[Elecraft] [KPA500] Low Power Use Cases

[Edward R Cole]

Chris,

I cannot answer how well the KPA500 will run when driven 1 to 5w, but 
JT65 does NOT require a linear amp.  It runs the same as CW, only 
stepping in frequency (makes different tones in a SSB receiver), so 
one can use a class-C amp if they want to with JT65.

Therefore, there is no concern about intermod distortion (any more 
than if one ran CW).

How efficient the KPA100 runs when lightly driven is another topic 
which I cannot answer. It does reason that the heat sink should 
easily take care of the heat at 50w, if designed for operation at 
500w.  If the KPA500 runs in class-AB it will dissipate some minimum 
level without RF drive.  If it were class-A it would dissipate full 
power all the time.

I run my 8877 far into class-B so there is almost no idle current 
without drive.  In class-C it would be biased at cutoff.

One might measure the current draw without drive, but often much of 
this is attributed to digital control components that have nothing to 
do with dissipation of the finals.  Perhaps the Elecraft engineers 
have that number?

73, Ed - KL7UW

Date: Thu, 18 Jul 2013 15:08:14 -0700
From: Chris Johnson <ozy at ozy.us>
To: "elecraft at mailman.qth.net Reflector" <elecraft at mailman.qth.net>
Subject: [Elecraft] [KPA500] Low Power Use Cases
Message-ID: <B2A54E7D-2C09-488A-AF09-55F224798105 at ozy.us>
Content-Type: text/plain; charset=us-ascii

I love my KPA500.  I don't use it enough because of all the low power 
digital I do.   I was wondering if the quality of my signal would 
better if I let the KPA500 produce the output even if the wattage is 
50 or less watts.   If I drive it with 1 to 5 watts, it produces 10 
to 50 watts.   I like the thought of offloading the thermal load of 
my long JT65 & JT9 duty cycles onto the KPA rather than my main rig 
which is a Flex 6700.

Does the KPA500 make a much cleaner signal than the built in barefoot 
amp because its running at such a higher voltage?   I'm not too 
concerned about power efficiency comparisons, because we know its not 
more efficient doing it this way. :)

Thx

-Chris



73, Ed - KL7UW
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