[Elecraft] Re: Speech Processors

Thu Jan 30 00:48:04 2003

If you are creative, you can recalculate the compression characteristics by
downloading the datasheet for the chip and changing the resistors. You could
even change the resistors to variable.  I think the chip (as designed and
implemented In the k2) is set at the lower end of the compression curve.
You could also acquire one of the chips and mount it in a mic with variable
gain and compression.  You would then bypass the chip in the k2.

If you take a look at the chip datasheet I think you will find that it is
quite capable of compressing (and distorting) audio with resulting increase
in average power with the best of them.  I like the chip and the
implementation in the k2.

Unless you are using a storage scope or measuring the heat from a dummy load
it is very difficult to ascertain the "average" PEP of an SSB signal.  Logic
follows that it the input signal is being compressed then the output
peak/average ratio is changing.

Audio only - obviously.

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of George, W5YR
Sent: Wednesday, January 29, 2003 9:28 PM
To: [email protected]; VR2BrettGraham
Subject: Re: [Elecraft] Re: Speech Processors

Brett, not that I am in any position to defend or justify the K2
compressor design, but  let me say that what they have done is simple,
inexpensive and remarkably effective for what it is intended: make the
SSB signal from the K2 have a "punchy" sound. From what I can see, the
design intent was NOT to provide much if any increase in average r-f
power output, which as you observe is the case.

Also, we need to keep in mind that what can be done in the audio
domain is comparatively limited to what can be done with "true" r-f
processing. The K2 is an elegant but simple analog system. My PROs,
for example, are complex IF DSP systems with highly effective
r-f processing available.

Based upon the assurance by Eric that the K2 finals are up to a
reasonable increase in average power, I may drag out the Comdel  and
Vomax and see how the K2 sounds and behaves with a few dB of r-f
processing applied. But, I can almost predict with certainty that I
will not use it on the air even if the tests reveal some improvement
in performance. The Comdel is nearly as large as the K2, uses quite a
bit of power (that 6 dB has to come from somewhere! - just joking) and
I really doubt that my limited use of SSB with the K2 would justify
the trouble. As you have probably surmised, most of my operation is
QRP CW.

Back in the early 70's I designed and built a true r-f clipper/filter
for the Heathkit SB-401 transmitter which I ran into an SB-220 at a
full gallon. With at least 10 dB of clipping - probably closer to 15
dB but I had no decent instrumentation back then - the poor old SB-220
plate meter just about hung at the 90%-key down level while I was
talking. I received many reports from the East Coast area that I was
one of the loudest W5's on the band. Many times, I was reported to be
louder with the SB-401 alone and the processing on that with the KW
and no processing.

So, I know about this paint-baking business!  <:}

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: "VR2BrettGraham" <[email protected]>
To: <[email protected]>
Sent: Wednesday, January 29, 2003 10:48 PM
Subject: Re: [Elecraft] Re: Speech Processors

> My initial reaction to trying the K2's speech processor was that it
didn't seem
> to make much difference to bringing up the average power.
>
> I have an external RF processor (JA-made, I believe) that almost
baked the
> paint
> off an amp at 7RM one year as it really brings up the average
power - something
> to try later.
>
> NO9E is right - a good RF processor isn't easy to do.  I think what
> Elecraft has
> done is a bit pedestrian by comparison.
>
> 73, VR2BrettGraham
>
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