5. Electrical Interface
The AH-4 uses 12 volt inverted logic and an “open collector” transistor to ground to perform signaling.
The radio provides 13.8 volts to the tuner. It also provides a START line that is pulled up to 13.8 volts
inside the radio. The radio pulls the START line to ground to assert the signal (start the tuning
operation). Similarly, the AH-4 pulls the KEY line to 5 volts through a 22 K ohm resistor/diode
combination. The radio also pulls this line to 13.8 volts through a resistor. The AH-4 pulls this line to
ground to assert the signal (indicate tuning status to the radio.)
6. Revision History
Revision Date
Description
2
2019-05-22
Formatting for PDF presentration
1
Original
AH-4 Operation
K9EQ
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