[GreenKeys] Fw: Military RATT mark high/low change

[Sheldon Daitch]

   ----- Forwarded Message ----- From: Sheldon Daitch <sheldondaitch at yahoo.com>To: Duncan Brown <duncanancy at earthlink.net>Sent: Wednesday, November 23, 2022 at 05:00:49 AM ESTSubject: Re: [GreenKeys] Military RATT mark high/low change
  The RTTY system was run at the VOA C Site location.    The machines were M28s from pretty day onein 1962 or so until about 1987 or thereabouts, when we replaced the M28s with Extel units.
I am going from memory, but I remember we had four M28s in the comm room, three were ASRs and onewas a KSR, all floor models.
Looking left to right along that wall, was a Telex machine, most probably M32, five level with a tape punch and tape reader.
Next was an M28ASR which was our Greenville to Washington system.  I am thinking it punched tape forthe outgoing RTTY message feed the next morning.  Our HF RTTY feed was about 3.5 hours, 30 minutes to Liberia,Munich, Kavala, Rhodes and Tangier and about 15 minutes with Botswana.
That circuit from Washington had a mix of traffic, so the evening shift operator would take the various messagesand punch a master send tape, one for each station, so the morning TTY operator did not have to determine whattraffic needed to be in the morning outgoing schedule.
I think we used the far right M28ASR for the outgoing traffic, using the TD on the M28ASR for sending the type, and theconfusing part for me is that the machine read that tape, but the M28ASR also punched the tape for the incoming trafficfrom the overseas stations.   
We used FAXFAX for the start code and NNNN to end, but as I recall only FAX was necessary to start the type puncherand NNN would stop.
We also used chadless tape, so when we got the end of a message, we'd pull the tape out, by a foot or so, to separatethe incoming messages, for sending to Washington later in the tape.
On a good propagation day, we'd have little to clean up.  On a bad propagation day, we'd have to have the overseas stationsend traffic multiple times.  Every now and then Greenville would have to repeat messages, but considering our transmittershad more power than the overseas stations, it wasn't that often.
Writing this reminded me of a story in the conversion to the Extel units.   Billy-Bob Cope had fixed up an electronic keyer which alternated R and Y but with maybe ten to twenty rubouts, so that we could keep the transmit circuit off idle,but not fill up the far end with rolls of RYs.    When we converted to the Extel units, we found that this test keyer circuitwould fill up the transmit memory on the Extels so, we have to bypass the Extel for the test "tape" idle circuit keyer.
When I was at Greenville, we were using a Northern Radio Type 153 keyer, probably the Model 1 and for the tonedecoder, the Type 174 Model 1.
73
Sheldon



    On Tuesday, November 22, 2022 at 05:43:37 PM EST, Duncan Brown <duncanancy at earthlink.net> wrote:  
 
   Sheldon,
 
 Was the VOA TTY machine a M28?  KSR or ASR? Floor model?  Was it located in the main control room, or in another room?
 
 I'm wondering if I should add a M28 to the AWA Museum's VOA control room.
 
 Thanks,
 
 Duncan Brown, K2OEQ
 USASA    31J30
 
 i-Telex: 212503
 
 Antique Wireless Assoc. Museum,
   Asst. Curator, Commercial Equipment
 (also chief TTY op & repairman)
 
 www.antiquewireless.org
 
 
 On 21-Nov-22 22:12, Sheldon Daitch via GreenKeys wrote:
  
  Deflecting this a bit to non-military use, when Voice of America was running the RTTY schedules out of Greenville to the stations in Europe and Africa, we used AFSK on the ISB transmitters.   I don't think I have any access to any of the old schedules to back me up on this, but I don't think we cared if the AFSK audio was on USB or LSB, simply because we demodulated the RF signal back to audio, so the upper/lower tones were always correct to feed to the AFSK tone convertors. 
  One point which might have been valid for some transmitters, the upper tone being at the end of the audio bandpass of the channel is that all of our exciters had six kHz channels, for program audio, so there was no issue with any high frequency roll off affecting the higher of the two tones. 
  We also used two tone pairs, and I have no idea what tone pairs were used, but  both tone pairs were keyed simultaneously (and at the same time), and the tone convertors on the receive side used the two sets of tones in a diversity process, which helped a bit in achieving good copy. 
  Greenville was still using Northern Radio tone keyers and tone convertors when I left in 1989, and I don't know if there were any changes to when we moved from the RTTY circuits to the email based communications.    
  Too far back for some of the memory cells. 
  73 
  Sheldon 
   
 
 
     
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