Transmitter Tuning; Power Amplifier (Pa) Bias Tuning - Motorola CDM Series Basic Service Manual

4-4
4.4

Transmitter Tuning

The following sub-sections contain the procedures to tune the radio transmitter. These procedures
include:

Power Amplifier (PA) Bias Tuning

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Battery Threshold Tuning
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Reference Oscillator Warp
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DAC Tuning (LowBand radios only)
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Transmit Power Tuning
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Power Amplifier (PA) Voltage Limit Tuning (VHF 1-25W and UHF 1-25W LDMOS radios only)
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Modulation Balance Attenuation
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VCO Attenuation
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DTMF Deviation
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MDC1200 Deviation
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4.4.1 Power Amplifier (PA) Bias Tuning
Note: 1. If using the regulated power supply RLN4510 to measure the current drawn by
the radio, remember that the current meter terminals only measure the voltage
drop across a 0.1ohm shunt resistor. Calculate the actual current being drawn
by the radio by dividing the voltage drop across the resistor by 0.1. (V= I*R).
2. Tuning must be performed only for High Power. The tuning screen will show up to
three Toggle Bias buttons numbered 1, 2 and 3. Tuning must be started with the
lowest bias number and continued until all bias points have been tuned.
Perform the PA Bias tuning procedure as follows:
!
CAUTION: To prevent damage to the PA, ensure that the antenna output is always
terminated into a 50 Ohm load
C a u t i o n
1. Under the Tx Align menu, select PA Bias, and then High Power.
2. Measure/read the DC current drawn from the radio (varies from radio to radio). This value should
typically range from 100-700mA. Record this value as X.
3. Press Toggle Bias button for the first bias to enable the PA bias softpot.
4. Increase softpot value to obtain Y until Y - X is within the range given for PA current in Table 4-3.
5. Press Toggle Bias for the first bias again to disable the PA bias softpot.
6. Repeat Steps 5-7 for the remaining Toggle Bias buttons.
7. Program the bias softpot values into the radio by pressing the Program button.
8. Exit the PA bias high power function.
Radio Programming and Tuning Procedures