Motorola XTS 2500

Radio Alignment Procedures
25
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 VOCON
board or the transceiver 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 Figure 10.
4. Left-click the desired frequency field (starting with the highest frequency shown).
5. Left-click the PTT Toggle button on the screen to make the radio transmit. The screen
indicates whether the radio is transmitting.