Tait TM8235, Руководство по обслуживанию

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260 Transmitter Fault Finding (40W/50W) TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
Frequency Bands
Where test procedures or figures differ according to the frequency band of
the radio, the frequency band is given in brackets. The frequency band may
be referred to as either ‘VHF’ (very high frequency) or ‘UHF’ (ultra high
frequency) or identified by the frequency sub-band, such as ‘B1’ or ‘H7’.
For example:
A definition of frequency bands is given in “Defining Frequency Bands” on
page 126 .
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 11.2 .
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 129 .
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.
RF output power: > 60W ( VHF ), > 52W ( UHF )
current: < 15A ( VHF ), < 12A ( UHF )
Table 11.2 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