M850-00
T855 General Information
B1.5
Copyright TEL 31/09/98
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,
detection and audio preamplification within a single integrated circuit. It also drives
carrier and noise level detectors for signal strength indication and gating the audio out-
put. 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 600 ohm balanced
output, 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.
The T855 has a width of 60mm and occupies a single space in a Tait rack frame, which
has the ability to accommodate up to seven standard modules.
1. Although capable of operating over the 400-530MHz frequency range, the T855 has a
5MHz switching range (see Section 1.2.3 and Section 3.1).
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