AT&T Bell System Plant Series Alignment Instructions page 3

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F1/F2 MODULATOR
4.09
Tests 1 through 6 (Table A) measure the
level of the output of the modulator at the
terminal test cord.
4.1 O
Tests 7 through 12 measure the frequency
of the output of the modulator.
SIGNAL GENERATOR AND DISTORTION
MEASURING CIRCUIT
4.11
Tests 13 through 18 check the operation of
the distortion measuring circuit and cor-
relate the distortion meter readings with the
thresholds of the hit counter.
4. 12
Test
19
tests the distortion meter on iso-
lated hits.
4.13
Test 20 checks the sync logic circuitry.
4. 14
Test 21 checks the over-all timing sequence
of the signal generator.
4. 15
Test 22 checks the register on the hit
counter.
F1/F2 DEMODULATOR
4. 16
Test 22 is a measurement of data distor-
tion in a looped back path consisting of
signal generator, modem, and distortion measur-
ing circuit. The test is a check of the residual
distortion introduced by the modem.
4. 17
If the demodulator passes the above test,
it is sufficient to plug the rear terminal test
cord into the GS jack and observe the same indi-
cations. This test tests the F2 operation of the
demodulator.
4. 18
In the case of demodulator malfunctions,
it is necessary to make , the tests outlined
in the demodulator section, 5.06 through 5.13.
CHANNEL SELECTOR
4. 19
The channel selector is used in making nar-
row-band and wide-band sectionalizing
tests on a 4-wire facility. Narrow-band sectional-
izing tests are those made on the 4-wire side of
ISS 1, SECTION 107-302-500
the Bl data terminals. Transmission, frequency,
noise and data distortion tests may be made on
each of the Bl data channels. The bridging ampli-
fier and channel selecting circuitry is used in
making the transmission, frequency, and noise
measurements ( 4.20 through 4.22). In addition
to these circuits, the measurement of disortion
of a data channel involves the channel demodu-
lator ( 4.23 through 4.26) and the F11F2 demodu-
lator. On the supervisory channel, in addition to
these tests, demultiplexing tests may be performed
to monitor the E lead signals. The supervisory
data distortion and demultiplexing tests are dis-
cussed in 4.29 through 4.32.
4.20
Wide-band sectionalizing tests are those
made on the 4-wire facility of a full voice
channel. Transmission, frequency, noise, and data
distortion measurements may be made. The 906A
is not used in making the transmission, frequency,
and noise measurements. In making data dis-
tortion tests, the signal is connected directly to
the Fl/F2 demodulator (4.27 and 4.28).
BRIDGING AMPLIFIER AND CHANNEL
SELECTING CIRCUITRY
4.21
This section describes the test for check-
ing the operation of the circuits that per-
mit high impedence monitoring of the signal in
each of the six data channels and the supervisory
channel of the Bl data carrier system as they
,appear on the 4-wire facility. Signal power, noise
power, or the signal frequency may be measured
in any of the channels. The portion of the 906A
involved consists of a bridging amplifier ( CP52),
bandpass filters (included in FL2, 5, 6, and 7),
and channel selector relays (CHl through CH7).
4.22
Each of the seven channels has a bandpass
filter; the channel selector relays select the
output of the proper channel filter. The gain of
the bridging amplifier is adjusted by the channel
selector relays to match the loss of channel filter
so that the average of the power at the mark and
space, frequencies, as measured on the transmis-
sion measuring set, is within 0.4 db of actual
power on the line. However, the channel filter may
introduce an additional difference in power be-
tween the mark and space frequencies of up to
0.8 db.
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