not included in the following list. A description of each
date a wide range of data rates to produce a single
circuit follows in the paragraph indicated.
serial stream of information, with its associated tim-
(1) Two-wire voice user with 20 Hertz signalling
j. Pulse Code Modulation Equipment (PCM). The
(para c below).
(2) Two-wire voice user with loop signalling (para
pulse axle modulation equipment normally accepts the
analog signal (the modulating signal) and samples it at
(3) Two-wire voice user with E&M signalling (para
a predetermined rate. The sample is then quantized
and coded so that each element of information consists
(4) Two-wire voice user with standard integral sig-
of differing numbers of pulses (marks and spaces).
This equipment generally uses an eight bit sample
nalling (para f below).
(6) Four-wire user with standard integral signal-
ling (para g below).
(6) Four-wire user with 20 Hertz signalling (para h
(1) Digital Modems (VF). This is a modem which is
used to convert direct current signals appearing on the
(7) Four-wire user with loop signalling (para i be-
digital patch bay to the analog form for appearance on
the equal level patch bay. This equipment requires a
(8) Four-wire data user cable to TCF (para j be-
nominal bandwidth of 4 kHz
(2) Special Digital Modems (Group). Input to this
(9) Two-wire or four-wire voice user using non-
modem is in digital form from the digital patch bay.
standard in-band signalling (nonstandard signalling
Its output is analog form and appears on the group
unit at user terminal) (para k below).
patch bay in the standard frequency division multi-
(10) Four-wire user with DX signalling (para l be-
(3) Special Modem (Supergroup). Input to this mo-
dem is in digital form from the wideband user/switch
(11) Four-wire PBX trunk to AUTOVON (PBX
cable to TCF) (para m below).
or TDM. Its output in analog form appears on the su-
pergroup portion of the coaxial patch bay in the stand-
(12) Four-wire data user with DX signalling (para
ard FDM supergroup frequency bandwidth of 312 to
(13) Two-wire PBX cable access line (two to four
wire conversion at PBX) to local AUTOVON switch
2-17. Voice Frequency Circuits
(para o below).
a. General. All voice frequency (vf) users including
(14) Four-wire AUTOVON subscriber telephone
AUTOVON, AUTODIN, and AUTOSEVOCOM
cable to TCF (loop resistance less than 700 ohms) (para
switches, communications centers, PABX's, local
switchboards and tactical multiplex equipment access
(15) Four-wire AUTOVON circuit (remote two-
the TCF by way of the Primary Patch Bay. Four-wire
wire PBX subscribers) (para q below).
fixed station multiplex equipment utilizing 2600
(16) Four-wire AUTOVON special grade circuits
Hertz signaling access the TCF by way of the Equal
(AUTOVON subscribers (data) and inter-switch
Level Patch Bay. All conditioning and signalling
trunks) (para r below).
equipment required to achieve compatibility between
(17) Four-wire AUTOVON voice grade circuits
users and the transmission media is electrically con-
(para s below).
nected between the Equal Level Patch Bay and the Pri-
(18) Voice and telegraph users connected to High
mary Patch Bay. The Primary Patch Bay terminates 2,
Frequency radio transmission media (pars t below).
4, 6, or 8 wire user circuits. The Equal Level Patch Bay
(19) Four-wire voice frequency carrier telegraph
serves at the principal point of interface and restora-
(para u below).
tion in the Technical Control Facility. Circuits appear-
(20) Fixed station multiplex interconnection (para
ing at the Equal Level Patch Bay appear as 4-wire bal-
anced pair circuits (AUTOVON switch circuits having
(21) Non-DCS multiplexer user to DCS user on
Pilot Make Busy capability appear as five-wire cir-
base, or using DCS transmission media (para w below).
cuits). The Equal Level Patch Bay is the zero (0) test
(22) Four-wire entrance toll cable (para x below).
level point in the station, that is, OdBr send and re-
(23) Four-wire connections to High Frequency ra-
ceive. DCS standard supervisory signals appear as
dio systems (para y below).
2600 Hertz tones at the Equal Level Patch Bay.
c. Two- Wire Voice User With 20 Hertz Signalling
b. Circuit Descriptions. The following is a list of the
). The users for this circuit are either a
various types of voice frequency circuits which may be
two-wire switchboard or an individual two-wire user
commonly found appearing in the Technical Control
using 20 Hertz ringing source. This circuit provides
Facility. A TCF may service other circuits which are
echo suppression and control in order to minimize