Back a while ago I got my foot firmly into my mouth re 20/1000 ringing
induction on the POTS telephone network in this age. My apology to all.
20/1000 was used extensively in the old analogue network, the toll
transmission part of the system. It was also used extensively in private
line systems such as air traffic control and weather circuits where the line
was monitored full time by a speaker system. The 20 Hz rang the bells, the
1000 hz woke up those who were audio monitoring. When you lifted the
handset the speaker was cut off, so if the handset was sitting on the desk
the bells rang, or the 1000 Hz would wake the dead through the speaker.
The ringing generators, a number of types, but in this case were made by the
Holtzer Cabot
Co. of Boston and examples are on display of the 20/1000 generators in a
number of museums, mainly in the USA.
Why I was convinced that this was used on the POTS network I am not sure. I
have now checked
a number of line cards used in both ESS and DMS switches and find that it is
not even an option anymore.
Again my apology to all.
Larry
VA3LK
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