BRUEL & KJAER 1022 Instructions And Applications page 13

When the capacitor is set to frequencies above 20kHz or below 20Hz the
signal from the fixed oscillator is blocked so that no output voltage is
obtained. This has the advantage that when automatic recordings are being
taken with the Level Recorder 2305, no unwanted curves appear on the
paper. The cut-off section can be made wider by means of the adjustable
cams fixed on the capacitor spindle (Fig.4.5). The Remote Control plug is
also needed to make certain connections inside the instrument. By th is
method the overall frequency range of the apparatus can be reduced to
about one octave. In applications where the 1 022 is used with the Level
Recorder 2305 the adjustable cams can be made to operate the pen I ift ..
A 1000 Hz reference signal can be supplied at the output sockets when
the Reference Oscillator is connected and the scale pointer is set to the
position 1000 Hz Ref.signal. The use of this reference signal can be seen in
the operation chapter.
The signals from the fixed and variable oscillators are mixed and then
passed to a low-pass filter. The filter has a cut-off frequency of 50 kHz and
is used primarily to eliminate any 100- 120kHz or 220- 240kHz compo-
nents.
The filtered signal is then fed to the output amplifier. This will give an
output power of 2.5 W nominal load (i.e. the load indicated on the Match-
ing Impedance switch). The output amplifier is current limited to protect
the transistors.
Finally the output signal is fed to an auto transformer for impedance
matching with the load. The markings 6-60-600-6000f2 around the
Matching Impedance Switch indicate the minimum load impedances that
should be used for each switch position. The signal can also be passed to an
output attenuator which allows output signals to be selected between
120 J.J.V and 12 V, (full scale deflection), in accurate 10 dB steps. The over-
all accuracy of the attenuators is 2%. The voltage at the output terminals is
indicated by a transistor voltmeter which measures the average value. It is
calibrated in RMS values of a sinusoidal voltage and the accuracy over the
frequency range 20-20,000 Hz is 1.5% at full scale deflection. Additionally,
there is a dB scale which gives dB values re 1 volt. It should be noted that
when the Attenuator Output is used, the output voltage only equals the
corresponding meter deflection when the impedance of the load connected
to the terminal is high compared with the 50.Q attenuator impedance.
The sensitivity of the voltmeter is automatically changed when the posi-
tion of the Matching Impedance switch is altered. Full scale meter deflec-
tion in volts is indicated for each switch position. The Attenuator switch is
similarly marked and in addition has dB values re 1 volt.
13