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SMX920 Base Station & Repeater
2060-ohm resistor between pins 4 and 6 of this connector of the SMX920 Base
Station. Temperature calibration is done via the Calibration Screen. To complete the
temperature calibration, follow the instructions that in built menu system provides.
7.1.8 TX Power Adjustment
The transmitter power setup is used to set the correct power for each channel. This can
be done on a per channel basis or all channels can be set at once.
7.1.9 Peak Deviation and Modulation Balance Alignment
This procedure is used to set the peak deviation and modulation balance for each
channel. This can be done on a per channel basis or all channels can be set at once.
The alignment is done using the Alignment Screen in the built menu system . To carry
out this procedure the demodulated output of the transmitter output needs to be
connected to a CRO or some other piece of equipment giving a visual display of the
demodulated output. IF Bandwidth of the RF test set should be set at 20kHz or greater
(230kHz on the HP 8920) and de-emphasise should be off. The audio filters should be
set at <20Hz HPF and 15kHz LPF.
To alter all channels at once use the 'Factory default alignment (All Channels). The
peak deviation is aligned on wide band and without CTCSS\DCS Tone enabled. The
following table specifies the peak deviation to align to.
Bandwidth
Wide (25kHz spacing)
The alignment channel for this routine is the middle frequency band. The test tones
used in this routine are generated internally and are a 1 kHz square wave for the
transmitter deviation and a 400 Hz square wave for the modulation balance.
Procedure:
1.
Using in built menu system, select --- ALIGNMENT MENU –
2.
Now select either to 'Align current channel (Individual)' OR 'Factory default
alignment (All Channels)'
3.
If 'Align current channel (Individual)' select Tx Deviation and Modulation
Balance - current channel
4.
The radio will now transmitter.
5.
Follow the built in menu system instructions.
6.
The transmitter will be modulated with test frequencies (1kHz, & 400Hz tone
generators under micro controller control)
7.
Adjust the VCO Deviation digital potentiometer using built menu system until
the correct deviation is obtained. (See Table 7-1 Peak Deviation Settings).
8.
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).
9.
Repeat steps 5 through to 9 until the correct peak deviation and modulation
balance is obtained.
28
CTCSS Option
NO
Table 7-1 Peak Deviation Settings
Technical Manual
Peak Deviation (Hz)
4800
RELM/ BK RADIO
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