4-4 Radio Programming and Tuning Procedures
4.4 Transmitter Tuning
The following sub-sections contain the procedures to tune the radio transmitter. These procedures
include:
l Power Amplifier (PA) Bias Tuning
l Battery Threshold Tuning
l Reference Oscillator Warp
l DAC Tuning (LowBand radios only)
l Transmit Power Tuning
l Power Amplifier (PA) Voltage Limit Tuning (VHF 1-25W and UHF 1-25W LDMOS radios only)
l Modulation Balance Attenuation
l VCO Attenuation
l DTMF Deviation
l MDC1200 Deviation
4.4.1 Power Amplifier (PA) Bias Tuning
Perform the PA Bias tuning procedure as follows:
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.
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.
CAUTION: To prevent damage to the PA, ensure that the antenna output is always
terminated into a 50 Ohm load
!
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