Speech processing

[David Windisch]

CONTENTS DELETED

The author has deleted this message.

[G3VVT]

 
In a message dated 04/03/05 11:00:07 GMT Standard Time,  [hidden email]
writes:

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



---------------------------------------------------
 
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
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[N8LP]

Yes, that's the one I had and was referring to... it worked great. I
knew it was Com-something ;-) Sounds like there are already a couple of
knockoffs out there.

Larry N8LP



David J Windisch wrote:

> Hi, all concerned:
>
> I have an old Comdel in-mic-line r-f clipper, which uses fewer than
> 100 discrete parts on a 4X6in board.
>
> What the device does is to heterodyne baseband audio to vlf, put it
> through a USB filter, limit it, lowpass-filter it, and heterodyne it
> to baseband. Inband distortion products are kept down this way.
>
> If there's enough interest, it could be resurrected by retrofitting
> with newer parts, eg, inductors other than telco toroids ;o) and kitted.
>
> If anyone knows of contra indications, do please step forward.  I've
> done a cursory search for Comdel and its successors and found nothing
> except old ads and a review in June 1968 HAM RADIO magazine (it sure
> was a pleasure to reread some Jim Fisk).
>
> I do recall reading that the unwary occasionally fried amps which
> couldn't stand the increase in average power.  Caveat user.
>
> If anyone wants to hear what the thing sounds like, I could get on
> 160-10M ssb once I figure out the internal mic connections to my to
> K2/100. Fingertalk is much easier, for me in any case.
>
> 73, Dave, N3HE
>
>
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[N8LP]

This is one for Eric to weigh in on, but with proper in/out routing
between transmit and receive, I wonder if it wouldn be possible to come
up with an algorithm to make the KDSP2 work as an rf clipper/filter in
transmit with baseband audio output? Of course, the settling time
between T/R might well be a problem.

Larry N8LP



[hidden email] wrote:

>
>In a message dated 04/03/05 11:00:07 GMT Standard Time,  [hidden email]
>writes:
>
>I have  an old Comdel in-mic-line r-f clipper, which uses fewer than 100
>discrete  parts on a 4X6in board.
>
>
>
>---------------------------------------------------
>
>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
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>
>  
>

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[VR2BrettGraham]

There were a number of external RF speech processor products
available in the early 80s.  I can't find the schematic for my Kenpro
KP-601, but popping the cover I see something potentially
home-brewable (all this discussion drove me to find it, as after
changing compression ratios of the KSB2's compressor, it still
doesn't sound like I would like it to).

This one could turn a RF processor-less rig into something
that sounds like a TS-830S with a D-104 - clean, punchy
audio - and change the peak-to-average ratio enough that
I once baked the paint off the cabinet of an amplifier.

Not recommended for audiophiles or those who are interested
in more casual operation.

73, VR2BrettGraham

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