Sailor RE2100, Technical Manual

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3 SERVICE RE2100
3.6.1.5 CHECK OF AGC CIRCUIT
In this test the attack and decay time of the automatic gain control is controlled by measuring the step
response of the AGC circuit.
In J3E mode (SSB) the attack time is determined by the resistors R89-1, R91-1 and capacitor C72-1, while
the decay time is determined by R63-1 and C69-1.
In H3E mode (AM) the attack time and decay time are determined by R89-1, R91-1 and C71-1.
The measurement of step response is performed by a sudden increment or decrement of the RF input
level. This step in input level is obtained by toggling the RX mute relay, which is located at the front end
unit. The relay is controlled by two different service programmes.
The step response will be displayed on an oscilloscope, which with advantage may be a storagescope.
1. Connect the generator to aerial socket at the front end unit (module 2).
2. Connect the oscilloscope to testpoint TP3-1 for measuring the AGC voltage and select AC
coupling.
3. Connect a probe from testpoint TP4-2 (collector of transistor Q01-2, located at front end unit) to
the external trigger input on the oscilloscope.
4. Select external trig source, DC trig mode, and positive slope trig.
5. Turn the RE2100 on and turn the RF gain control fully clockwise.
6. Choose generator frequency and generator output level V
G
as specified in point 12.
7. In points 8-10 the AGC responses are measured with the oscilloscope and they must be similar
to the responses shown below.
NOTE! It may be necessary to adjust trig level to obtain an image on the oscilloscope.
8. To measure the attack time in J3E mode, select service programme SP-04-6.
9. To measure the decay time in J3E mode, select service programme SP-04-6 and change the
setting of the oscilloscope.
NOTE! To change service programme press <STOP>.
10. To measure the attack and decay time in H3E mode, select service programme SP-04-7 and
change the setting of the oscilloscope. Select positive slope trig.
11. Press <TUNE> to leave service programme mode.
12.
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