Moderate Or Slight Loss Of Sensitivity; Front-End Calibration And Tuning Voltages - Tait TM9100 Service Manual

10.3

Moderate or Slight Loss of Sensitivity

This section covers the case where the receiver has suffered a moderate or
Introduction
slight loss of sensitivity. As measured in Task 1, the receiver gain will be less
than 500 000, but not as low as 1500. With a gain less than 40 000, the loss
of sensitivity will be moderate — about 15mdB too low; otherwise it will
be slight — just a few decibels too low. There are three tasks:
The fault-diagnosis procedures of
the differences are minor they are important.
If the loss of sensitivity is moderate or slight, the fault is probably in the
Task 7 —
Front-end
front-end tuning circuitry.
Calibration
and Tuning Voltages
1.
2.
3.
4.
5.
6.
7.
8.
234 Receiver Fault Finding
Task

7: front-end calibration and tuning voltages

Task 8: moderately low receiver sensitivity
Task 9: slightly low receiver sensitivity
Using the calibration application, check the calibration of the front-
end tuning circuitry: Open the "Raw Data" page and click the
"Receiver" tab.
Record the values listed in the "Rx FE Tune BPF Settings" field — these
are the DAC values of the FE (front-end) tuning voltages for the five
frequencies FE TUNE0 to FE TUNE4.
(FE TUNE0 is the lowest frequency and FE TUNE4 the highest fre-
quency in the radio's frequency band; the values are given in
Table 10.2.)
For each of the frequencies FE TUNE0 to FE TUNE4 in turn, carry out
the following procedure: Enter the CCTM command 101 a a 0,
where a is the frequency in hertz.
Enter the CCTM command 376 and record the value returned — this
is the front-end tuning voltage in millivolts.
Compare the values measured in
DAC and voltage values listed in
If the DAC and voltage values are correct, go to
not, go to Step 6.
Recalibrate the receiver using the calibration application, and check
the DAC and voltage values again.
If the DAC and voltage values are now correct, the fault has been
rectified; go to "Final Tasks" on page
Step 8.
if the receiver output level x measured in
Go to Task 8
than 40 000; otherwise go to
Task 8 and Task 9 are similar; although
Step 2 and Step 3 with the nominal
Table 10.2.
Step
147. If they are not, go to
Task 9.
TM9100 Service Manual
© Tait Electronics Limited August 2005
8. If they are
Task 1 was less