85-HZ DIVERSITY OPERATION

TM 11-5805-387-34-2

1-70. 85-HZ DIVERSITY OPERATION

When MODE SELECTOR switch S4 is set at 85 HZ DIVERSITY, + 22 volts, +20 volts, and ground are applied to

the appropriate circuits as follows:

The +22 volts from the preregulator is not switched to any special circuitry in the 85-Hz diversity mode.

The +20 volts from the regulator is applied through contacts 6 and 4 of MODE SELECTOR switch S4F to pin 15 of

transmitter module connector XA3, A3J1, energizing divide-by-10 circuit A3A1Q11-Q18 for nsk operation.

Ground is applied through S4A, S4C, and S4F as follows:

Switch S4A grounds receiver module pin XA4, A4J1-6 through contacts 4 and 6, connecting tty squelch adjust

A4A2R1 to ground through A4A2R31 in all nsk modes. This action compensates for the difference in noise

content between fsk signals and nsk signals caused by the wider fsk bandwidth.

Switch S4C grounds the output of 600-ohm voice amplifier A3A2Q8 through contacts 12 and 10, and the

modem 50-ohm mike output through contacts 4 and 6. This action prevents the modem from introducing noise

into the voice input of the associated radio transmitter.

Switch S4G grounds transmitter module pins XA3, A3J1-5 and 8 through contacts 4, 6 and 10, 12, respectively.

When pin 5 is grounded, the output of mixer amplifier A3A2Q2 is applied to the 425-Hz nsk section of FL1

through diode switch A3A2CR3. When pin XA3, A3J1-8 Is grounded, A3A2C1 parallels A3A2C2, narrowing the

pass band of sine wave pass filter A3A2C1, C2, L1 for nsk tones.

1-71. 85-HZ + VOICE OPERATION

When MODE SELECTOR switch S4 is set at 85 HZ + VOICE, + 22 volts, +20 volts, and ground are applied to the

appropriate circuits as follows:

The +22 volts from the preregulator is applied through contacts 12 and 11 of MODE SELECTOR switch S4F to pin

17 of receiver module connector XA4, A4J1. The +22 volts forward biases channel 1 switch A4A2Q3, effectively

grounding the input to receiver module tty channel 1.

The +20 volts from the regulator are applied through contacts 6 and 5 of MODE SELECTOR switch S4F to pin 15

of transmitter module connector XA3, A3J1, energizing divide-by-10 circuit A3A1Q11-Q18 for nsk operation.

Ground is applied through S4A, S4B, and S4G as follows:

Switch S4A grounds receiver module pin XA4, A4J1-6, through contacts 5 and 6, connecting tty squelch adjust

A4A2R1 to ground through A4A2R31. This action compensates for the difference in noise content between fsk

signals and nsk signals caused by the wider fsk bandwidth.

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