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T885 General Information
B1.3
M880-00
1.1
Introduction
The T885 is a high performance microprocessor controlled FM base station receiver
1
designed for single or multichannel operation in the 800 to 960MHz frequency range
.
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, audio preamplification and RSSI within a single integrated circuit. This IC
also drives a noise level detector for gating the audio output. RSSI can also be used to
drive a carrier mute for audio output gating (link selectable).
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 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 T885 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 800-960MHz frequency range, the T885 has a
6MHz switching range (see
Section 1.2.3
and
Section
3.1).
Copyright TEL
10/07/00
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