motor amplifier driver stage of the trans-
ceiver for test purposes or for supplying
Several distances can be obtained over voice
an external signal to the motor amplifier.
wire line circuits for a given line loss. The max-
The drum of Facsimile Transceivers
imum distance that can be covered for a given
T T - 1 D / T X C - 1 , TT-1E/TXC-1, and
line loss generally depends on the type of wire line
TT-1F/TXC-1 can be operated at any
facility used. The wire circuits used to transmit
speed from 30 revolutions per minute
facsimile signals must be of better quality than
(rpm) to approximately 100 rpm by
those suitable for voice transmission. The method
connecting an external signal of approx-
of connection used depends on the. type of circuit,
imately 26 to 35 volts root mean square
the loss and faults in the circuit, type of terminal
(rms), with a source impedance of 20,000
equipment used, and the frequency characteristics
ohms or less, to the sleeve and ring of a
of the line.
plug and inserting it into MOTOR JACK
J6. It may be necessary to ground the
Transceiver TT-1(*)/TXC-1 is an am 1,800-cps
external generator to Facsimile Trans-
carrier, and the circuit used is capable of passing
ceiver TT-1D/TXC-1, TT-1E/TXC-1,
both the upper and lower sideband frequencies,
or TT-1F/TXC-1 for satisfactory op-
900 to 2,700 cps, as flat as possible for satisfactory
eration of the motor circuit. The motor
reproduction. The impedances of all the circuits
speed control switch, S4 (30 to 60 rpm),
along the line should be matched to avoid re-
should be in the 60RPM position for
flections. When the circuit distance is long, the
external signal frequencies above 1,200
received signal is reflected back to the sending
cps, and in the 30RPM position for fre-
station and is reflected again over the line to the
quencies below 1,200 cps.
receiving station. This causes two images to
(8) ( ND post. Directly below the LINE
appear on the received copy. Echo suppressors,
binding posts is a GND post connected
which allow transmission in only one direction,
to the frame of the transceiver.
may be used in the circuit to overcome these effects.
On short high-speed circuits, the echoes produce
d. Mounting Dust Removal Blower Unit. Place
no undesirable effects.
the dust removal blower unit on the right-hand
b. It is important that the signal level at the
end of the shelf of Table MT-252(*)/TXC-1 as
receiving station be constant, especially when
shown in figure 2. Be sure that the blower unit
receiving photographic copy, since instantaneous
is resting firmly on the shelf and against the cross
changes as small as db in signal level will cause
brace before tightening the thumbscrews located
a noticeable change in the shading of the recorded
on the channels. Remove the canister by loosen-
picture. However, an increase or decrease of 1
ing. the swivel thumbscrew. Remove the paper
to 2 db is permissible if the change occurs gradu-
bag from the canister and put activated carbon in
ally during the transmission of an entire picture.
the space between the inner and outer tubes.
c. Delay in the line will cause different fre-
Shake the canister well to pack the carbon down
quency components of the facsimile signal to be
and fill to within one-half inch of the top. Replace
displaced. This results in a distorted picture.
the paper bag in the canister, making sure that
Delay correcting networks may be used to equalize
the flange projection lies uniformly along the top
frequency transmission rates. A high signal to
surface. Spread the paper bag so that it stays
noise ratio is desirable to eliminate dark streaks
close to the inside of the inner tube. Replace the
(noise) or spots on the recording.
canister by sliding it into and around the three
nuts used as guides. Tighten the swivel thumb-
d. Transmitting signal levels are explained in
(1) through (4) below.
screw until the canister is held firmly in place.
Do not overtighten the thumbscrew since it will
(1) A +26 dbm output signal (0 dbm=1 mil-
liwatt (mw) in 600-ohms), approximately
tend to distort the assembly. Clamp the flexible
15 volts, is available at LINE JACK J5
hose to the exhaust tube with one of the hose
for transmission of facsimile signals over
clamps provided and secure tightly. Slide the
single field wire circuits made up of Wire
free end of the flexible hose through the slot in the
W-110-B or WD-1/TT. The line must
table and clamp it to the blower unit with the
be long enough to attenuate the signal
other hose clamp.
