M8SL2-00-002-812 T855 General Information B1.5
© Copyright Tait Electronics Limited August 2004. All rights reserved.
1.1 Introduction
The T855 is a high performance microprocessor controlled FM base station receiver
designed for single or multichannel operation in the 400 to 530MHz frequency range
1
.
The receiver is a dual conversion superhet with a synthesised local oscillator. The first IF
is 45.0MHz, allowing exceptionally high spurious signal rejection to be achieved in the
receiver front end. The second IF section (455kHz) combines amplitude limiting, detec-
tion and audio preamplification within a single integrated circuit. It also drives carrier
and noise level detectors for signal strength indication and gating the audio output.
RSSI can be used to drive a carrier mute for audio output gating (link selectable) when
the optional T800-04-0000 RSSI PCB is fitted.
The audio section output can be adjusted to deliver >+10dBm to a 600Ω balanced out-
put, and 1W to a local monitor speaker. A flat or de-emphasised audio response is link
selectable.
The synthesiser frequency is programmed via the serial communications port. Eight
channel select lines are accessible via an additional D-range connector (D-range 2 –
T800-03-0000) at the rear of the set.
All components except those on the VCO board are mounted on a single PCB. This is
secured to a die-cast chassis which is divided into compartments to individually shield
each section of circuitry. Access to both sides of the main PCB is obtained by removing
each of the two chassis covers. There is provision within the chassis to mount small
option PCBs.
The front panel controls include gating sensitivity, line level, monitor volume and a
monitor mute switch.
1. Although capable of operating over the 400 to 530MHz frequency range, the T855 has a
5MHz switching range (see Section 1.2.3 and Section 3.1).
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