Tait T860 Series II, Service Manual

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M860-00-Preliminary
T865 General Information B1.3
Copyright TEL 30/06/98
1.1 Introduction
The T865 is a high performance microprocessor controlled FM base station receiver
designed for single or multichannel operation in the 220 to 270MHz frequency range.
The receiver is a dual conversion superhet with a synthesised local oscillator. The first
IF is 21.4MHz, allowing exceptionally high spurious signal rejection to be achieved in
the receiver front end. The second IF section (455kHz) combines amplitude limiting,
detection 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 optional 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 T865 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.