Tait Orca 5000 - Power Supplies; Synthesiser and VCO

B - 14 Circuit descriptions June 2003 IPN: M5000-00-105
whose selection is controlled by a line from the
microprocessor. The speaker output is always
available on the accessory connector to drive
an external speaker.
The unprocessed audio from the output of the
demodulator IC (RX-DET-AF) is also available
at the accessory connector.
DSP
All signalling, such as Selcall, CTCSS, DCS,
G-STAR, DTMF and FFSK, and all confidence
tones are generated by the DSP. However, only
Selcall, CTCSS, FFSK and Two-tone are decod-
ed by the DSP.
The DSP operates in half-duplex mode. That
is, its CODEC input and output is switched
between the Tx and Rx audio paths, according
to whether the radio is transmitting or receiv-
ing.
Synthesiser and VCO
The synthesiser receives channel frequency
information from the microprocessor. It then
sets the VCO to the required frequency and
maintains its stability using a phase-locked
loop. There are one or two VCOs, depending
on the radio type. Some bands have one VCO
that covers the whole tuning range of the radio
plus the IF offset, with its output switched to
Tx or Rx. Other bands have a dedicated Tx and
Rx VCO.
A lock detect output from the synthesiser
(LCK-DET) indicates whether the VCO is
producing the correct frequency (the radio is
in lock). If the frequency is incorrect, the lock
detect status prevents the transmitter from
operating, and informs the control microproc-
essor.
The reference frequency for the synthesiser is
provided by the TCXO (temperature compen-
sated crystal oscillator), which is initially set on
frequency using a DC voltage at calibration
(TCXO Calibration test).
Power supplies
+5V-DIG
The +5V-DIG supply provides a regulated 5 V
to the microprocessor and its associated
circuitry. It is controlled by the on/off switch
and a line from the microprocessor.
It provides 5 V to all circuitry that requires
power when the radio is in economy mode.
+5V-AN
The +5V-AN supply provides the power to all
circuitry that requires 5 V when the radio is not
in economy mode, mainly all analog circuitry
in the receiver, synthesiser and audio modules.
It is controlled by a line from the microproces-
sor and is a regulated supply.
+5V-TX
The +5V TX supply provides power for the
exciter stage of the transmitter when the radio
is in transmit mode. It is controlled by a line
from the microprocessor and is a regulated
supply.
+7V5-BATT
The +7V5-BATT supply is the unregulated
voltage supplied to the radio from the battery.
+7V5-ACC
The +7V5-ACC supply is supplied to the acces-
sory connector from the battery through a
switch and a current limiter.
+7V5-SW
The +7V5-SW switched supply is an unregulat-
ed voltage supplied to the radio from the
battery through a switch.
+14V
The +14V regulated supply provides the 14 V
required by the loop filter in the synthesiser.
A switch mode regulator produces this voltage
from the +7V5-SW and +5V-AN supplies.