User's Manual

EX7100 Technical Manual - Module Descriptions
©1999 Exicom Technologies (1996) Ltd 7-38 Issue 3 - May 2001
Receiver Maintenance Adjustments
The baseband DC offset may drift with age. To check or adjust:
1. Connect an oscilloscope in XY mode to PL301 (pins 1 and 3). Ensure that the
oscilloscope is DC coupled and centred on the display.
2. Disable the transmitter by setting the terminal to On-demand operation in the
Terminal Set-up menu (Refer to Section 3 for details).
3. Put the EX7100 terminal into Align Mode with CW and Tx: Low selected. (Refer to
Section 4.5.1).
4. Apply an un-modulated RF carrier at approximately –80dBm on channel into the
receiver (SK101)
5. A circle should appear on the oscilloscope. Adjust the signal generator RF level for a
circle of ~2 volts peak to peak diameter.
6. Adjust RV301 and RV302 to centre circle about 0 volts (i.e. remove the DC offset).
The quadrature null should seldom require adjustment. To check or adjust:
1. Perform the tests above, but once complete observe the frequency of PL301 (pin 1).
2. Adjust the frequency of the signal generator so that the frequency observed on PL301
(pin 3) is between 5kHz and 10kHz.
3. Place the oscilloscope into single channel mode, AC coupled and observe the signal
at TP304.
4. Adjust RV303 such that the signal at TP304 is at minimum amplitude.
5. Increase the oscilloscope gain (or increase the level of the signal generator) to allow
the signal to remain visible and continue to adjust RV303 for a symmetrical minimum
amplitude sinusoid that should be twice the frequency of the un-nulled sinusoid
measured in step 2. above (i.e. between 10kHz and 20kHz).
7.7.4 VHF Receiver Replacement Procedure
This procedure covers the replacement of both the Receiver and Receiver Front-End
modules.
1. Isolate the EX7100 Terminal from the incoming DC supply by removing the DC input
wires from the rear panel terminal block.
2. Remove the bottom cover as described in Section 6.1.
3. 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).
4. Remove connections PL101, PL103 and PL104 from the Receiver board, also
remove coaxial connectors SK101 & SK102 from the Receiver Front-End module.
5. Remove the four screws holding the Receiver Front-End module and lift the Front-
End PCB out of the casting. Keep the screws in a safe place.