[Elecraft] Speech processing

[G3VVT at aol.com]

In a message dated 04/03/05 11:00:07 GMT Standard Time,  davidjw at cinci.rr.com 
writes:

I have  an old Comdel in-mic-line r-f clipper, which uses fewer than 100 
discrete  parts on a 4X6in board.



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I have one of the Datong D75 RF speech processors since about 1980 (25  
years).
 
The leaflet that came with it shows it as being derived from earlier  
products, the RFC and the automatic model the ASP, though not sure when these  were 
first on the market. By the time the D75 was introduced the circuitry had  been 
reduced to 7 IC and 2 transistors. Uses the phasing method to generate an  
SSB signal at 60kHz then clipped before demodulation back to audio. Draws 9mA  
from a small PP3/6F22 internal 9V battery or can be externally powered from  
the radio which is what I did with a Yaesu FT707 used at one time.
 
It worked well though the resultant audio quality was not for local usage  at 
higher levels of clipping!
 
What does what inside the box is a mystery as Datong are infamous for  not 
releasing schematics, a policy carried through to this day I found out when  
trying to obtain circuit information of their DF1 FM RF direction finding  
system. I have one with a missing head unit and need to get into operation for  
tracking local morons on the repeaters. A request to Datong who are now in the  
professional RF surveillance field after pulling out from the amateur market for 
 help and schematic information led to a polite, but firm refusal.
 
The main station HF transmitter in use at this end the JRC NSD-515 (1982  
vintage) uses RF clipping in the IF chain with 2 filters cascaded, one  either 
side of the TA7302 clipper IC at 8.7MHz. This works very well with  resultant 
audio quality good enough to leave it in circuit at all times for SSB  and just 
varying the amount of clipping to suit the occasion. A great pity that  the K2 
does not use something similar with the KSB2, but with available space at  a 
premium, would guess that this would be rather difficult to fit in.
 
Bob, G3VVT