User's Manual

EX7100 Technical Manual - Module Descriptions
©1999 Exicom Technologies (1996) Ltd 7-20 Issue 3 - May 2001
5. Disconnect the analyser input and output from the PCB and reconnect for normal
operation.
Carrier Null
The carrier null should be stable over the long term. If bit error rates climb, carrier
leakage could be the problem.
1. Put the terminal into “Align Mode” with DSBSC mode selected. Refer to Section 4.5.1
(Not to be confused with “Antenna Align Mode” as described in Section 2.11.2)
2. Connect a spectrum analyser via an attenuator to the transmitter’s output to observe
the sampled spectrum.
3. Using a narrow resolution bandwidth observe the on-channel carrier’s level. This
reading should be at least
40 dB (preferably 55 dB) below the two adjacent tones. If
this is not the case, re-null using the two adjustment pots RV201 and RV202 (see
note below) on the main Tx PCB. The adjustment pot RV203 adjusts the I/Q bias
voltage and under normal circumstances will not need adjustment. If adjustment is
necessary, the voltage can be monitored on test point TP201 and should be 1.7V ±
20mV. Upon adjustment of this voltage, re-check the carrier null.
Note: The RF CPU will have to be moved out of the way (but not disconnected) in
order to access the adjustment pots. Do so by removing the four mounting screws
and easing the module out of the way.
7.4.4 UHF Transmitter Module Replacement Procedure
Note: It is necessary to remove the CPU sub-module prior to replacing the Transmitter
module, however, the CPU sub-module can be replaced without removal of the
Transmitter module.
Replacement of the Type 8044 Sub-Module
1. Remove the bottom cover as described in Section 6.1.
2. Note the connector positions and the way that the cables are run (it is important that
all cables are replaced as they were initially run before the module replacement
procedure)
Remove the following connectors from the CPU sub-module PCB
:
PL102, PL103 and PL104
Remove connector PL101 from the Receiver PCB
:
(This connector is attached to W101 on the CPU sub-module PCB)
3. Remove the four M3 screws and washers that retain the CPU sub-module. Keep the
screws in a safe place.
4. Position the new CPU sub-module and replace the four M3 screws and washers.
Tighten the screws carefully
5. Reconnect connectors PL102, PL103 and PL104 on the CPU sub-module and
connector PL101 on the Receiver PCB; ensure that all cables are run as they were
prior to removal.