4. AH-4 Radio Interface Operation
The AH-4 interfaces to the radio with a two-wire connection. A START signal is issued by the radio to
start the tuning operation. A KEY signal from the tuner indicates when: the tuning has started; the
tuning has failed; or the tuning has been completed. The tuning operations works as follows:
1. A tuning operation is requested by the radio – the radio asserts the START line.
2. The AH-4 microprocessor is reset and begins running its program after approximately 300 ms.
When the AH-4 is ready, it asserts the KEY line (AH-4 routes the RF through the power divider,
measurement circuitry and tuning network).
3. The KEY signal causes the radio to transmit a carrier at about 10 watts of output power.
4. The AH-4 verifies that the power is between 5 and 15 watts. If not, the AH-4 aborts the tuning
operation.
5. If the power is between 5 and 15 watts, the AH-4 begins the tuning operation.
6. Approximately 250 ms after the AH-4 starts tuning, the radio removes the START signal.
7. When tuning has been achieved, the AH-4 removes the KEY signal and switches the RF to pass
only through the tuning network. The microprocessor is then halted. The radio stops transmitting
when the KEY signal is removed.
8. If the AH-4 was unable to achieve tuning, it removes the KEY signal for 20 ms, asserts it again,
waits 200 ms, then finally removes the KEY signal. This causes the radio to indicate a “not tuned”
condition.
9. If the band is changed on the radio, the tuner is reset. This causes the tuning network to be
removed from the circuit.
The figures below show the various commands and responses to the tuner.
FIGURE 4: SUCCESSFUL TUNING RESPONSE
AH-4 Operation
K9EQ
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