|34 Years of the Digest ... founded August 21, 1981|
|Copyright © 2016 E. William Horne. All Rights Reserved.|
The Telecom Digest for Sun, 15 May 2016
Volume 35 : Issue 78 : "text" format
Table of contents|
|An Unneighborly Building That Hums With Lifesaving Capacity||
|Re: Switchboard BD-72 connections to the PSTN||Scott Dorsey|
Date: Fri, 13 May 2016 10:18:40 -0400
From: Monty Solomon <firstname.lastname@example.org>
Subject: An Unneighborly Building That Hums With Lifesaving Capacity
By David W. Dunlap
From its extraterrestrial presence to its security-state name, PSAC II, New
York's new emergency answering center, is not neighborly. But you'll be
glad it's there.
Yet it may save your life someday.
PSAC II is New York City's second Public Safety Answering Center,
where more than 11 million emergency 911 calls are taken by the Police
and Fire Departments each year. Beginning next month, it is to
supplement PSAC I at 11 MetroTech Center in Downtown Brooklyn.
Date: 14 May 2016 10:07:55 -0400
From: email@example.com (Scott Dorsey)
Subject: Re: Switchboard BD-72 connections to the PSTN
In article <firstname.lastname@example.org>, Bill Horne <bill@horneQRM.net>
>If you're familiar with the Army surplus switchboard type BD-72, I need
>I know someone who wants to connect one of these switchboards to the
>PSTN; i.e., to have a dial tone on one of the lines instead of a
That's a local battery switchboard, it will require extensive modification
to use on a common battery system.
It has drops on the switchboard, so when people crank their phones, it
energizes the drops and makes it clear to the operator that someone wants
service. Then the operator plugs a passive headset into the jack for
that line and the local battery in the telephone provides talk power for
the operator to ask what service the subscriber wants. The operator plugs
his passive headset into the jack for the other subscriber and cranks
the magneto to ring the second phone. Then when the other party answers,
he connects both.
One of those two subscribers may be another switchboard connected to other
subscribers, possibly through a relay-and-transformer arrangement to graft
the field telephone network to a commercial local battery exchange.
If the fellow wants to use the switchboard with common battery phones on
the PSTN, he's going to have to figure out three things:
1. how to provide -48V talk power for the operator to talk to the
2. how to provide ringing voltage for the subscriber phone to signal
3. how to provide signalling so the operator can signal the PSTN to dial
the call, and a facility to keep the line locked between the time the
operator disconnects his headset from the PSTN to the time the operator
plugs the subscriber into the PSTN.
This is going to mean pretty extensive reworking of the switchboard. A good
introduction to how field telephone systems are meant to be operated can be
seen in Army TM 11-330, and a good introduction to the principles of operation
of common and local battery systems can be found in TM 11-498.
There is another TM called "Handbook for Wiremen" which is about deployment
and configuration of large field telephone networks as well as how to
document networks, but I can't remember the TM number offhand.
>Please tell me if you can do it, or know someone who has already done
>it. You may contact me offline if you prefer.
I wouldn't be surprised if some poor Frenchman did it after the war,
"C'est un Nagra. C'est suisse, et tres, tres precis."
End of telecom Digest Sun, 15 May 2016