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15. When rotating the frequency scale pointer over the entire scale there
will be a signal (meter deflection) only inside the desired frequency
range.
Note! If there is no blocking of the frequency at all check that the
REMOTE CONTROL plug is well home. If the frequency range is not
correct start procedure over once again from F. 1.
G. Automatic Regulation of the Output Power.
By means of the compressor circuit it is possible to regulate the output
from the oscillator. When a constant output voltage is required, the output
voltage from the Oscillator is used as a control voltage. A constant current
is obtainable if the voltage drop across a resistor connected in series with
the load, is used as the control voltage, and a constant sound pressure is
maintainable with the aid of a regulating microphone. The microphone is
placed in the sound field from a loudspeaker, driven by the Oscillator.
The microphone output voltage is then used as control voltage.
It
is
essential that the frequency characteristic of the microphone and the
microphone amplifier is linear.
Proceed as follows:-
1. Calibrate the Oscillator as described under Frequency Calibration, see
under A.
2. Set the MATCHING IMPEDANCE switch in the desired position.
3. Connect the load to the LOAD terminals or to the screened output
socket on the top of the instrument, see B and C.
4. Feed the control voltage to the COMPRESSOR INPUT terminal. If
necessary use an amplifier which has a linear frequency characteristic
for the amplification of the control signal. Approximately 3 volts is
required for full utilization of the compressor.
5. Set COMPRESSOR VOLTAGE and OUTPUT LEVEL to maximum
(fully
clockwise).
6.
Feed to voltage to be measured to the recording instrument, e.g. the
Level Recorder Type 2305.
7. Set the COMPRESSOR SPEED switch in one of the positions: 30, 100,
300 or 1ooo dB/sec (as required for measuring stability).
8. Regulate the desired output voltage by turning
COMPRESSOR
VOLTAGE knob counterclockwise.
Note: When the Beat Frequency Oscillator is used in conjunction with the
Level Recorder Type 2305 the
writing
speed of the Level Recorder should
be kept below the regulation speed of the compressor.
It is also possible to obtain different regulation characteristics dependent
on the position of the potentiometer marked OUTPUT LEVEL. This can
be seen from Fig. 1.2.
21
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