecraft). Look at the schematics and read their
theory of operation before you judge the Juma products.

 

73

Dave KD1NA

 

 

David: Who are you going to believe? Me or your lying eyes? (;

While it is highly desirable to use a clean exciter, The only way a clean
exciter can make a bad amp better is to enclose the amp in a feedback loop
originating in the PA and terminating in the exciter. This can be done in a
rig such as the K3/100 where both the amp and exciter are in the same box
but is near impossible where you are dealing with 2 separate boxes.
Simply: If the Juma is broke, the KX3 can't fix it.

73

Fred, AE6QL