Table of Contents
Advertisement
Oscillator, or it can also be operated from an external switch or relay. In the
latter case connection must be made to the appropriate terminals of the jack
marked REMOTE CONTROL on the front panel, and the control switch
AUT. SCANNING for the magnetic clutch must be in position "Off".
By means of a pushbutton marked 10ooo Hz REF. SIGNAL, an extra
capacitor is introduced in the tuning circuit of the variable oscillator.
There viii be exactly lOooo Hz at the output socket when the scale pointer
is set to 10ooo Hz REF. SIGNAL and the pushbutton 10ooo REF. SIGNAL
is depressed.
The reason for setting the scale pointer at 10ooo Hz REF. SIGNAL is in
order to be able to align the 1013 with the frequency calibrated paper, used
on the Level Recorder Type 2305, as this paper is calibrated from 10 Hz. The
distance between the calibration mark of 10 Hz and 20 Hz on the recording
paper corresponds to the distance between 1oooHz REF. SIGNAL and 200Hz
on the oscillator.
By depressing the pushbutton it is now possible to check that the level of
the middle frequencies is within the divisions of the paper.
The voltage developed across the grid circuit of the variable oscillator is fed
to the mixer tube via a buffer amplifier stage. This stage, which prevents
undesired coupling between the fixed and variable oscillator, also increases
the signal level to a value required for correct functioning of the mixer.
The mixer tube is a triode
giving
a low hum level in
spite
of the AC heating
of the filament.
A low-pass filter with a cut-off frequency of 500 kHz is inserted in the anode
circuit of the mixer tube, passing only the lower frequency obtained by the
frequency conversion to the grid circuit of the first tube in the output
amplifier section.
Partial Blocking of Frequency Range.
As previously mentioned, the frequency scale is logarithmic and calibrated
20Q-20ooo Hz. When the capacitor is set to frequencies above 20ooo Hz
or below 200 Hz the fixed Oscillator can be blocked, and consequently no
output voltage will be obtained. For automatic recording of frequency
characteristics, i.e. when using the Level Recorder Type 2305, this is a great
advantage as no unwanted curves will then appear on the corresponding
section of the frequency calibrated paper.
The cut-off section can be made wider by adjusting the cam discs, connected
to the rear end of the capacitor spindle.
It
is possible to cut down the fre-
quency range to approximately one octave in any part of the range of
200-200ooo Hz. However, if the REMOTE CONTROL plug is removed there
will be no blocking at any part of the scale.
In application where the B.F.O. is employed in conjunction with the B
&
K
Level Recorder, and where automatic recording is required, the blocking
arrangement can also be used for remote lifting of the Level Recorder's
writing pen. This is a great asset in for example measurements where the
7
Advertisement
Table of Contents
