[GreenKeys] Re: M20-RO

[Sheldon Daitch]

David,

Thanks for the listing.

These do match my chart for the 16 channel tone pack
that was used with the Tele-Signal manufactured 
FCC-19 and FCC 25 systems, which, per my spec information,
was rated up to 100 wpm.

In the thinking out loud department, I wonder if anyone
can confirm that the Lenkurt 25A system also used
the same channel pairs, per David's chart below.

I was looking at another piece of equipment, the 
tone keyer and demodulation equipment marketed with
the RCA SSB-R3 ISB systems, and this line of tone
equipment would put 19 TTY signals on a VF grade circuit,
42 Hz shift, channels on 170 Hz spacing, with the
channel center frequencies as:

  255    425    595    765    935    1105   1275

  1445   1615   1785   1955   2125   2295

  2465   2635   2805   2975   3145   3315

I never saw this equipment, only info from the 
RCA receiver manual.  As with a lot of RCA's 
equipment, it was relabeled gear from another
manufacturer.  I can't determine yet, who made
this VFTG equipment, Allied Signal has latched
in my mind, but I can't confirm it.

(Singer/Tele-Signal made the FCC-19s that I
saw.)

Sheldon


David Ross wrote:
> 
> RTTY folks -
> 
>   There is precious little teletype MUX stuff on HF lately, most all
> data traffic has migrated up to satellites.  Lately is it just a fast
> bitstream sent via satellite, no need for audio tones at all...
> 
>   A common teletype MUX format in the 1960s & 1970s had 16 tone pairs in
> a 3 KC audio passband.  The scheme was intended to accommodate 16
> simultaneous 75 baud bitstreams.  Each tone pair used 85 CPS shift,
> center freqs were 170 CPS apart and started at 425 CPS -  tones are like
> this:
> 
>  382.5 &  467.5
>  552.5 &  637.5
>  772.5 &  807.5
>  892.5 &  977.5
> 1062.5 & 1147.5
> 1232.5 & 1317.5
> 1402.5 & 1487.5
> 1572.5 & 1657.5
> 1742.5 & 1827.5
> 1912.5 & 1997.5
> 2082.5 & 2167.5
> 2252.5 & 2337.5
> 2422.5 & 2507.5
> 2592.5 & 2677.5
> 2762.5 & 2847.5
> 2932.5 & 3017.5
> 
>   In the '60s, both Collins & TMC built HF radios with filters
> compatible with this format -  the radios used special IF filters with
> well-defined widths & passband flatness & group delay.
>   Varying delays across the filter's passband were critical, since one
> optional MUX configuration had the 16 separate channels set up as 8
> dual-diversity channels.  Between two diversity channels analog voting
> was used, and the scheme worked best if the incoming sigs were exactly
> in sync.
> 
>   The CCITT spec that defines this old-timey MUX format also specifies
> four sidebands called A2, A1, B1, & B2 -  if you see a radio with
> sidebands named like this then it probably uses these fancy superflat
> filters...
> 
>  -  A2 is the LSB of a suppressed carrier 6.29 KCs
>     above the dial freq.
>  -  A1 is plainjane USB
>  -  B1 is plainjane LSB
>  -  B2 is the USB of a suppressed carrier 6.29 KCs
>     below the dial freq
> 
> Dave Ross    N7EPI    ross@hypertools.com
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