[Elecraft] Re: Speech Processors

[Ignacy (NO9E)]

As Eric writes, K2 does some speech processing by compression within 
602A, especially on 10m. This is especially visible with new firmware 
that by default limits 10m to 10W, which brings K2 to within ALC range. 
However, average power on SSB seems to drop 2-3 times simply because 
average power is lower. Increasing the power to 12 W helps with no 
noticeable distortions. Should K2 be modified to allow some overdriving 
602 on all bands?

Higher end Kenwoods have excellent RF speech processors. At high level
of processing, my TS-850 shows an average power of 40% of PEP without
objectionable distortions (but higher ambient noise). Without the
processor, the average power is about 5%. On the air, 95% hams prefer
TS-850 with processor on and give 2-3 S better reports. My K2 in linear
stage shows average power of about 15% of PEP. Thus a good processor
could increase average power by 2.5 and slightly reduce distortions.

Designing good RF speech processor is not easy. It requires flat
filters, sharp clipping (hard to do with diodes back to back), enough
gain so that ALC works always, good ALC constants, and linear PA.

DF4ZS (http://jwm.de/afu/index0.htm) makes small RF processors that fit
into a microphone. I tried to homebrew mine 
(http://www.eham.net/articles/3179). In FT-100, I regularly got 2S
better reports. Still, average power was 25% of PEP due to imperfect
clipping, and the signal was narrow-sounding due to uneven filters.

73,
Ignacy