TM 11-6625-1668-12
length of 8 (six information bits plus a start and stop pulse) all of equal widths. Under these conditions the
CODE LEVEL switch will override the CHARACTER LENGTH switch. If, on the other hand, the CODE LEVEL
switch remains at 6 but the CHARACTER LENGTH switch is moved to 9, the character will consist of six
information bits and a start pulse all equal to each other in width with the exception of stop pulse which will then
be two bits wide. To summarize the functions of the CODE LEVEL and CHARACTER LENGTH switches, a
character is always two more pulses than indicated on the CODE LEVEL switch. Increasing the position of the
CHARACTER LENGTH switch increases the length of the stop pulse.
(3) Free Run Selected Character Operation. The following is typical of a free run selected character
transmission operating procedure. For purposes of this procedure 22% spacing bias distortion is introduced to
the output signal and a 150-volt, 60-ma neutral loop supply is keyed (fig. 3-7). Assume 150-baud operation.
Control
Position
Control
Position
P-N switch ...............................................
P (Polar)
MESSAGE SELECT switch .......................
M
DISTORTION SELECT switch .................
BIAS S
CODE LEVEL switch.................................
5
PERCENT DISTORTION switches ...........
2
CHARACTER LENGTH switch ..................
8
SELECTED CHARACTER BITS
1 to M
CHARACTER RELEASE switch ................
FREE RUN
switches............................................
OSC switch...............................................
INT
2 to M
BAND RATE switch...................................
150
3 to S
4 to S
5 to S
NOTE
The position of unmentioned controls will not affect operation in this mode.
(a) Connect the power supply return to pin 15, +60 volts to pin 16 and -60 volts to pin 17 of
connector 1A3P3.
(b) Connect adapter 1A3P3 to connector 1A3J3.
(c) Connect a patch cord from the DRY CONTACTS output jack to the equipment under test.
(d) Set the generator POWER switch to ON.
(e) Set the power supply POWER switch to ON and adjust the loop current for 20 ma.
(f) Set the MESSAGE SELECT switch to the SELECTED CHARACTER BITS position.
(h) The SIGNAL indicator lamp illuminates each time the output signal is marking, as the selected
character is generated (requires at least 50-volt polar signal to light the neon lamp).
(4) 1:1 reversals. A continuous pattern of 1:1 reversals may be obtained at the output of the generator
by setting the MESSAGE SELECT switch to the 1:1 position. The 1:1 signal can be distorted by marking,
spacing or switching bias. The percent distortion introduced to the signal is obtained by the combined settings
of the PERCENT DISTORTION switches.
(5) MSG: (internal). With the MESSAGE SELECT switch set to MSG, the generator will transmit either
an 80-character or 128-character test message as determined by the position of the strap in the character
counter, assembly 1A2A8. The strap positions are clearly marked on the assembly when shipped from the
factory. The standard test message provided with the generator is in 5-level Baudot code, an 8-level message
is available as an option. Distortion is introduced to the message by setting the BIAS-END switch to the
appropriate position, marking bias (BIAS-M) spacing end (END-S). The maximum amount of distortion that can
be introduced by generator is 49 %. This distortion is controlled by the combined settings of the PERCENT
DISTORTION switches. One switch controls the distortion in 10% increments from 0 to 40% and the other
switch provides distortion in 1% increments from 0 to 9%.
(6) M (steady mark) S (steady space). A steady mark or a steady space output signal is selected by
means of the MESSAGE SELECT switch. With this switch in the S position a steady space signal is provided
at the output. With the MESSAGE SELECT switch in the M position a steady mark signal is produced. All
other switches are inoperative for steady mark or steady space transmission.
(7) EXT (external message operation). With the generator MESSAGE SELECT switch set to EXT, and
the analyzer DISPLAY MODE switch set to ERROR TEST, the pseudo-random test pattern from the analyzer is
applied to the generator through the rear panel connector and back to the analyzer for system self-test. The
system self-test is performed as part of the maintenance procedures (para 4-10).
3-11
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