4-12 FIELD TESTS & ADJUSTMENTS MDS 05-2415A01, Rev. A
TEST PROCEDURE ➌: (Continued)
TRANSMIT FREQUENCY, SQUELCH, DEVIATION,
AND RECEIVE AUDIO OUTPUT—For Radios with MDS’s Internal 1200 BPS Modem
Set-up
1. Remove the cover from the transceiver by loosening the four captive cover screws
and lifting it straight up.
2. Connect the HHT and open the Diagnostics Channel.
3. Connect the transceiver’s ANTENNA connector to the input of the service monitor
using a short length of RG-8/U or RG-214 coaxial cable.
4. Close the Diagnostics Channel and disconnect the HHT.
5. Connect the Data Terminal Emulator to the INTERFACE connector.
Transmit Frequency
1. Key the transmitter by raising RTS (SW1 Closed/SW2 Open). This generates a
continuous Mark tone.
2. Measure the transmit carrier frequency; it should be within 100 Hz of the assigned
frequency. If not, adjust the transmitter frequency using the Frequency Adjustment
on the TCXO.
R
M
If Remote Maintenance is installed, use the IF / DF / INCF / DECF commands
instead of adjusting the TX Frequency Adjustment control on the TCXO.
The IF / DF commands increment/decrement the frequency in single steps
while the INCF / DECF commands make larger jumps by adding a space and a
number to the command. (For example: INCF_8 to increase the frequency by
eight steps out of 100.) When finished, type RMST to store the setting.
Data Deviation
1. Adjust the service monitor to read modulation deviation. With the transmitter still
keyed (SW1 Closed), the deviation should be 2.5 kHz ±100 Hz. If not, adjust R168,
TX DEV. for the proper deviation.
R
M
If Remote Maintenance is installed, set R168 fully clockwise and use the
ID / DD / INCD / DECD commands to adjust for 2.5 kHz deviation. The
ID / DD commands increment/decrement the deviation in single steps while
the INCD / DECD commands make larger jumps by adding a space and a
number to the command. (Example: INCD_4 to increase the deviation by four
steps out of 100.) When finished, type RMST to store the setting.
2. Measure the Mark tone frequency. It should be 1200 Hz ± 10 Hz. If not, adjust R2 on
the modem board.
3. Close SW1 and SW2 to generate a Space tone.
4. Check the transmitter’s deviation. It normally falls within 0.5 kHz of the Mark tone’s
deviation.
5. Measure the Space tone’s frequency. It should be 2200 Hz ± 10 Hz. If not, adjust R3,
Space, on the modem board.
6. Unkey the transmitter by removing the Data Terminal Emulator.
7. Turn off S1-3 on the modem PC board.
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