Broadcast Electronics FX-50, Инструкция по эксплуатации

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The reference filter network consisting of U3A and U3B removes the reference frequency component from the
signal to provide a dc correction voltage to 10 MHz voltage controlled crystal oscillator Y1. The output of Y1
varies in response to the correction voltage and is applied to divide-by-ten counter U4 through programmable
jumper J5.
The output of U4 provides a 1 MHz signal to the AFC/PLL circuit board and to programmable counter U5.
Depending on the position of programmable jumper J11, U5 will divide 1 MHz by 8, 10, or 11. The output of
U5 is applied to phase comparator U2 through one shot U6B which operates as a pulse stretcher. Duty cycle
control R20 adjusts the width of the pulse.
PROTECTION CIRCUITRY. Resistors R34 and R35 operate as a voltage divider network. If phase comparator U2
fails, a clamping voltage of approxi1.7 volts will be applied to U3A through diode D2 to maintain the
output range of the VCXO within accept able limits.
If loss of reference frequency occurs, the output pulse of phase comparator U2 will exhibit a 50% duty cycle.
This will ge2.5 volts to maintain the output frequency of the VCXO at a constant 10 MHz.
11.6.3 MASTER CIRCUIT BOARD.
Figure 11-2 presents a simplified schematic of the master synchronous FM booster circuit board. Refer to Figure
11-2 as required for the following functional description.
The 10 MHz reference frequency from the AFC/PLL circuit board is applied to divide-by ten counter U4 through
programmable jumper J5. The output of U4 provides a 1 MHz signal to programmable counter U5 and the
AFC/PLL circuit board. Depending on the position of programmable jumper J11, U5 will divide the 1 MHz signal
to provide a frequency of 125 kHz, 100 kHz, or 90.909 kHz to U6B. One shot U6B and potentiometer R20
operate as a pulse stretcher to provide an output pulse with a 50% duty cycle. This pulse is applied to input
amplifier U7 through programmable jumper J4. Finally, the output of U7 is applied to amplifier U8 through a
band pass filter and level control R26.