Sailor RE2100, Technical Manual

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5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS RE2100
5.4 EXCITER UNIT (MODULE 4) PART NO. 625634
The exciter module is modulating an audio frequency into a carrier frequency. After some amplification
and filtration the modulated signal is led to the power unit (module 8) for further amplification and filtration.
AF SELECTOR
The exciter unit is able to handle three kinds of AF signals: the microphone signal, the tune/alarm tones,
and some AUX. AF signals. The wanted signal is selected by the analog switch U01, which is switched
on by means of the OP-amp. U03. To select the microphone input, the microprocessor sends an 8-bit
signal to the shift register U07, which controls the analog switch U01/2 by means of U03/4. The other two
AF inputs can be selected in the same way.
From U01 the AF signal is led to the amplifier U02 and through C10 to the compressor circuit. To handle
the AF signal the analog switch U01 and the OP-amp. U02 are biased with R04.
COMPRESSOR AND AF LIMITER
The audio signal from the amplifier U02 is attenuated by means of R20 and the FET Q01. A DC voltage
applied to the gate of Q01 controls the attenuation.
From the amplifier U04/1 the audio signal is split into two ways. One way to the AF limiter and another
way to a dual rectifier. The rectified audio pulses are compared to a DC level determined by means of D02
and R35. A strong audio signal creates new pulses out of the comparator amplifier U04/2 and into C25,
which gives a DC voltage to the gate circuit of Q01.
If the audio signal is so quick and strong that the compressor is unable to handle it, the transistors Q02,
Q03, and Q04 cut the peaks of the signal. The cutting symmetry is adjusted with R57.
CARRIER LIMITER AMPLIFIER
To ensure a constant carrier level to the modulator U05, the transistor Q05 works as an amplitude limiter.
The carrier input signal from the synthesizer unit is amplified in Q06. The transistor Q07 controls the bias
voltage of Q05 and Q06. To switch on the carrier signal to the modulator, the transistor Q07 is switched
on by means of U07 or by an external wire connected to pin 19 in plug P01.
MODULATOR
The carrier signal from the carrier limiter amplifier Q05 is applied to the modulator U06 pin 10. The audio
signal from the AF limiter Q04 is applied to U06 pin 1. The audio signal is multiplied by the carrier signal
in U06, and the resulting modulated signals on pin 12 and pin 6 are added in the transformer TR01. The
output from TR01 is a double sideband signal with suppressed carrier. With R190 the carrier suppression
can be adjusted.
MODULATION LEVEL AMPLIFIER
The modulated signal is led to the voltage divider R77, R78, and R85. The mode selector circuit is forward
biasing one of the diodes D10, D11, or D12 to select the wanted modulation level for the modulation mode
in question. The wanted modulation level is led to the amplifier Q09, and then to the SSB crystal filter where
the unwanted upper sideband is removed. The amplification is adjusted with R87.
CARRIER LEVEL AMPLIFIER
The carrier signal is led to the voltage divider R95 and R96. The wanted amount of carrier insertion for
R3E or H3E mode is selected by one of the diodes D14 or D15 and led to the amplifier Q10. The diodes
D14 and D15 are controlled by the mode selector circuit. In the J3E mode no carrier is wanted, and
therefore D14 and D15 are reverse biased, while D18 is forward biased to short-circuit any carrier signal
for Q10.
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