Model 686C Section I
Paragraphs 1-1 to 1-3
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SECTION I
GENERAL INFORMATION
1-1. GENERAL DESCRIPTION. When used for its primary purpose as a sweep oscil-
lator, the internal circuitry provides an extremely
The @ Model 686C SweepOscillator is one of several wide choice of sweeping rates and band width swept.
@ Electronic Sweep Oscillators which together cover
major microwave bands as shown in Table 1-1. The rate of change of frequency is linear with time
and adjustable in calibrated steps from 32 mc/sec to
320 kmc/sec. The frequency range swept can be as
Table 1- 1. Electronic Sweep Oscillators small as 4.4 mc or the full range of 4.4 kmc, as
selected by a calibrated seven position A FREQUENCY
I @ Model I Frequency Range I switch. In addition, there is a VERNIER control
associated with the A FREQUENCY switch which gives
682C 1.0 to 2.0 kmc
683C 2.0 to 4.0 kmc continuous adjustment between the fixed positions.
684C 4.0 to 8.1 kmc
The minimum sweep time of the Model 686C is approxi-
H01 686C 7.0 to 11.0 kmc mately 14 milliseconds. The sweep time is determined
686C 8.2 to 12.4 kmc
687C 12.4 to 18.0 kmc* by the combined setting of the RF SWEEP RATE and
the A FREQUENCY switches. These switches are
I I I interlocked by a differential gear drive which auto-
Sweep oscillators are used as signal sources for a matically prevents any combination which would pro-
wide variety of laboratory and production tests. They duce a sweep time less than 14 milliseconds.
provide a high level constant amplitude signal that can The swept rf output from the oscillator is linear with
be rapidly changed in frequency. Thus they permit
microwave characteristics of systems or components time, and a 20-25 volts sawtooth voltage is provided
concurrent with each rf sweep to supply a linear time
to be quickly checkedover an entire bandof frequencies. base for an oscilloscope or X-Y recorder. The oscil-
The @ Model 686C Sweep Oscillator is a refined in- lator sweep can be made recurring, or set for single
strument of this general type. It covers the complete sweeps. Single sweeps can be started either by the
front-panel push button or by an externalpositive pulse
X band from 8.2 to 12.4 kmc and uses a Backward- (rise time greater than 3 volts per microsecond).
Wave Oscillator (bwo) tube to generate the rf signal.
The bwo tube has several advantages over thepre-
1-2. INSTRUMENT COOLING SYSTEM.
viously used klystron-type microwave oscillator tubes
when used in sweep-type oscillators: The instrument is forced-air cooled by a high velocity
fan system. The incoming air is filtered to remove
The bwo tube output frequency and power level are excessive dust. This filter must be inspected fre-
determined by the value of the applied voltages only. quently to insure that it is not clogged with dirt. A
There are no cavity or repeller voltages to adjust or dirty filter may restrict air flow sufficiently to cause
track. There is no tendencyto switch modes of oscil- excessive heating of the instrument which can cause
lation. Since frequency and power level adjustments early component failure (see paragraph 4-3).
are electronic, all mechanical problems associated
with tunable cavity klystron-type oscillators are elimi-
nated. Control of frequency and power level is simple, 1-3. THREE CONDUCTOR POWER CABLE
positive and straightforward. By use of an rf leveler
circuit, which programs the rf power output from the To protect operating personnel, the National Electrical
bwo, output power variations of kl. 25 db or less are Manufacturer's Association (NEMA) recommends that
the instrument panel and cabinet be grounded. All
realized. With the rf leveler inoperative, output power @ instruments are equipped with a three-conductor
from the bwo is constant to within rtl. 5 db, but full
power from the bwo tube is obtained. The rf output power cable which, when plugged into an appropriate
receptacle, grounds the instrument. The offset pin
power is continuously adjustable from 0 to maximum, on the power cable three-prong connector is the
which is not less than 10 milliwatts into a matched
waveguide load. ground pin.
The Model 686C Sweep Oscillator is versatile. The To preserve the protection feature when operating this
output can be cw, externally amplitude-modulated at instrument from a two-contact outlet, use a three-
any percentage from 0 to loo%, externally pulse- prong to two-prong adapter and connect the green
modulated, or externally square-wave modulated. An pigtail on the adapter to ground.
internal square-wave source provides square-wave
modulation at any frequency between 400 and 1200 CPS. The magnet power supply is isolated from the chassis,
The oscillator can be frequency-modulated or swept and the polarity of the primary power wiring has been
in frequency over any portion or all of the X band carefully controlled to insure that internal exposed
range of 8.2 to 12.4 kmc. parts and wiring are generally at ground potential.
00034- 1 1- 1 |
ACEC
HEWLETT-PACKARD
