[Elecraft] K3 - contesters want to know

[Lyle Johnson]

> Phone contesters want to know about the speech processor...
> 
> How does the DSP I.F. speech processor compare to a true RF processor

RF processors that I am aware of work at IF, same as the K3.

Essentially you create an SSB signal, using AGC/compression to keep the 
average signal level reasonably constant.  You then apply additional 
gain tot he IF SSB signal which drives the clipper.  This gives you "RF 
clipping" with an adjustable amount of clipping.  You then re-filter the 
resulting signal and convert it to the output frequency.

Thus, the K3 has a true RF speech processor.

It also has audio compression ("ALC") and an 8-band Tx EQ to tailor the 
overall response.

Finally, you can monitor the result of all this as the SSB voice monitor 
samples the IF output of the DSP so you can hear what the station at the 
other end will hear (except for the QRM, QRN and QSB of course - we 
haven't added an atmospheric or contest simulator yet ;-)

> versus 
> the audio compressor circuit in the K2?

Compressors (the K3 has that option, too) generally provide fairly low 
distortion and limited improvement in average ("talk") power.  They 
can;t provide the punch you get with RF clipping due to the IMD and 
harmonic products.  Audio harmonic products fall in the audio passband; 
RF clipping harmonics are outside the passband of interest.

For an excellent writeup, see QST for July, 1967 "R.F. Clippers for SSB" 
by William Sabin, W0IYH.

73,

Lyle KK7P