[GreenKeys] A first look inside the Pasco 35 ASR

[Jim Haynes]

On Sat, 8 Aug 2015, Pete Lancashire wrote:

> They mystery of "REPEAT BID / SINGLE BID" is still unsolved
> 
We know in general that term applies to systems in which there is
a line controller that polls the stations, and those that have traffic
to send indicate it with a "bid".

The part with all the electronics is no doubt an "electronic stunt box"
used to recognize codes to turn the printing on and off and to bid and
respond to polling.  So that on a multistation line the printer only
copies messages intended for that station.

I'd be interested to know in that package what sort of thing exists for
programming it in the field for the codes it is supposed to recognize.

Some history: in ancient (Model 15) times there was a separate machine
called a SOTUS that could recognize characters and sequences of characters
that came over the line.  These sequences are typically codes to allow
the printer to print or not print on a multistation line and to recognize
polling and start the tape transmitter if there is traffic to send.

In the Model 28 era this activity was performed by the printer stunt box,
so a separate machine was unnecessary.  The CAA/FAA was a big user of
this capability; but it was also used in other private line message
systems.  In this kind of service the printer often made a "busy sound"
as it was reading traffic on the multistation line with printing
suppressed.

With Model 35 the same kind of stuntbox activity was possible.  Some
customers objected to the noise made by the printers when not printing.
I guess this didn't bother the FAA since they always had several printers
running next to each other; but a business office might have only a
single machine, and the office people were bothered by the machine
making noises when it was not printing.  So a silent "electronic stunt
box" was wanted; and in the era of cheap integrated circuits it was pretty
easy to implement.