Tait TB7100, Service Manual

Page: 272 / 370

274 Transmitter Fault Finding (50W/40W) TB7100 Service Manual
© Tait Electronics Limited October 2005
Frequency Bands
Some fault-diagnosis tasks require programming the radio with the lowest,
centre or highest frequency in the radio’s frequency band. The relevant
frequencies for the different bands are listed in
Table 14.2 . Note that the
following frequency ranges are reserved worldwide for use by distress
beacons:
■
B1 band: 156.8MHz ± 375kHz
■
H5 band: 406.0 to 406.1MHz
Do not program the radio with any frequency in the above ranges.
Can Removal
There are five cans shielding the bulk of the transmitter circuitry:
■
PAD TOP
■
PAF TOP
■
DIRC TOP
■ PIN TOP
■
LPF TOP
To remove any can, first remove the main-board assembly from the chassis.
In the case of the
PAD TOP
and
PAF TOP
cans, first detach the heat-transfer
block from the main board. Secure the block again after removing the cans.
Follow the procedures given in
“Disassembly and Reassembly” on page 99 .
Can Replacement
Replace all cans that have been removed only after repairing the board.
An exception is the B1 band, however, where the
LPF TOP
can must be in
place if the transmitter is to operate correctly.
Table 14.2 Lowest, centre and highest frequencies in MHz
Band Lowest frequency Centre frequency Highest frequency
B1
H5
H7 136
400
450 155
435
485 174
470
520