[Elecraft] Speech Processors

[George, W5YR]

Many thanks, Eric, for the words of comfort on the K2 finals.

I did not intend to give the impression that I could hardly wait to
hook up one of my processors and thereby "greatly enhance" the K2 SSB
performance. Thus far, my SSB operation has perhaps lasted 5 minutes
and that was during some checkout testing. As far as I could tell at
the time, monitoring on another K2, the first level of compression
worked well for my voice and the MH-2 microphone.

My interest in my original posting was to alert those unfamiliar with
speech processing that it can place additional demand on the final
amp. Since I cannot recall seeing a duty cycle spec on the K2, I took
the conservative view that the finals could probably stand normal CW
and SSB operation with an adequate safety factor, but could not
necessarily stand up to a 6 dB increase in average power.

Also I was unaware that you are already employing a form of r-f
clipping and filtering in the balanced modulator - I wonder if you
have an estimate of the increased average power level obtained in that
manner?

"In the interests of science" I might see how the Comdel/K2
combination works out, judging the output both by monitor receiver and
scope examination of the r-f output envelope with two-tone testing,
etc. With any processed speech, the final arbiter is the tradeoff
between distortion and increases in intelligibility and average power
levels.

Thanks for the information, Eric.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489  IC-765 #2349 IC-756 PRO  #2121 IC-756 PRO2 #3235


----- Original Message -----
From: "Eric Swartz WA6HHQ - Elecraft" <eric@elecraft.com>
To: "George, W5YR" <w5yr@att.net>
Cc: "Elecraft List" <elecraft@mailman.qth.net>; "Julian (G4ILO)"
<g4ilo@qsl.net>
Sent: Monday, January 27, 2003 12:57 PM
Subject: Re: [Elecraft] Speech Processors


> The finals in both the K2 and K2/100 are certainly 'up to the
strain' :^).
>
> We designed them to handle way more than you will normally hit them
with in a
> processed SSB conversation. In the case of the K2/100 the finals can
handle a
> significantly higher temperature than we let them go to in firmware.
The
> heatsink and PAs are Ok even when the heatsink is almost too hot to
touch. At
> that point we still have a 50 degree safety overhead on the
transistors and
> will reduce power automatically before we get much closer to that
point. I've
> never seen that happen in normal or contest operation.
>
> When the K2's speech compressor is turned on we actually get some
additional
> RF compression by slightly overdriving the '602 balanced modulator
(on
> purpose). The resulting out of band IMD is filtered out by the SSB
filter,
> resulting in our characteristic punchy SSB sound. I'd expect little
> improvement (and a lot more distortion) from any additional
processing.
>
> 73, Eric  WA6HHQ
> Elecraft