[GreenKeys] Why and When 7.00 vs. 7.42 unit code?

[Don Robert House]

Bell System was all unit Code 7.42 for 5-level communications.  This  
was felt to be needed for an extra long stop pulse to minimize  
transmission problems on long telegraph loops.
The USN did whatever they could make work. Aboard ship there was no  
such thing as a long loop.
If the Navy Department needed to communicate over Bell facilities they  
would use the 7.42 unit code to increase the reliability factor.
Western Union and other companies that interconnect with overseas  
networks used 7.0 unit code.

The chart I sent and you posted shows which combinations were used.   
The facilities used for communications were the controlling factor in  
most cases.
This is explained in more detail in the Navy book NAVSHIPS  
0967-233-0010 PRINCIPLES OF TELEGRAPHY (Teletypewriter)
I am planning on unbinding and scanning an old Bell Publication on  
Telegraph transmission that is also an excellent source for answers.

AT&T charged more for the higher speeds as all of their networks were  
private line after a judge gave all of the switched teletypewriter  
service to Western Union.
The higher the speed the more frequent maintenance was required.  They  
also charged for the amount of time used.
Full Period service was 24/7/365 Half Period was 12 hours a day and  
Quarter Period was 8 hours a day.  I do not remember any Quarter  
Period machines.
Most of our machines and facilities were Full Period. We had a few  
Half Period that were turned on and off with Sangamo Time Switches.
Every Spring and Fall one of us had to go change the time on the clocks.

There were a few switched private line services for pipeline  
companies, airlines, etc.

73,
Don K9TTY




On 10 Mar 2014, at 7:09 AM, Nick England wrote:

OK, I understand 7.00 unit code means you can run a bit faster, but  
who used it in practice and in what circumstances?

  I understand WU was all 7.00 - is this right?

Looking at the Navy's list of TTY units, there were both 7.00 and 7.42  
unit machines galore - how was it decided what to use where? Were all  
on-line crypto machines 7.00 or some systems were 7.42 and some were  
7.00? Or what? What about Signal Corps gear?

Was there just a break and after July 17, 1958 all new Bell  
installations used 7.00 or whatever? Or was this decided on a case by  
case basis - and what was the basis?

Thanks for helping to reduce my confusement.
Nick England K4NYW
www.navy-radio.com
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