Motorola GM1200E Service Manual download pdf (Page 48)

GM1200E Tuning Procedure

4-2 Radio Tuning Procedure

The Service windows introduce the concept of the “Softpot”, 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 ‘softpot’ 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 DPS 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 Analyzer to measure the deviation should be set to frequency modulation

with de-emphasis switched off and all high pass ﬁlters switched off.

1.2 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 ﬁrst time.

Note: For certain radio models there are two bias voltage settings. For these radios both ‘ Bias 1

Voltage ’ and ‘ Bias 2 Voltage ‘ need to be adjusted when aligning the PA Bias. For models

that only have one bias voltage setting, the ‘ Bias 2 Voltage ‘ will be shown in grey on the

service menu.

1. From the Service menu, select Transmitter Alignment.

2. Select Bias Voltage Tuning 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. Click the button labelled “0” to set the quiescent current temporarily to 0 mA

4. Measure the DC current of the radio. Note the measured value and add the speciﬁed quiescent

current shown in table 4-1. The result is the tuning target.

5. Adjust the current per the target calculated in step 4.

6. Click the Program button to store the softpot value.

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Motorola GM1200E Service Manual Page 48