Broadcast Electronics AM-2.5E, User Manual, Page: 242 / 320

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1-153. The mono/stereo mode decoder circuit consists of: 1) latches U44B, U51A, and U51B and
2) mono/stereo decoder logic U41D, U43B, U43C, U52C, and U52D. Latches U51A and
U51B latch the two bit binary code and produce complementary outputs for application to
the mono/stereo decoder logic. Latch U44B operates as a clock for U51A/U51B. The
mono/stereo decoder logic decodes the binary code and outputs a HIGH to: 1) transistors
Q5, Q9, and Q14 and 2) equalization select integrated circuits U23 and U28. Transistor
Q14 will respond by generating a LOW internal stereo status signal. Transistor Q5 will
output a LOW to bias stereo indicator DS3 to on. Transistor Q9 will respond by
generating a LOW remote stereo status signal.
1-154. Selection and indication of the mono left, mono right, and mono L+R modes of operation
are performed in an identical manner. When the mono left or mono right mode is
selected, a HIGH will be routed to NAND gate U43D. The output of U43D will go HIGH.
The HIGH is inverted at U55D to produce a LOW mono single channel signal for
application to the exciter circuit board. When the mono left, mono right, or mono L+R
mode is selected a HIGH is applied to transistor Q13. Q13 will respond by generating a
LOW remote mono status signal.
1-155.
EQUALIZATION SELECTION.
Equalization circuit selection is determined by the antenna
connected to the transmitter. Antenna A selects equalization circuit 1. Antenna B selects
equalization circuit 2. Antenna C can be programmed to select equalization circuit 1 or
equalization circuit 2.
1-156. Antenna A, B, and C status signals are applied to AND gates U41A and U41B.
Programmable jumper P6 selects equalization circuit 1 or equalization circuit 2 for
antenna C operations.
1-157. The circuit selects equalization circuit 1 or 2 when a status signal is applied to
U41A/U41B. For example, a LOW is applied to U41B when antenna A is selected. U41B
will output a LOW to NAND gate U43A. Programmable jumper P7 programs the
equalization selection circuit for momentary or continuous signals. With P7 programmed
for momentary signals, U43A will output a HIGH to AND gate U41C. With a HIGH from
U41A, U41C will output a HIGH to latch U44A. U44A will output a HIGH to:
1) integrated circuits U23 and U28 to select equalization circuit 1 and 2) transistor Q4.
Q4 will go LOW to bias equalization 1 indicator DS1 on.
1-158.
PILOT SIGNAL.
A 25 Hz square-wave signal from the exciter circuit board is applied
through potentiometer R132 to a band-pass filter consisting of integrated circuits U30A
and U30B. Potentiometer R132 is designed to provide pilot level control. The band-pass
filter converts the square-wave signal to a sine-wave signal.
1-159. The output of the band-pass filter is applied through switch S1 to: 1) integrated circuit
U23 and 2) inverter U31A. U31A inverts the signal for application to integrated circuit
U28. Switch S1 is provided to disable the pilot signal.
1-160.
POWER SUPPLY FILTER NETWORK.
The stereo circuit board operates from
±
15 volt
power supplies. Each supply is equipped with a filter network. The +15 volt supply filter
consists of inductor L1 and capacitor C92. The output of the filter is applied to the stereo
circuit board components. The -15 volt supply filter consists of inductor L2 and capacitor
C94. The output of the filter is applied to the stereo circuit board components.
1-161.
ECU POWER SUPPLY ASSEMBLY.
1-162. The ECU assembly is equipped with a modular 40W switching power supply assembly.
The supply provides reg5V, +15V, and -15V operating potentials for the ECU
circuit boards.