Channel Demodulator - AT&T Bell System Plant Series Alignment Instructions

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4.23 To check the operation of this portion of
the circuit, perform the following test:
(a) Connect output of 600-ohm balanced oscil-
lator (OSC jack) to LD cord and ground
sleeve of cord. This can be done by using the
BRIDGE GS jacks if available. Operate key
FREQ-NSE to FREQ and block key READ
operated. Set oscillator for 640 ±2· cps read-
ing on frequency counter. This is the mark
frequency for channel 1.
(b) Restore FREQ-NOISE key and operate key
TMR-TMS to TMR. Adjust oscillator for
reading of 906 -24.0 ±0.1 dbm.
( c) Disconnect LD cord and connect oscillator
to MON cord through circuit of Fig. 1.
The OSC IN and MON TEST jacks may be
used if they are available. Set switch CHAN
SEL to 1. (Relay CHl operates.) Record to
nearest 0.1 db the reading on the transmission
measuring set.
MON
CORD
B==°~
246A
JACK
4990
4990
600
TO
n
~
VARIABLE
LI
"1....o FREQ
246A OSC
JACK
RESISTORS ARE l06C
Fig. 1 - Jack Circuit
(d) Repeat (a) through (c) for a frequency
of 840 cps, which is the space frequency
for channel 1. This reading must be within 0.8
. db of that in ( c) ; if not see 5.28.
( e) Average of recorded readings should be
within 0.4 db of the reading in (b).
(f) Repeat (a) through (e) for the following
settings of the CHAN SEL switch and pairs
of frequencies :
155 1, SECTION 107-302-500
Mark Space
Relay
CHAN SEL
Operated
cps
2
1118 1318 CH2
3 1595 1795 CH3
4
2073 2273 CH4
5
2550 2750 CH5
6 3028 3228 CH6
SUPV 315 385 CH7
Note: When finished, return all keys to normal.
4.24
If any of the averages of the mark and
space power are not within 0.4 db of the
input power, see 5.15 through 5.30. The operation
of the relays may be checked using SD-73022-01,
Sheet B7.
CHANNEL DEMODULATOR
4.25
This section describes the test for check-
ing the circuitry that shifts the frequency
band of the data channel, selected as in 4.20 and
4.21 to the F2 band so that the data distortion
may be measured. The portion of the circuit that
performs this function consists of a channel de-
modulator on CP51, low-pass filters included in
FL5, 6, and 7, a channel amplifier on CP51, the
channel selector relays CHl through CH7, and
relays TMC and DDC. The channel demodulator,
which shifts the frequency band, is supplied with
the necessary carrier frequencies from a Bl data
carrier supply unit. The carrier frequency appro-
priate to the selected channel is connected to the
channel demodulator by the channel selector
relays.
4.26
The output of the channel amplifier is con-
nected to the Fl/F2 demodulator ( 4.16
through 4.18) and the data distortion is then
measured as in the over-all tests. Therefore, it
is necessary that the data demodulator and dis-
tortion measuring circuit are working properly
so that sectionalizing data distortion measure-
ments may be made. Thus, it is assumed that these
tests arJ satisfied before performing the test de-
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