Microwave Data Systems MDS 4310 Installation, Operation & Field Maintenance page 77

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 radio's
2. Insert an on-channel signal at –120 dBm (.225µV), 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
2. Restore the modem's Configuration Switch, S1, to its original settings or as
recommended in Table B-1 of Appendix B of this manual.
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 4800 baud modem installed. For
additional information on the 4800 baud modem refer to Appendix B.
TEST PROCEDURE
TRANSMIT FREQUENCY, SQUELCH, DEVIATION,
AND RECEIVE AUDIO OUTPUT—For Units with MDS's Internal 9600 BPS Modem
In the following procedures, references to SW1 & SW2 relate to the switches of the Data
Terminal Emulator (Figure 4-2). See Figure 4-6 for an assembly drawing of the 9600 baud
Modem. See Figure 4-9 for the locations of adjustable controls on the transceiver
motherboard.
Set-up
1. Remove the cover from the transceiver by loosening the four captive cover screws
and lifting it straight up. Make a list of the settings of configuration switch S1 on the
modem—they will be changed temporarily during the alignment procedure.
2. Close the Diagnostics Channel and disconnect the HHT.
3. Connect the Data Terminal Emulator to the
4. Connect the transceiver's
using a short length of RG-8/U or RG-214 coaxial cable. Set up the service monitor
to monitor the transmitter's center (channel) frequency.
5. Set the transmitter deviation to minimum by rotating R168, Deviation, fully counter
clockwise.
6. On the modem, set S1 to 6 & 7 ON (Closed), all others OFF (Open).
4-16 FIELD TESTS & ADJUSTMENTS
command on the HHT.
:
connector to the input of the service monitor
ANTENNA
INTERFACE
connector.
INTERFACE
MDS 05-2415A01, Rev. A
connector.