Models 691A/692A/693A/694A Section III
Paragraphs 3-1 to 3-20
SECTION 111
OPERATION
3-1. INTRODUCTION. control of the marker sweep. Each control is calibrat-
ed and has the full frequency range of the Oscillator.
3-2. The 690 series Sweep Oscillators are electron-
ically tuned microwave signal sources. Each Oscil-
lator is capable of four types of sweep: start-stop, 3-10. The Sweep Oscillator has provision for auto-
matic leveling of output power. Normally, however,
marker, A F, and external FM. The first three sweeps output power is unleveled and has the power-frequ-
are internally generated, while external FM permits ency characteristic of the RF oscillator. For both
remote tuning. The internally-generated sweeps have leveled and unleveled operation POWER LEVEL is an
adjustable, calibrated end points and sweep times as
well as a choice of sweep modes. The FM sweep has uncalibrated output attenuator.
adjustable rest (CW) frequency.
3-11. Automatic leveling maintains output power con-
3-3. For start-stop sweep independent controls de- stant as frequency changes and is achieved by a
termine the start and stop frequencies. Each frequency closed loop feedback system. A typical leveling sys-
tem consists of a directional coupler for obtaining an
can be set anywhere within the Oscillator frequency RF sample of known proportion, a crystal detector
range allowing output frequency to increase or de- to sense the RF level variations, and an amplifier to
crease with time.
furnish a signal of appropriate polarity and magnitude
3-4. Marker sweep is the same as start-stop sweep to control the RF source and maintain RF output con-
stant. In practice, power is not held absolutely con-
except for a separate set of tuning controls and fre- stant, but variations can be confined within narrow
quency registers. limits.
3-5. AF sweep is a narrowband, variable-width
sweep centered on a CW frequency. The CW frequency 3-12. Standard Sweep Oscillators contain the loop
can be set anywhere within the range of the Oscillator, amplifier mentioned above, other components of the
and sweep width is variable from 0 to 10 per cent of leveling loop being provided externally.
the fill frequency range.
3-13. Provisions for oscilloscope or graphic recorder
display of swept-frequency measurements include a
3-6. For external FM sweep operation any frequency sawtooth voltage output of constant amplitude which
within the Oscillator frequency range can be selected can be used as a time base or frequency axis, pen
as the no-signal (CW) frequency with RF sweep width,
rate and symmetry controlled by the externally-gen- lift on the two slowest sweeps to raise X-Y recorder
erated FM signal. pens between sweeps, RF shut-off (blanking) between
sweeps, manual trigger and manual sweep for display
calibration, and visual indication of sweep duration
3-7. For start-stop sweeping, two internal RF fre- for positive determination of sweep start and stop.
quency markers can be individually positioned any-
where within the selected sweep range. Each marker
is produced by amplitude modulation of the RF output
at the frequency selected. Since each marker is push- 3-14. GENERAL OPERATING INFORMATION.
button-selected, one or both markers can be used. 3-15. OUTPUT POWER RANGE.
The triangular marker pulses are available at a rear- 3-16. Typical maximum unleveled RF power output
panel output and there is amplitude control for the
R F-modulating pulses. of the Sweep Oscillator considerably exceeds the min-
imum specified in Table 1-1. While actual maximums
depend upon the individual BWO tube, typical maxi-
3-8. Common to all three internal sweeps are the mum unleveled RF output is about 800 mw for the
sweep modes, the sweep time selector, and modulation Models 691A and 692A, and 200 mw for the Models
capabilities. Each sweep may be automatically re- 693A and 694A.
current, manual, or triggered. Automatically recur-
rent sweeping can be synchronized with the power line 3-17. RF INPUT LIMITATION.
frequency by rotating the vernier of the sweep time
selector to a detent position. In the manual sweep 3-18. NEVER APPLY MORE THAN 1 WATT RF (CW
mode output frequency variation is operator-con- OR PEAK PULSE) FROM AN EXTERNAL SOURCE
trolled. In the trigger mode sweeping is initiated TO THE SWEEP OSCILLATOR RF OUTPUT.
either by a front-panel pushbutton or by external
negative signals. 3-19. .BWO LIFE.
3-9. For fixed-frequency (CW) operation, either of 3-20. The backward-wave oscillator tube (BWO),
two controls can be used to set the output frequency: used as the RF source in the Sweep Oscillator, is
the start control of the start-stop sweep or the start warranted against electrical failure for a limited
02280-1 3-1
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