Sailor RE2100, Technical Manual

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5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS RE2100
PAGE 5-4
AF OUTPUT AMPLIFIERS
From the AF switches, the signals are led to three different output amplifiers, which are described below.
AF PRE. AMPLIFIER (LOUDSPEAKER OUTPUT)
The purpose of the Pre. Amplifier is to buffer the AF signal before it is led to the power amplifier placed
on module 4 in T2130. The output level can either be controlled by the volume potentiometer or by a
constant voltage divider. The constant voltage divider is used in the situation where an intercom call to
the RE2100 is detected. This situation is indicated by a ringing tone in the loudspeaker and to avoid this
tone from vanishing it must necessarily be kept independent of the volume potentiometer.
EARPIECE AMPLIFIER
The input signal to the earpiece amplifier is fed through the adjustable resistor R52, where the output level
can be selected. The earpiece output can be means of P1 be selected to follow the squelch or not.
0 DBM AMPLIFIER
In this amplifier the AF signal is amplified in order to give a 0 dBm output (in 600 ohm). The 0 dBm signal
is led to the remote control units and it can by means of P4 be selected to follow the squelch or not.
SQUELCH
The squelch is voice activated, which is realized by detecting whether there is a change in the mean
frequency at the AF-filter output. The squelch circuit, which contains limiting amplifier, frequency to
voltage converter, voltage change detector, and hold circuit, generates a signal by which the microproc-
essor controls the squelch switch U07 at the receiver output.
LIMITING AMPLIFIER
U02/2 and U02/1 are connected as amplifier with about 100 dB voltage gain so that the output from U02/
1 will be square wave with the same frequency as the input signal from the AF filter.
FREQUENCY TO VOLTAGE CONVERTER
The signal from the limiting amplifier is fed to the frequency to voltage converter, built-up around C99-
C100, D26-D27, R142, and U02/4. The output from the converter is a voltage with an amplitude
depending on the input frequency.
VOLTAGE CHANGE DETECTOR
The voltage from the frequency to voltage converter is fed to capacitor C98 which only will pass a variation
in the DC voltage. The resulting signal is amplified and filtered in the circuit built around U02/3. The
inverter U01/3 and D22-D23 provide both positive and negative changes in the voltage to be converted
to a positive change before the signal reaches the hold circuit.
HOLD CIRCUIT
The hold circuit has two functions. Fast opening for the AF signal when a conversation begins and keeping
it open for a period after the conversation stops, e.g. during a short interruption of the conversation.
The signal from the voltage change detector is fed to comparator U01/4, which goes high and buffers the
charging of C95 through D21 and R120 when the input signal is higher than the reference voltage
(determined by R127-
R128). The charging is removed from C95 through R119. As long as the voltage on C95 is higher than
the reference voltage determined by R117-R118 the output from the comparator U01/1 will be high.
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