Codan Radio Radio Repeater Systems Training Guide - Manual (Page 27)

RADIO REPEATER SYSTEM | TRAINING GUIDE
Chapter 3: Repeater System Equipment Page 19
c) System Regulator modules
The system regulator is a module that incorporates voltage regulators, an audio output stage, and a
means of metering various stages of the receivers and transmitters mounted in the same subrack.
One special feature of the voltage regulation stage is an anti-latchup hysteresis circuit. This is a switch
that turns off at a selected voltage and turns on at a different voltage. This feature is particularly useful
when the repeater is powered by solar cells. In a standard installation, if the solar array does not recharge
the battery fast enough (not enough sunlight), the repeater will discharge the battery completely and
the repeater will stop operating. When the solar cells get some illumination they will start to charge the
batteries and the repeater will come back to life for a short time, at least until the battery’s output voltage
falls below the repeater’s operating point. With the hysteresis switch, the repeater is disconnected from
the batteries when their voltage falls below approximately 8 volts, and it remains disconnected until
the solar array has had a chance to charge the battery up to some higher voltage, usually around 11
volts. This differential arrangement prevents the repeater from turning on and off the air by allowing the
power supply to receive a signifi cant charge before having to power the equipment. These hysteresis
voltages can be changed if different voltage levels are required for turn-on and turn-off. (eg. 10 volts
turn-off, 11.5 volts turn-on).
d) Control Cards
Each system may have an audio control card that routes audio, muting and COR-PTT signals, or
a serial data control card that routes LVDS serial data and analog / digital COR-PTT signals. Each
control card is set up for the specifi c confi guration of the repeater / base station. Setting up the control
card with the specifi c confi gurations allows the transmitter and receiver modules to be swapped out and
replaced with other receiver / transmitter modules for maintenance and troubleshooting procedures,
without affecting the operation of the system.
e) Equipment Isolation
An important feature to consider is equipment isolation. By this we mean the amount of coupling between
the transmitter and receiver other than through the antenna and associated duplexers / multicouplers.
The amount of coupling between receiver and transmitter is highly variable and often causes problems
which only show up after the installation is complete. The low-power repeaters are compact, and it is
possible to arrange 2 receivers, 2 transmitters, a system regulator and the required control cards side
by side in a 19 inch rack. This close physical spacing between the various components can create
problems and so close attention must be paid to unit shielding. Each of the components (receiver,
transmitter, system regulator, etc.) is mounted in an extruded aluminum enclosure which provides
a continuous Radio Frequency Interference (RFI) tight seal. All leads entering these enclosures are
fi ltered to prevent RFI from either entering or leaving on an unintended path. Double shielded co-axial
cable between receivers, transmitters and duplexers is often used to enhance the isolation. With careful
selection of a duplexer it is possible to operate a transmitter / receiver pair at a frequency spacing of
less than 400 kHz, although this is not recommended.