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Figure 5-8.
Code Synthesizer Block Diagram
5-63.
Tl1e three modulation sources are sumed together on the Audio Synthesizer module after the level
controls. The composite modulation signal is then switched to the appropriate modulator and applied to the
modulation determination circuitry (MOD CAL AUDIO), the audio amplifier (SPKR AUDIO), and the
Modulation Output jack (MOD OUT) on the front panel. The signal to the front panel jack is buffered by a Driver
Amplifier to provide a low driving source impedance.
5-64.
The AM modulation signal at the output of the Select Switch is sumed with
a
+5 volt signal. This
combination provides a DC level to control the average output power of the wideband amp in the RF Input
module, and
a
superimposed modulation signal to give an AM output. The RF Level control on the front panel
for local control or the Programmable Attenuator on the IEEE module provide local or remote RF level control
by simultaneously attenuating the DC level and the modulating signal. The resulting signal is the AM MOD
&
DC REFERENCE signal to the RF Input module.
5-18
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Figure 5-6.
Monitor Mode Block Diagram
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5-44.
The 10.7 MHz difference signal at the IF port of the receive mixer is amplified and selected by the first IF
Amplifier and Filter. The Amplifier provides sufficient gain so that the overall gain of the RF Input module is 10
±2 dB. The IF filter provides a modulation acceptance bandwidth of ±100kHz. The filter output is the 10.7 MHz
IF signal to the Receiver module (A4).
5-45.
A second mixer in the receiver module down converts the 10.7 MHz IF signal to 455kHz by mixing the
input signal with a 10.245 MHz Second Local Oscillator. The Second Local Oscillator is phase locked to the 10
MHz system standard so that its frequency is as accurate as the standard. The phase locked loop for the
Second Local Oscillator is split between two modules. A 10.245 MHz SAMPLE signal is compared with the
REFERENCE FREQUENCIES from the RF Synthesizer on the Processor 1/0 module (A7). The comparison
provides a TRACKING VOLTAGE error signal to the 10.245 MHz oscillator which corrects its frequency to hold
it in lock.
5-46.
Immediately following the second mixer is the IF filter. The IF filter is selectable between a narrowband
(±6kHz mod acceptance) and a wideband (±'100kHz mod acceptance) bandwidth. The bandwidth is under the
control of the processor and is selected by the bandwidth switch on the front panel.
5-15
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