Section Ill. TECHNICAL PRINCIPLES OF OPERATION

TM 11-5815-238-20

1-9. DIFFERENCES BETWEEN MODELS

Refer to Operator's Manual TM 11-5815-238-10.

1-10. EQUIPMENT DATA

Refer to Operator's Manual TM 11-5815-238-10.

1-11. SAFETY, CARE AND HANDLING

Observe all WARNING, CAUTIONS and NOTES in this manual. This equipment can be extremely dangerous if these

instructions are not followed.

Section Ill. TECHNICAL PRINCIPLES OF OPERATION

1-12. GENERAL

Major mechanical components for high-level and low-level equipment are the same while their major electrical

components are different. The technical principles of operation for plain and lettered models of teletypewriter

reperforator-transmitters are the same.

1-13. SIGNALING CODE

In standard teletypewriter operation, the code for different characters always consists of five units of an equal length

of time. These units are called mark pulses and space pulses; the five-unit mark-and-space code group for the letter

X is given below.

Standard teletypewriter signals are transmitted by neutral and polar operation. In neutral operation, current flows

through a circuit in only one direction. Mark pulses are current pulses, space pulses are non-current pulses. In polar

operation, current flows through a circuit in both directions. Mark pulses are current pulses in one direction, space

pulses are current pulses in the opposite direction (opposite polarity).

High-level TT-76(*)/GGC units are designed to receive both neutral and polar pulses but are wired to send only

neutral pulses.

Low-level TT-699(*)/GGC units are designed to receive and transmit 6 volt polar pulses only.

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