X-2 Technical Service Manual Technical Description 4-15
Publication No: 15-02047
Volume
The volume control adjusts the audio level between the post mute output
(IC305/A) and the speaker audio amplifier IC2 mounted on the front panel
PCB.
4.5.5 Tune
104-02907 Sheet 1
When the tune function is enabled, a ground is applied to pin 32 of
microcontroller IC403 [104-02907 Sheet 3] from the Tune switch. The
microcontroller detects the ground and sets the output of IC405 pin 20 low
via the I
2
C bus while applying a low on pin 15 thereby selecting transmit
mode (PTT).
The output from pin 20 of IC405 is connected to pin 2 of NOR gate IC14/A
[104-02907 Sheet 1]. When low, the 456.5 kHz carrier (453.5 kHz for LSB)
connected to pin 3 of IC14/A, appears at the NOR gate output pin 1. This
applies the carrier via the driver transistor V13 to the input of the first Tx
mixer IC9.
The low from pin 20 of IC405 also connects to pin 11 of NOR gate IC14/D.
This sets the output of IC14/D high and biases V12 into saturation. The
output of the second cascaded NAND gate IC7/B pin 4 goes low opening
FET gate V14. This stops the carrier being loaded by the sideband filter
Z301.
4.5.6 Tone Generation
The tones are generated by the microcontroller IC403. Outputs from pins 1
and 2 (TCMP2 and TCMP1) are filtered by resistor/capacitor network R245
to R249 and C412 to C414, and provide the audible signals required for
Emergency Call, alarm and warning tones.
4.5.7 A/D Inputs
104-02907 Sheet 3
The microcontroller monitors supply volts and the VSWR signals applied to
its A/D inputs as follows:
Supply voltage
The A line supply volts is applied via resistor divider R410
[F4]
and R413 to
pin 3 of IC403. The microcontroller provides high alarm tone and disables
the transceiver when the supply volts rises above 16.5 V. A low tone occurs
when the supply drops below 10.5 V without disabling the transceiver.
Transmit forward power
The transmit forward power detector output from D1
[B2]
(FWD-PWR) on the
PA assembly is applied via resistor divider R409
[F3]
and R412 to pin 12 of
IC403.
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