Models 691A/692A/693A/694A Section III
Paragraphs 3-21 to 3-41
period of time, usually specified in hours of heater 3-31. EEP FUNCTIO IS.
operation. Accordingly, an internal meter registers
hours of heater operation to amaximumof 4000 hours. 3-32. The Sweep Oscillators have four sweep functions
which are designated Start-Stop, A F, Marker, and
3-21. Since operating practices affect useful tube External FM. Four separate pushbuttons, each labeled
for the function it selects, determine the type of
life, swept- f r equ ency operation.
a. always provide adequate ventilation for the in-
terior of the Oscillator by maintaining at least three
3-33. START-STOP SWEEP.
inches of clearance at the sides and rear of the
cabinet; 3-34. For the start-stop sweep function, the sweep
b. ensure that the air filter is clean; and start and stop frequencies are separately adjustable
to any frequency within the range of the Sweep Oscil-
c. avoid prolonged operation of the Sweep Oscillator lator. Since the output frequency of the Oscillator
with the LINE switch at STANDBY. Although there is varies from the start frequency to the stop frequency,
no RF output in this state, both the BWO heater and sweeping can be either up or down with time. In ad-
the time meter are energized. dition, sweeping can be automatically recurrent,
triggered or manual, with variable sweep time for
3-22. MAGNETIC INTERFERENCE. recurrent and triggered sweeping. All amplitude
modulation capabilities can be used with the start-
3- 23. Sweep Oscillator performance can be adversely stop sweep and output power may be leveled or un-
affected by strong external magnetic fields such as leveled. Instructions for obtaining start-stop sweep
those produced by magnetrons and large transformers. are given in Figure 3-3.
Conversely, a strong permanent magnetic field exists
near the Sweep Oscillator whether or not it is oper- 3-35. AF SWEEP.
ating. Therefore, devices sensitive to magnetism
3-36. With AF sweep, output frequency varies upward
should not be used close to the Sweep Oscillator.
through a band segment adjustable in width from zero
to 10% of full band and centeredon any frequency with-
3-24 CONTROLS, CONNECTORS & in the range of the Oscillator. All trigger and ampli-
INDICATORS.
tude modulation capabilities may be used and sweep
3-25. Front- and rear-panel controls, connectors, time, in the automatic and triggered modes, can be
and indicators are shown dnd described in Figures varied from 10 milliseconds to 100 seconds. RF
3-1 and 3-2. Locations and descriptions apply to output power may be leveled or unleveled. Figure
each of the Models 691A, 692A, 693A, and 694A. 3-4 gives instructions for obtaining A F sweep.
3-37. MARKER SWEEP.
3-26. BASIC OPERATING PROCEDURES.
3-38. Marker sweep is similar to start-stop sweep
3-27. TURN-ON.
with individual start and stop frequency controls and
a. Set rear-panel 115-230 switch to match line frequency registers which are separate from those of
voltage, and check that the fuse has correct rating. the start-stop sweep. The only functional difference
(Correct fuse rating is directly above the visible num- between start-stop and marker sweep is that the RF
ber on the switch slider.) frequency markers cannot be used with the marker
b. Connect Sweep Oscillator to power source. sweep. Figure 3-5 gives instructions for obtaining
marker sweep.
c. Set front-panel LINE switch to RF. After about
one minute delay the RF indicator should glow. Fail- 3-39. EXTFM.
ure of the indicator to glow is an indication of trouble
3-40. The External FM function provides a means of
within the instrument. obtaining output frequency which varies under the
CAUTION control of an externally-produced signal. Output fre-
quency variation which is linear with time results
Do not use the Sweep Oscillator if the cooling from application of a voltage variation which is alqo
fan does not operate at turn-on. linear with time. Positive-going voltage causes out-
put frequency to increase while negative-going voltage
has the opposite effect. Maximum upward deviation
3-28. STANDBY OPERATION. obtainable is the full frequency range of the Oscillator,
3-29. When the LINE switch is set to STANDBY there but downward deviation is restricted to approximately
is no RF output, but heaters of all electron tubes are one-half the Oscillator?s frequency range. Rest (CW)
heated and operating potentials are supplied to all frequency of the FM sweep is calibrated andmanually
circuits except the RF oscillator. This permits nearly adjustable over the full frequency range. When rest
immediate RF output when the LINE switch is set to frequency is set below mid-range, total deviation can
RF, provided at least one minute has elapsed between be full band. The external FM input is direct-coupled
OFF and STANDBY. to permit remote frequency programming.
3-30. With no FUNCTION selectors depressed, the 3-41. During external FM operation both the SWEEP
CW dial lamp will glow regardless of the settings of SELECTOR and SWEEP TIME switch are inoperative,
other controls. but there is full amplitude modulation capability and
02280-1 3 -3
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