4-18 FIELD TESTS & ADJUSTMENTS MDS 05-2415A01, Rev. A
Data Deviation (Continued)
Note—There is some interaction between R168 and the TX Frequency adjustment on
the TCXO. If the shift is equal in both directions, but exceeds 1.6 kHz, it may be
necessary to turn the deviation down slightly and repeat this step. Continue to
alternately adjust R168 and the TX Frequency adjustment on the TCXO until equal
1.6 kHz shifts are obtained.
3. With the high and low shifts equal, set TXD low (SW2 Open). The transmit
frequency should be within ± 200 Hz of the assigned (channel) frequency. If not,
adjust the TX Frequency adjustment on the TCXO as described in the Transmit
Frequency procedure above.
4. Set RTS high (SW1 Closed) and turn ON S1-3 on the modem.
5. Adjust the Transmitter HF Audio Compensation control, R179, if necessary, to
produce 2.7 kHz ± 75 Hz deviation as measured on the service monitor.
6. Unkey the radio by setting RTS low (SW1 OPEN).
7. Turn OFF S1-3 on the modem.
Receive Audio Output Adjustment
1. Generate a –60 dBm (225 µV) signal on the receive frequency with 1 kHz
modulation at 2.5 kHz deviation.
2. Using an oscilloscope set to a 5 ms timebase, observe the waveform at U3 Pin 7 on
the modem board; it should be a 0.7 to 0.75 Vp-p sinewave riding on 2.5 Vdc. If not,
adjust the Receive Audio Level control, R25 (on the transceiver’s motherboard), to
produce 0.7 to 0.75 Vp-p at TP1.
Squelch Adjustment
1. Using an oscilloscope set for DC coupling and 2 V or 5 V per division, observe the
Receiver Unsquelched (RUS) signal at Pin 10 of the
INTERFACE connector.
2. Insert an on-channel signal at –120 dBm (.225 µV), with a 1 kHz tone and 2.5 kHz
deviation. Adjust R41, Squelch Threshold, fully counterclockwise while observing
the oscilloscope display.
3. Set the squelch to be fully closed at this signal level by advancing R41 until the
oscilloscope pattern changes from about 8 V to 0 V. Watch for noise on the scope
display, and advance R41 slightly farther, if necessary, until the signal level remains
at about 0 V.
Putting Things Back Together
1. Restore the transceiver’s time-out timer duration to the original value (if changed)
using the PTOT_XXX command on the HHT.
2. Restore the modem’s Configuration Switch, S1, to its original settings or as
recommended in Table C-1 of Appendix C.
3. Reconnect the RTU’s interface cables to the transceiver and reinstall the cover.
Reconnect the antenna feedline.
4. Confirm that the unit operates normally with the associated RTU. Secure all cables,
providing strain relief if necessary, and check connectors for tightness.
This completes the set-up of the transceiver with a 9600 baud modem installed. For
additional information on the 9600 baud modem refer to Appendix C in this manual.
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