Tait T800 SL2 25W, Service Manual

Page: 135 / 383

M8SL2-00-002-812
T854 General Information C1.5
© Copyright Tait Electronics Limited August 2004. All rights reserved.
1.1 Introduction
The T854 is a synthesised, microprocessor controlled FM base station transmitter
designed for single or multichannel operation in the 400 to 520MHz frequency range
1
with a standard power output of 25W. The RF section of the transmitter comprises a fre-
quency synthesiser which provides 100mW of frequency modulated RF drive to a two
stage, wide band driver stage followed by a 25W power amplifier. A thermal shutdown
feature is provided in the T854 in case operating temperatures exceed acceptable levels.
The T854 is rated for a continuous output power of 25W at +60
°
C. This is achieved via a
high capacity heatsink, electric fan and shroud. The fan forces air across the heatsink to
dissipate the heat. The heatsink replaces one of the usual T800 covers.
A wide selection of audio characteristics may be obtained from the audio processor.
Optional circuit blocks are an audio compressor and a pre-emphasis stage. They can be
bypassed or linked to one or both audio inputs, and then back into the remaining audio
circuitry in almost any combination. All audio processor options are link selectable.
The synthesiser frequency is programmed via the serial communications port. Eight
channel select lines are accessible via an optional D-range connector (D-range 2 –
T800-03-0000) at the rear of the set.
All components except those of the VCO are mounted on a single PCB. This is secured
to a die-cast chassis which is divided into compartments to individually shield each sec-
tion of circuitry. Access to the PCB is primarily through the top cover of the radio, as all
components are mounted on the top side of the PCB. There is provision within the chas-
sis to mount small option PCBs.
The front panel controls include line sensitivity, microphone socket and carrier switch.
This switch turns on the carrier (unmodulated) as an aid to servicing.
1. Although capable of operating over the 400 to 520MHz frequency range, the T854 has
an 8MHz switching range (see Section 1.2.3 and Section 3.1).