Radio Tuning Procedure
Maintenance 3-9
The Service windows introduce the concept of the ÒSoftpotÓ, an analog SOFTware controlled
POTentiometer used for adjusting all transceiver alignment controls. A softpot can be selected by
clicking with the mouse at the value or the slider or by hitting the TAB key until the value or the slider
is highlighted.
Each Service window provides the capability to increase or decrease the ÔsoftpotÕ value with the
mouse, the arrow keys or by entering a value with the keyboard. The window displays the minimum,
maximum, and step value of the softpot. In addition transmitter tuning windows indicate the
transmitter frequency and whether the radio is keyed.
Adjusting the softpot value sends information to the radio to increase (or decrease) a DC voltage in
the corresponding circuit. For example, increasing the value in the Reference Oscillator tune window
instructs the radio microprocessor to increases the voltage across a varactor in the reference
oscillator to increase the frequency. Pressing the Program button stores all the softpot values of the
current window permanently in the radio.
In ALL cases, the softpot value is just a relative number corresponding to a D/A (Digital-to-Analog)
generated voltage in the radio. All standard measurement procedures and test equipment are
similar to previous radios.
Refer to the RSS on-line help for information on the tuning software.
Perform the following procedures in the sequence indicated.
Note: All tuning procedures must be performed at a supply voltage of 13.2V unless otherwise
stated. The Modulation Analyser to measure the deviation should be set to frequency
modulation with de-emphasis switched off and all high pass Þlters switched off.
7.2 PA Bias Voltage
Adjustment of the PA Bias is critical for proper radio operation. Improper adjustment will result in
poor operation and may damage the PA FET device. For this reason, the PA bias must be set before
the transmitter is keyed the Þrst time.
1. From the Service menu, select Tx Alignment.
2. Select Bias Voltage to open the bias voltage tuning window. If the control voltage is out of
range, an error message will be displayed. In this case the radio hardware has a problem and
tuning must be stopped immediately.
3. Press the Toggle Bias button to set the quiescent current temporarily to 0 mA. The status bar
will indicate that the bias is switched off.
4. Measure the DC current of the radio. Note the measured value and add the speciÞed quiescent
current shown in table 3-3. The result is the tuning target.
5. Press the Toggle Bias button to switch on the quiescent current again.
6. Adjust the current per the target calculated in step 4.
7. Press Program to store the softpot value.
Table 3-3 Quiescent Current Alignment.
RF-Band Target
UHF
VHF
440mA±10%
150mA±15%
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