Panel Controls. cont'd

Function

Control

applied to the synchronous winding of the motor causing the motor to

START-PHASE, switch (S3) (Facsimile

lock in at its normal operating speed. The receiving operator throws

T r a n s c e i v e r s TT-1D/TXC-1, TT-1E/

the START-PHASE switch to the PHASE position to energize the

TXC-1, and TT-1F.TXC-1 Only)-

phasing circuit of the receiving transceiver while the transmitting oper-

Continued

ator is sending phase pulses. When the relatively short phasing opera-

tion is completed, the machines remain Synchronized because both

drums are driven by motors running at the same speed.

Caution: The motor of Facsimile Transceiver TT-1D/TXC-1,

TT-1E/TXC-1, or TT-1F/TXC-1 is at synchronous speed only when

the 1,800-cycle tone can be heard from the motor laminations.

Used in the 30RPM position to provide half-speed operation of the record-

30RPM-60RPM

(motor

speed control)

ing drum when transmitting over long radio circuits under adverse re-

switch (S4) (fig. 138) (Facsimile Trans-

ceiving conditions, and in the 60RPM position for normal operation.

c e i v e r s TT-1D/TXC-1, TT-1E/TXC-1,

and TT-1F/TXC-1 only).

A calibrated potentiometer which adjusts the contrast range (difference

CONTRAST control (R45) - - - - - - - - - - - -

between minimum and maximum signal level of the transmitted signal)

by adjusting the magnitude of currents in the photocell bridge circuit.

This control is operated only by the transmitting operator, although

the setting he makes is determined partially by the request of the re-

ceiving operator. The dial on this control is numbered from 1 to 100,

and the ranges for transmitting positive and negative are indicated.

A dual potentiometer which serves to control the level of the signal han-

GAIN control (R59 and R60).. .

dled by the transceiver. It does not change the contrast range.

The front panel DB METER serves as a guide in setting GAIN and

DB METER (M1) . . . . . . . . . . . . . . . . . . . . .

CONTRAST controls. It is calibrated in db with reference to 0 power

level of 6 mw in 600 ohms. Line power levels are commonly expressed

in terms of dbm, decibels with reference to 0 power level of 1 mw in 600

ohms. The DB METER on this equipment does not register the true

line signal level in either db or dbm. When the facsimile transceiver

selector switch is at TRANSMIT and the DB METER indicates plus

2 db, the resultant power dissipated in a 600-ohm resistive load con-

nected across the LINE binding posts is 1 mw (.78 volt), representing

the standard 0 dbm reference. When the facsimile transceiver is re-

ceiving, there is no fixed relationship between line power and db power

and DB METER reading, because meter readings depend on the setting

of the GAIN control. In paragraph 5, input and output signal levels

for the transceiver are expressed in true line dbm. Elsewhere in this

manual, however, the term db is used merely to express the relative

level readings of the DB METER, not to indicate line levels in dbm.

Used for setting the transmitting contrast (wedge) range.

This meter may be temporarily disconnected from the circuit, and may be

used to measure dbm (at 0 dbm =1 mw into 600 ohms) directly, provid-

ing 8 db is added to the meter reading when so used.

Provides a means for turning off the motor when the selector switch is in

MOTOR ON-MOTOR OFF switch. (Added

the STANDBY position.

on Facsimile Transceiver TT-1/TXC-1

only by MWO SIG 11-2258-1).

Permits connecting an xternal loudspeak to the transceiver so that the

S P E A K E R jack. (Added on Facsimile

maximum and minimum signals for setting contrast will be audible to

Transceiver TT-1/TXC-1 by MWO SIG

the receiving operator.

1122581).

Provides continuous check on regulated

250-volt supply.

meter (M3) (fig. 138). . . . . .

Connected in series with motor voltage supply for setting proper motor

MOTOR CURRENT meter (M2) -- ----

current.

Note. Meters M2 and M3 were added to Facsimile Transceivers TT-1/TXC-1 and TT-1A/

TXC-1 by MWO SIG 11-2258-2.