Tx Centre Frequency Alignment; Figure 7-1 Under (Increase Level); Figure 7-2 Over (Decrease Level); Figure 7-3 Correctly Aligned Waveform - RELM BK RADIO SDMX920 Technical Manual

MX920 Base Station & Repeater
7. Adjust the Reference Deviation digital potentiometer until the top of the
waveform is flat. If the waveform top droops increase the level (see Figure 7-1)
and if it peaks reduce the level (see Figure 7-2).
8. Repeat steps 5 through to 9 until the correct peak deviation and modulation
balance is obtained.
Examples of incorrect, observed waveforms are as follows:

Figure 7-1 Under (increase level)

The waveform when correctly aligned should look as follows:
Choose 'OK' to accept the changes made. This then saves the changes that you have
made to the radio.
After balancing and setting the correct peak deviation is necessary to align the
reference oscillator and re-check the deviation alignment, as the reference oscillator
alignment affects the deviation. This may require running through the deviation
alignment again after the oscillator alignment procedure.

7.1.10 TX Centre Frequency Alignment

The reference oscillator alignment is used to set the correct centre frequency for each
channel. This is done on a per channel basis. Oscillator alignment is done using a
digital potentiometer adjustment through the Built in menu system. To carry out this
procedure the transmitter output needs to be connected to a RF test set displaying the
frequency error. This procedure should be done after the deviation alignment
procedure has been done. Transmitter modulation we be disabled.
Select Tx Reference Oscillator and Output Power and follow the in built menus
instructions. Alter the Reference Oscillator Frequency potentiometer until the channel
is "on frequency". Choose 'enter' to accept the changes made. This then saves the
changes that you have made to the radio.

Figure 7-3 Correctly Aligned Waveform

Figure 7-2 Over (decrease level)

Technical Manual
2003 Revision