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Technical Description
The transmitter is based around two active plug-in modules, one Control module
(including modulator) and from two to six PA modules. Two passive backplanes
provide interconnection between the modules and the combiner for the PA modules.
The inclusion of a built-in RF tuning and matching system means the transmitter
can easily be adjusted to run on any transmit frequency in the band from 531 to
1602kHz.
To optimise reliability each plug-in module has its own built-in power supply.
The PA modules have a hot-swap capability should the need arise. The PA modules
are based on Class D technology for high efficiency.
Full facilities are provided to control the transmitter either by local manual
control or by external remote control. Options are provided to operate at two
individually pre-set reduced power levels, if required, for example day and
night operation. A full set of alarms is included for both manual and remote
status monitoring and fault diagnosis. Forward and reverse power metering is
provided in addition to a demodulated monitor output
The 150 & 225W transmitters (2 and 3 PA modules per transmitter) are
convection cooled but require a ventilated clear space of 3U above and below the
transmitter case. From 300W an additional cooling fan tray is added below the
transmitter case and controlled as required by a precision thermistor and a unit
mounted on the Control module.
For higher power outputs, or in systems where a higher degree of redundancy is
required, a pair of transmitters can be supplied in a single cabinet with a
passive combiner and forward and reverse power meter.
The HCD S4 transmitter is designed to work with an external transmitter
frequency drive and HCD manufacture a suitable range of crystal drives with
stability ranging from ±10Hz/year to <0.2Hz/year depending on the
application. For full broadcast use a pair of crystal drives is usually supplied
with an auto-changeover in a separate 3U 19" subrack.
Combined Transmitter Pairs:
To either achieve higher output power, up to 900W, or for applications where a
parallel pair is required for redundancy reasons two transmitters can be
supplied as a combined pair in a single cabinet. These systems are set-up to
suit the customers requirement for example with separate mains supplies and
programme feeds. The cabinet is supplied pre-wired and tested ready for easy
installation.
Transmitter Drive:
HCD can manufacture and supply crystal drives suitable for the S4 transmitter. A
range of frequency stability is available from ±10Hz/year to 0.2Hz/year all
causes. Either single drives or pairs of drives with an auto-changeover can be
supplied.
Drives supplied as 21HP
wide, 19" subrack mounted modules. For quasi-synchronous applications
crystal drives locked to a GPS signal are available.
In-Line Power Meter:
HCD manufacture in line power meters to allow continuous monitoring of forward
and reverse transmitter output power primarily for remote monitoring and control
of the complete transmitter system.
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