Operating instructions

Maintenance DMH Series VHF Radio
Page 5-8 BK RADIO
A. Synthesizer Calibration
This calibration records the required VCO pretuning voltage across the RF frequency
band. This adjustment may be necessary if VCO components are replaced.
No additional setup is required for this procedure.
During the automatic calibration, the synthesizer will attempt to acquire several receive
and transmit frequencies. For each test frequency, the pretune D/A converter voltage will
be varied to determine the optimum value. The LCKDTECT signal is monitored to
determine if synthesizer lock occurs. The D/A voltages that result in proper operation will
be recorded in the radio’s EEPROM memory.
B. Reference Oscillator Frequency
This procedure allows the reference TCXO frequency to be corrected. Transmit and
receive frequencies are derived from the reference oscillator. The reference oscillator
may require adjustment due to crystal aging or if the reference oscillator module is
replaced.
To set up for this procedure, connect a suitable attenuator and frequency counter to the
antenna output of the radio. The attenuator must be capable of handling the full power
output of the radio and protecting the input of the frequency counter. A 30 dB attenuator
capable of 50 Watts is recommended.
Transmit frequency must be measured and entered into the alignment software. Once
these frequencies are obtained, proper settings for Frequency Adjustment are
automatically computed and recorded in the radio’s EEPROM memory.
C. Transmit Power Curve
NOTE: The transmitter should not be keyed for extended periods while setting transmitter
power. Prolonged transmitting will cause the thermal protection circuitry of the
radio to decrease the transmitter power.
This setting is used to help maintain a constant transmitter output power of 50 Watts
across the RF frequency band. If components on the PA board are replaced, this
adjustment may be necessary.
To set up for this procedure, connect a suitable 50Ω power meter to the antenna output of
the radio.
Output power must be observed while interactively adjusting the power at several
frequencies. The final settings are recorded in the radio’s EEPROM memory.
D. Transmit Power Adjustment
NOTE: The transmitter should not be keyed for extended periods while setting transmitter
power. Prolonged transmitting will cause the thermal protection circuitry of the
radio to decrease the transmitter power.
This setting allows customization of transmit high and low power output levels. If
components in the transmitter power circuit are replaced, this procedure may be
necessary.