RELEASED: 10/2/2006
Page 27
COMMUNICATI0NS
HSD SERIES OPERATION AND MAINTENANCE
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200 KHz. The output of the phase detector at pin 3 of U6 feeds the loop filter
composed of C24, R7, and C23. R6 and C22 provide additional loop filtering. The
circuits above compose the phase lock loop for the oscillator.
The other output of the VCO flows through the R13 leg of the resistive
attenuator/splitter into amplifier U3 which has a gain of ~11dB and is biased with 3.2
volts at 45ma. The U3 output feeds pin 1 of U4 which divides the input frequency by
four. This provides a phase noise reduction of approximately 12dB. The output of
U4 on pin 4 is now ¼ the input frequency or 418 MHz in NTSC mode or 411.15 MHz
in PAL mode. The U4 output then feeds through amplifier U5 which exhibits a gain
of 13dB and is again biased with 3.2 volts at 45ma. The U5 output flows through a
low pass filter composed of L5, L6,C45, C46, and C47 to the LO port of mixer MX1
with a power level of ~+8dBm.
The balance of the circuitry of the module is centered around microprocessor U7
which programs the phase lock IC (U6). The circuit between pins 7 and 8 of U7 is
the oscillator that provides the clock to U7. The frequency of crystal X1 is 8.898
MHz. Pin 9 is an input read line that sets the frequency to NTSC or PAL mode. The
circuit connected to pin 17 provides turn-on reset control. This circuit holds the reset
low for a short period of time after the power supply comes up to allow a sufficient
time to reach its peak voltage ensuring U7 starts in a known state. U7 always starts
up in reset (low) when power is first applied. Pin 34 of U7 is an input line which
receives an output from the phase lock IC U6. When the PLL is in lock, U6 pin is
high which feeds back to U7 and sets a bit which terminates the programming of the
registers of U6. The input to pin 34 is also split and feeds through R26 to the lock
status driver Q1. The Q1 output connects to the Control Board through J3.
3.4 Output Converter Module:
P/N 50523000
Schematic Diagram 50523002A, D1A3
Digital Mode:
IF Input (J1)
≈
-15dBm average
RF OUTPUT (J4)
≈
0dBm average
Gain (J1-J4)
15dB
Analog Mode:
Visual IF Input (J1)
≈
-10dBm peak
Aural IF Input (J1)
≈
-23dBm average
VISUAL RF OUTPUT (J4)
≈
+6dBm
AURAL RF OUTPUT (J4)
≈
-7dBm
