a. Setting Controls. The following procedure
Unit O-5B/FR. The output of the exciter unit
sets the controls of the facsimile transceiver, the
is a frequency-shift rf signal which shifts above
the converter, and the exciter unit to produce the
and below a center frequency by an amount
required carrier shift:
proportional to the varying dc signal produced
by rectification of the 1,800-cps signal. This
(1) With maximum signal of +2 db from the
serves as the rf excitation for the cw transmitter.
The transmitter output is a frequency-shift signal,
unit and the FREQ. ADJ. (R2) control
shifting a total of 800 cycles between picture white
of the converter so that the transmitter
and picture black; 400 cycles above and 400 cycles
output frequency is 400 cps above the
below the assigned carrier frequency (a total of
assigned carrier frequency. Check by
1,200 cps, 600 cycles under the old shift limits)
using Audio oscillator TS-382A/U and
tuning for zero beat.
vantageous because they are affected less by
(2) With minimum signal from the facsimile
fading and interference than transmissions using
transceiver, adjust the facsimile trans-
conventional am and, in addition, the rf channel
ceiver until the transmitter output is 400
width required is less than when using am SCFM.
cps below the assigned carrier frequency.
b. Receiving. When receiving frequency-shift
This will require adjustment of the
facsimile signals, a conventional communication
CONTRAST and GAIN controls of the
facsimile transceiver. While adjusting
receiver that has a crystal-controlled temperature
transceiver controls, check again to be
compensated hf oscillator and a stabilized beat-
sure that the maximum transceiver signal
frequency oscillator should be used. Radio Re-
ceiver R-390/URR or Radio Receivers BC-779,
is maintained at +2 db. Do not make
any further frequency control adjust-
BC-794, and BC-1004 modified in accordance
ments on the exciter unit or the con-
with MWO SIG 11-866-4, Modification of Radio
verter. Use Audio Oscillator TS-382A/U
Receivers BC-779-(*), BC-794-(*) and BC-1004-
to see that the change from minimum
(*) to provide for improved stability of the high
facsimile signal to maximum facsimile
frequency oscillator circuit, are suitable in this
application. However, a conventional receiver
signal increases the transmitter output
may be used to pick up the frequency-shift radio
frequency by 800 cps. To do this, leave
signal with a stable rf signal applied to its input
the oscillator tuned as described in (1)
from Frequency Meter BC-221. Therefore, the
above, and measure the frequency of the
beat-frequency oscillator will not be required. In
beat note produced by the beating of the
both methods, the incoming signal is heterodyned
oscillator signal with the transmitter
with the local oscillator signal to produce an output
output signal. Use the beat note method
in the af range swinging from 1,500 to 2,300 cps
to measure the frequency of this 800-cycle
note either on a direct reading af meter
or from 1,800 to 3,000 cps, depending on which
shift limit is used (fig. 29). These fm voice-
or by comparison with an 800-cycle signal
from an audio oscillator.
frequency signals are applied to the input of
Converter CV-2C/TX which converts them into
(3) To check the accuracy of the adjustments
am af signals which are fed into the input of the
and to assist the receiving operator in
receiving facsimile transceiver.
adjusting the station, send a series of
maximum and minimum level signals
64. Operation
(high- and low-frequency signals), fol-
lowed by a series of phasing pulses. Re-
After the equipments have been connected as
peat this sequence two or three times
shown in figure 28, apply the following operating
before actually transmitting the copy.
instructions when using an 800-cps shift (1,500 to
2,300 cps). Detailed instructions for connecting
Note. Allow at least -hour warm-up period
before making operating adjustments.
and adjusting Exciter Unit O-5B/FR are given in
TM 11-2205A. Audio Oscillator TS-382A/U and
b. Transmitting. Negative transmission of fac-
Electronic Multimeter TS-505/U may be used to
simile copy is preferable, although copy may be
transmitted either negative or positive. The
assist in properly setting up the equipment for
operation.
