User's Manual

85894_M&R_TA7650C_A 2-5
on-resistance MOSFET and acts as a switch when the input voltage goes below the wanted
output voltage. IC6 supplies approx. 35V, (input voltage + 8.2V) to the main regulator circuit.
The relay RL1 is the main powerswitch and also acts as a reverse polarity protection because
of D4.
Current measurement is done with IC2. There is also a current limiter (IC5B), which reduces
supply voltage if current consumption is too high.
IC8 generates -5VDC for the TX main board.
2.4.2 Regulator board
This board accepts 21.6 - 31.2VDC input voltage.
The DC voltage is converted to +3.3VDC, +5VDC and +12VDC by switchmode regulators
IC1, IC2 and IC5. All regulator outputs are filtered to prevent noise from interfering on the
Modulator board and TX Main board.
The microcontroller IC4 controls the powerup of the regulators, and controls ON switching of
the equipment via the power relay on the PA board.. It also stores the current powerstate in
the internal EEprom, so that it remembers if the unit was switched on after a power failure.
2.5 Modulator module
The Modulator module consists of the RF frontend board and a shielding box
The Modulator module is plugged directly into the Main board.
2.5.1 Modulator board
The Modulator board can be divided into four main sections:
• I/Q modulator
• I/Q demodulator
• Synthesiser
I/Q modulator
IC4 is a I/Q modulator and the output signal is controlled by the I/Q input signals from the
Main board. The signals are filtered are filtered by LC filters on the inputs. The output signal
is filtered by a tracking filter to improve wideband noise.
IC5 is a powerdetector and measures the output level of the modulator. It is used to tune the
trackingfilter and is also a part of the BITE.
I/Q demodulator
IC2 is the demodulator and demodulates the signal from the directional coupler on the PA
board. It plays a vital part of the control loop of the transmitter. The demodulated signal is