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When a stereo signal is present, LED 3 illuminates which indicates that left and right audio
is available. Then the stereo signals go to gain stages and out to the RCA jacks on the back
of the cabinet. These can be used for off-air monitoring of the audio signal. Incoming fre-
quency can be monitored from the frequency monitor BNC jack on the back. The stereo
buffer, stereo decoder, and gain stages and have no effect on the signal that goes through
the transmitter.
The power supply is fairly straight forward. The incoming 12 volt supply goes to a 7809, 9
volt regulator (VR1) which supplies all 9–volt needs on the board. The 9 volts also supplies
a 7805, 5 volt regulator (VR2) which supplies all 5–volt needs on the board. Plus and minus
12 volts from the motherboard is filtered and supplies various needs on the board. Finally
there is a precision reference voltage. Two 2.5 volt reference shunts act very much like a
very accurate zener diode to provide a precision 5 volt supply to the metering board.
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FM600 User's Manual
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