TM8100/TM8200 Service Manual Transmitter Fault Finding (>25W) 269
© Tait Electronics Limited November 2007
Emergency
Frequencies
The following frequency ranges are reserved worldwide for use as maritime
emergency frequencies or 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 board 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 135.
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.
Transmit Tests The following actions need to be taken when carrying out transmit tests:
■ secure the board
■ ensure the proper antenna load
■ limit the duration of transmit tests
■ protect against accidental transmissions
■ avoid thermal and RF burns.
These points are discussed in more detail in the following sections.
Secure the Board Before conducting any transmit tests, ensure that the board is adequately
secured in the chassis. This is essential if overheating of the radio is to be
avoided. (As mentioned earlier, the heat-transfer block must already be
secured to the main board of the assembly.) It is good practice to secure the
assembly by at least the two external screws and one of the internal screws.
The screws are labelled
I and E in Figure 5.3 on page 139. There is no
need, however, to secure the lid of the radio body.
Table 11.2 Lowest, centre and highest frequencies in MHz
Band
Lowest
frequency
Centre
frequency
Highest
frequency
B1
G2
H5
H7
K5
136
350
400
450
762
155
375
435
485
816
174
400
470
520
870
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