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Description.
Gt>neral.
The Beat Frequency Oscillator Type 1013 is designed for measurements in
the frequency range 200-200ooo Hz and consists of an oscillator, mixer,
and an amplifier section.
It
works on the heterodyne principle using two
high-frequency oscillators, one of which operates on a fixed frequency, while
the frequency of the other can be varied by means of a variable capacitor.
The required signal frequency is obtained as the difference between the two
high frequencies and can be read off a large illuminated scale, the pointer
of which is connected to the variable capacitor. The scale is logarithmic and
graduated from 200 to 200ooo Hz, and in addition an INCREMENTAL SCALE
is provided, allowing exact frequency selection in the range - 500 to
+
500
Hz for any setting on the main scale.
The frequency adjustment is carried out by obtaining a beat between the
fourth harmonic of the line voltage and the oscillator voltage, occurring when
the oscillator is tuned to this frequency and the push-button marked LINE
FREQUENCY BEAT FOURTH HARMONIC on the front panel is pressed.
The variable capacitor has two control knobs, one of which is directly
connected to the capacitor spindle and is used for quick setting of the
approximate frequency. The other will, when pressed, rotate the spindle
with a ratio of 1 to 5 and allow fine tuning to the desired frequency.
A worm gear permits the capacitor to be tuned automatically, for example
by the aid of the motor in the Level Recorder Type 2305. The mechanical
connection to the Level Recorder is effected by means of a flexible shaft
which can be screwed onto the bushing on the side of the Oscillator cabinet.
The worm gear can be engaged and released with the aid of a built-in
electromagnetic clutch, operated from a switch on the front panel marked
AUTOMATIC SCANNING or by a remote control
arrangement.
The electro-
magnetic clutch is a friction device, so that manual tuning of the variable
capacitor is possible even when the clutch is engaged.
The Beat Frequency Oscillator is provided with frequency modulation. A
reactance tube, controlled by saw-tooth oscillations from a built-in oscillator,
may be switched into the circuit of the fixed oscillator. The frequency of
the saw-tooth oscillator is controlled by the switch marked MODULATION
FREQUENCY, and the amplitude of the saw-tooth oscillations, which controls
the frequency deviation, is regulated by FREQUENCY DEVIATION.
Provision is also made for external modulation whereby very wide limits of
frequency modulation can be obtained.
3
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