240
Receiver Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
10.1
Faulty Receiver Sensitivity
Introduction
This section covers the determination of the extent of the receiver’s loss of
sensitivity. Depending on the nature of the fault, a reduction in receiver
sensitivity of 1dB is often due to a reduction in receiver gain of many
decibels. It is therefore easier to measure gain loss rather than sensitivity loss.
Consequently, if the receiver sensitivity is too low, first check the receiver
gain. The procedure is given in
below.
Task 1 —
Determine Extent
of Sensitivity Loss
Determine the receiver gain as follows. The corresponding loss of sensitivity
can then be deduced. Depending on the extent of the loss, continue with
“Excessive Loss of Sensitivity” on page 242
to rectify the fault.
1.
Input an RF signal (not necessarily modulated) of –90 dBm (or –84
dBm with a trigger-base radio) at the RF connector.
2.
Enter the CCTM command
378
to measure the receiver output level.
3.
Note the value
x
returned for the receiver output level. Depending
on the frequency band in which the radio operates, the value should
be:
Note that a change in the input level of 10dBm should result in a ten-
fold change in
x
.
4.
If necessary, measure the RF voltage at the
QN
test point
(see
). (There is access through a hole in the
IF
TOP
can.)
For comparison, the voltages corresponding to the above values of
x
are:
With an unmodulated RF signal the frequency should be 64.000kHz,
provided that the LO1, FCL and LO2 are locked and on the correct
frequency.
5.
Given the value of
x
, go to the relevant section as follows:
■
x
< 1500, go to
“Excessive Loss of Sensitivity” on page 242
(sensitivity is very low)
■
x
< 500 000, go to
“Moderate or Slight Loss of Sensitivity” on
(sensitivity is low)
receiver output level
x
: normally between 500 000 and 6000 000
x
= 500 000: 12mV
pp
x
= 6000 000: 120mV
pp
Summary of Contents for TM8235
Page 1: ...TM8100 mobiles TM8200 mobiles Service Manual MMA 00005 04 Issue 4 June 2006...
Page 10: ...10 TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 62: ...62 Description TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 148: ...148 Disassembly and Reassembly TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 162: ...162 Servicing Procedures TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 178: ...178 Interface Fault Finding TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 258: ...258 Receiver Fault Finding TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 446: ...446 Spare Parts TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
