User's Manual

SRM9000X8 800MHz SERVICE MANUAL
© TMC Radio 2008 page 52 TNM-M-E-0022 Issue 1
Calibration procedure
1
Select
Tx Power/Mod
page.
2
Select
Channel 0
.
3
Select the
1W
power level.
4 Set the microphone input signal from the Audio Generator to 1000Hz at 400 mV RMS.
5
Select
PTT
and adjust the
VCO Modulation Limit
DAC to give a maximum peak deviation of 2.30kHz.
6
Reduce the microphone input level to 40mV RMS and check that the deviation is within the range ±1.25
kHz to ±1.75 kHz.
7 Repeat steps 5 to 6 inclusive for the remaining three Channels (1, 2, & 3).
8 Remove the microphone audio input signal
9
Select the
Generate Square Wave
function.
10 While viewing the de-modulated signal on the transceiver test set oscilloscope, set to DC coupling,
adjust the
Modulation Balance
slider for the best square wave symmetry.
Refer to Note below
11 Repeat steps 9 to 10 inclusive for the remaining three Channels (2, 1 & 0).
12
Release the
PTT
button.
Note: The FM demodulator on the measuring equipment also requires DC coupling for this test to provide
correct results. If an HP8920A is used, the top and bottom of the square wave must be set with a 16.6%
negative slope.
ie. For a waveform of 4 divisions p-p (neglecting overshoot) the slope should be adjusted to 0.3 divisions.