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TYPE 1263-B AMPLITUDE-REGULATING POWER SUPPLY
4.2 SWEEP APPLICATIONS.
If the oscilfator
is
mechanically swept for automatic frequency re-
sponse displays, the dynamic regulation of the output should be checked.
A cathode-ray oscilloscope used to present the response is an excellent
means of checking the operation of the power supply and of observing
when optimum output-coupling setting is obtained. When the Type 1750-A
Sweep Drive is used, connect the blanking cable to the BLANKING tele-
phone-tip jacks on the Type 1263-B Amplitude-Regulating Power Supply
to provide a zero-reference base line for the desired response display
and for the checking display.
The horizontal input to the oscilloscope
should be supplied with the oscilloscope sweep voltage provided by the
sweep
drive.
Temporarily insert a Type 874-T in the cable to the out-
put rectifier and connect the vertical input of the oscilloscope to the
connector thus made available.
The oscilloscope should be set for de
response. Such changes in connection can be made without turning the
power supply off, provided that the selector switch is set to ZERO. Re-
turn the selector switch to OPERATE. Drive the oscillator over the de-
sired level. Adjust oscilloscope sensitivity to give a suitable horizontal
and vertical deflection. For cw operation, the pattern should be approx-
imately rectangular, with the horizontal portions straight lines. The neg-
ative voltage horizontal portion represents the oscillator output char-
acteristic, and the positive portion the zero level.
With 1-kc internal modulation a similar pattern
is
obtained except
that the horizontal portions are traced out by two bright spots connected
by a vertical line. The flatness of the path traced by the lower spot is
the indication of flatness of the oscillator output.
Since the average
value of the modulated output
is
regulated, variation in starting delay in
the oscillator over
its
frequency range will cause variations in the duty
ratio of the square wave and consequently show a variation from flatness.
The use of a matched termination or resistance pad following the output
rectifier will minimize variation of oscillator starting delay.
If the oscillator output characteristic is not shown as a horizontal
straight line, adjust the oscillator output coupling, and, if necessary, re·
duce sweep speed. A broadening or burst of high-frequency voltage on
this line indicates control-system oscillation; to eliminate this, reduce
the output coupling.
For best regulation, some readjustment of the os-
cillator output coupling is necessary with changes in the setting of the
OUTPUT VOLT AGE control, particularly with internal 1-kc modulation.
Sharp discontinuities
in
the output characteristic of the oscillator,
particularly when wide frequency ranges are swept, may require a reduction
in sweep speed so that the control-system response time will permit com-
plete correction of output voltage. With General Radio Unit Oscillators
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