GRS SyncroScan cTc code equipment:

G-R-S Syncroscan is a coded communication system for control and indication of remote functions.
These functions may be grouped at one location, or they may be situated at a large number of locations, widely spaced.
The system, therefore, may be used to handle one large interlocking, a group of interlockings,
or a section of centralized traffic control.

G-R-S Syncroscan is comprised of two seperate systems, one for controls, the other for indications,
operating independently of each other.
An all-relay system is used for the transmission of controls from the control office to the field locations.
A continuously scanning electronic system is used to bring in indications from the field stations.


The relay control system makes use of relays utilizing the
free swings of mechanical oscillators - one at the control
office and the other at the field locations - to create
steps of a control cycle.

These steps are equal units of time in the cycle, information
being conveyed by the polarity of energy (or by frequency
shift, if carrier is used for controls) on the line during
each of the steps.
In the transmission of controls, a code cycle of 15 steps
is used. The cycle time is 1-1/2 seconds. Thirteen of the
steps handle the actual controls, each step being able to
operate a two-position function, such as a switch or a
single-direction signal.

Generally, the first few steps are used to designate a
"station", i.e., a particular group of controls, usually at
a common location, such as those for a siding-end in cTc,
or a portion of the switches or signals at an interlocking.

For cTc, the 13 control steps may be assigned by varying
combinations of stations plus controls. A typical
arrangement might use 6 steps for station selection and
7 for controls. This would provide capacity for 64
stations with 7 controls per station.

Indication System Office Storage Unit

The electronic indication system operates on independent
carrier links between the control office and field stations.
The scanning of indications is accomplished by sending
pulses from the office via carrier link to the various
field stations, checking the field functions to be indicated,
and returning these pulses to the office on a different
carrier link.

It is possible to operate an entire Syncroscan system by
carrier, using one frequency for controls and two for
indications. In such an arrangement, no physical line is
Indication System Field Stepper Unit
The indication capacity of Syncroscan is large and very
flexible. The positions of all field functions are scanned
in sequence and indicated at the control office. As soon
as a scanning cycle is completed, another follows
immediately and automatically.

Since the scanning rate is 100 indications per second, a
system having 400 indications, for example, checks each
indication every 4 seconds.
When a field change occurs in an installation of this size,
the indication change occurs at any time from immediately
after to four seconds after the field change, depending
upon the time of the change with respect to the scanning
cycle. In no case would the interval exceed four seconds.

Indication System Office Carrier Unit
Both the office and field equipment are linked to the
line via carrier receivers and transmitters, through
filters. Frequency-shift carrier equipment is used.

Each transmitter transmits on one or two closely spaced
frequencies. Each receiver detects which of the two
frequencies has been transmitted by its companion

The carrier link between the office and the field operates
in a 1-kilocycle band centered at 6500 cycles-per-second.

The carrier link from the field to the office operates
in a 1-kilocycle band centered at 11000 cycles-per-second.
From: "G-R-S Sycnroscan, For cTc and remote control" - Pamphlet 876 - October, 1955.