Sailor RE2100, Техническое руководство

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3 SERVICE RE2100
In the level detector, which is built-up around the transistor Q14-1, the base-emitter diode is used to
convert the received AC signal to a DC signal. Thus the input voltage to the level detector is almost a
constant and is equal to the diode cut-in voltage. The open loop gain from the aerial input to the level
detector input must then be sufficiently high to produce the required peak voltage of about 0.65V with an
input signal at the receiver sensitivity level.
In the simplified block diagram, the amplification from the aerial input to the level detector input is divided
into four blocks, which are:
1. Front End Unit
2. 2nd Mixer plus 2nd IF Filter
3. 2nd IF Amplifier
4. AGC Amplifier.
If the receiver does not pass the test of the threshold level given below, it is probably caused by a loss
of gain in one of the four blocks.
The gain of the Front End Unit can be controlled directly by the test procedure given in the section 3.6.2.5.,
while the gain of the 2nd mixer and the 2nd IF filter can only be controlled indirectly by the sensitivity test
of the RX module given in section 3.6.1.1.
The gain of the AGC amplifier can be controlled by measuring the detector output level, which must be
almost constant from one module to another, because of the rectifying diode in the level detector. To
control the detector output level, use the check procedure given in section 3.6.1.6.
If the Front End Unit, the 2nd mixer and 2nd IF filter, and the AGC amplifier all perform as expected, the
2nd IF amplifier must finally be examined. The problem may be solved by adjusting the reference voltage
VREF in the AGC circuit. The adjustment is performed by the trimming resistor R203-1 and is described
in section 3.7.1.4.
1. Connect the generator to the aerial socket at the front end unit (module 2).
2. Connect the voltmeter to testpoint TP2-1 for measuring the AC voltage at the earpiece output.
3. Turn the RE2100 on and turn the RF gain control fully clockwise.
4. Choose generator frequency f
G
, generator output level V
G
, and receiver frequency f
RX
according to
point 9.
5. Measure the signal to noise ratio SND/N at the earpiece output (see section 3.5.2.1., point 6 for
instructions about how to measure SND/N).
If the signal to noise ratio SND/N is different from 20 dB, the generator output level must be adjusted
until this value is obtained.
6. Notice the earpiece output at testpoint TP2-1.
7. To control the threshold level of the AGC, increase the generator output level V
G
by 20 dB and
control that the earpiece output level does not increase by more than 2 dB relative to the level
measured in point 6.
8. To control the flatness of the AGC, increase the generator output level V
G
by 50 dB so the total
increase is 70 dB. Control that the earpiece output level does not increase by more than 3 dB
relative to the level measured in point 6.
9.
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