GE LBI-31482 Maintenance Manual Download Page 5

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The pager is also compatible with Quik-Call II two-tone

paging systems, and operates in both individual call and
group call applications.

Timing waveforms for the decoder circuitry are shown in

Figures 4-1, 4-2 and 5-1, 5-2. It is recommended that these
waveforms be studied in conjunction with the circuit analy-
sis for a better understanding of the decoder operation.

Tone Amplifiers & Reeds

When the proper tone sequence is applied to the Pager,

the discriminator output is applied to buffer/amplifier A51-1.

Tone A

When an HE signal containing Tone A is applied to the

Pager for approximately one second, the output at A51-2 is
applied to limiter-amplifier Q53. The square wave output of
Q53 drives reed FL51 into mechanical resonance. The reed
output is applied to tone amplifier Q54 which provides a
gain of approximately 20 dB. The amplifier output is recti-
fied by D52, and the resulting low (-0.2 VDC) is applied to
A52-1.

Tone B

After Tone A has been received, Tone B is applied to the

receiver for approximately three seconds. The tone is ampli-
fied by Q53 and applied to reed FL52. The reed output is
amplified by Q55 (approximately 20 dB gain) and rectified
by D53. The low output (-0.2 VDC) is applied to A53-1.

Individual Call

The one-second low output from Q54 and D52 applied to

A52-1 causes A52-6 to go low for approximately one second
after a delay of 0.6 second (See Figures 4-1 and 4-2). A52-6
then returns to a high state controlled by delay timer C68
and R69. The high at A52-6 causes A52-8 to go low momen-
tarily, and then go high.

After Tone A is received, Tone B causes a low to be ap-

plied to A53-1. The lows applied to A52-1 and A53-1 acti-
vate an “AND” gate in A52, causing the output at A52-11 to
go low for approximately 2.5 seconds. The low at A52-11 is
applied to A54-6, activating the alert tone oscillator.

The continuous tone output at A54-7 is shunted to ground

for 50 milliseconds at 100 millisecond intervals by Q59 to pro-
vide the interrupted alert tone. The alert tone is then applied to
A51-5.

The same time the tone alert oscillator starts, A55-5 and

A55-7 go low. The low at A55-7 is applied to amplifier A51-9,
turning the amplifier on so that messages can be heard.

GROUP CALL

In group call applications, only Tone B is applied to the re-

ceiver. The tone is applied for approximately 8 seconds. This
applies a low to A53-1, causing A53-6 to go low after a 0.3
second delay caused by C72. After a 5-second delay by delay
timer circuit R72, R73, and C73, A53-11 goes low and turns
off Q56. This allows Q57 to turn on, applying a low to A54-6
and a high to A54-3. This causes a continuous, interrupted 3.5
second alert tone to be heard, followed by the voice message.

ANTI-SHOCK CIRCUIT

When the Pager is subjected to a mechanical shock, both

reeds will vibrate and apply a low to pin 1 of A52 and A53.

This causes a high at pin 2 of decoders A52 and A53 which
disables the decoders to prevent falsing.

RESET/MONITOR CIRCUIT

Pressing momentary reset button S52 at any time applies a

negative pulse to A54-9. This drives A54-12 and squelch con-
trol IC A55-13 low. A55-7 then applies a low to audio amp
A51-9 and turns it on. While the reset button is depressed,
noise or any transmission on the Pager frequency will be
heard. Releasing the reset button causes A54-9, A54-12, A55-
13, A55-7 and A51-9 to all go high shutting off the audio amp
and resetting the Pager.

MODE SELECT

When mode select switch S53 is in the SEL (SELECT) po-

sition, A54-11 is high and the Pager operates in the tone and
voice paging mode. Placing S53 in the MON (MONITOR) po-
sition applies a low to A54-11, causing A54-6 to go low and
A54-12 to go high. This causes the Pager to switch to the
monitor mode so that all transmissions on the Pager frequency
can be monitored.

Figure 4-1 - Individual Call Timing Diagram

Figure 4-2 - Individual Call Timing Diagram

Figure 5-1 - Group Call Timing Diagram

Figure 5-2 - Group Call Timing Diagram

LBI-31482