Transmit Deviation Balance Alignment - Motorola Astro XTS 4000 Service Manual

Radio Alignment Procedures: Transmit Deviation Balance Alignment
6.7

Transmit Deviation Balance Alignment

This alignment procedure balances the modulation contributions of the low- and high-frequency
portions of a baseband signal. Proper alignment is critical to the operation of signalling schemes that
have very low frequency components (for example, DPL) and could result in distorted waveforms if
improperly adjusted.
This procedure needs to be performed at multiple frequencies to allow for proper alignment across
the entire RF band. The RF band is divided into frequency zones with a calibration point (value) in
each zone.
NOTE: This alignment is required after replacing (or servicing) the main board.
Proper alignment requires a modulation analyzer or meter with a frequency response to less than
10 Hz modulating frequency. The modulation analyzer settings during this test should be set for
average deviation, a 15 kHz low-pass filter, no de-emphasis, and no high-pass filter, if these settings
are supported.
This test can be done with either the R-2670 Communication Analyzer or the 8901_ Series
Modulation Analyzer. The method of choice is the R-2670 analyzer.
1. Initial setup using the R-2670 Communication Analyzer:
– Connect a BNC cable between the "DEMOD OUT" port and the "VERT/SINAD DIST/DMM
COUNTER IN" port on the R-2670.
– Press the SPF key on the R-2670 to display the "SPECIAL FUNCTIONS MENU." Move the
cursor to "High Pass," and select 5 Hz on the soft key menu. Select 20 kHz for the "Low Pass"
setting.
– In the "RF Control" section of the R-2670, enter the frequency displayed on the RSS screen.
Move the cursor to the "B/W" setting and select "WIDE +/- 100 kHz" on the soft key menu.
– Place the R-2670 cursor in the "Display" zone. Select "AC VOLTS" on the soft key menu.
Move the cursor to the "Range" setting and select "AUTO."
2. Initial setup using the 8901_ Series Modulation Analyzer:
– Press the FM MEASUREMENT button. (The "Error 03-input level too low" indication is
normal until an input signal is applied.)
– Simultaneously press the Peak – and Peak + buttons. Both LEDs on the buttons should light.
– Press the 15 kHz LP filter key.
3. Select the TX Deviation Balance alignment screen. The screen indicates the transmit
frequencies to be used. See
4. Click the desired frequency field (starting with the highest frequency shown).
5. Click the PTT Toggle button to make the radio transmit. The screen indicates whether the
radio is transmitting.
Figure 6–11 (VHF)/ Figure 6–12 (UHF) on page 6-10.
6-9