Advertisement
Page 2
Introduction
The Hewlett-Packard 8690B Sweep Oscillator forms the
basis of many types of swept-frequency systems. The 8690B
Sweep Oscillator accepts nine RF units capable of cover-
ing the frequency range from 0.4 MHz to 40 GHz. An
8690B/RF Unit may be used alone or with a wide variety
of accessory equipment. For example, multi-band sequen-
tially swept coverage is provided by employing the HP
8706A Control Unit and up to three 8707 A RF Unit Hold-
ers, permitting the 8690B Mainframe to drive as many as
eight RF unit sweep oscillators.
86908 Sweep Oscillator
The Hewlett-Packard 8690B Sweep Oscillator combines
interchangeable RF units with high accuracy, versatility, and
ease of operation to bring you all the advantages of single
unit sweep oscillators plus economical multi-band capability.
With no adjustments required, the changing of RF units
is quick and easy and the snap-in dial is keyed for accurate
positioning. The front panel has a logical, straightforward
layout for ease of operation. The frequency dial is the full
width of the instrument for maximum resolution.
Careful design of all-new solid-state power supplies re-
sults in exceptionally low residual FM, and provides rugged
protection against system transients.
INC. FM
=
750kHz
j_
250
kHz
T
Fi9ure
1.
Low incidental FM of square-wave modulated
8693B is shown in this oscillogram. Measurement made
with HP 2590B Microwave Frequency Converter.
RF Units
The HP 8698B ( 400 kHz - 110 MHz) and 8699B ( 1
oo
MHz - 4 GHz) Solid-State RF Units provide four decades
of frequency coverage with only two plug-ins. By use of
heterodyne techniques, careful filtering, and advanced mi-
crocircuit technology, broadband coverage is achieved along
with superior performance.
Microwave RF units employ high reliability Backward
Wave Oscillator tubes (BWO) which carry an uncondi-
tional one-year warranty.
Two types of microwave RF units are available, permit-
ting selection to meet any application requirement. HP
PIN diode modulation and leveling are available in the
Model8690B
"B" type RF units from 1 to 12.4 GHz. The 8691-4B RF
Units offer exceptional frequency accuracy (between 0.5%
and 1%) over a wide range of modulation conditions. HP
PIN diode RF units are the only RF units that specify full
power frequency accuracy over a 10-dB dynamic range,
considerably enhancing measurement accuracy. All modula-
tion functions including leveling are performed independent
of the backward-wave oscillator tube (BWO). The result
is the virtual elimination of frequency pulling during either
modulation or leveling, which, in turn, results in extremely
high frequency accuracy and linearity and very low inci-
dental FM. Figure 1 illustrates the low incidental FM
associated with square-wave AM.
The "A" series of RF units employs conventional BWO
grid modulation for AM functions. This series covers the
entire 1-40 GHz spectrum in seven models (8691A-8697A)
and is used in the bands above 12.4 GHz, where PIN attenu-
ators are not available, and in lower bands when modulation
requirements are less demanding.
Sweep Functions and Markers
The 8690B Sweep Oscillators provide a broadband "start-
stop" sweep whose end points can be set anywhere in the
band. Independent controls set the start and stop frequencies
on the slide-rule scale. Thus the units can sweep up or down,
depending only on the setting of the start frequency with
respect to the stop frequency. There is no interaction be-
tween the start and stop control settings. Selecting the start-
stop sweep is simply a matter of pushing a button.
Two independent frequency markers, set separately on
the dial and direct-reading in GHz, can be positioned any-
where in the band. The markers amplitude-modulate the
RF output, providing triangular markers. These markers
have points sharp enough to give high resolution on narrow
sweeps, yet are broad enough to be quite visible on even the
broadest sweeps. Figure 2A shows that the markers are
plainly visible on a full-band sweep. In addition, marker
amplitude can be adjusted from the front panel. Adding
the markers to the display is again a matter of pushing
buttons.
The markers can also be used as end points for a second
broadband sweep which starts at the Marker 1 frequency
and ends at the Marker 2 frequency. Thus, the 8690B
Sweep Oscillators have two independently adjustable broad-
band sweeps, providing a high degree of flexibility. For
example, should the start-stop sweep reveal a particular area
of interest, the markers can be adjusted to bracket the area;
then a simple depression of the Marker Sweep button ex-
pands the bracketed area to cover the full horizontal scale
of the indicating device-oscilloscope or X-Y recorder.
Figure 2B illustrates this display expansion. The marker
sweep need not be within the start-stop sweep. Thus the
start-stop sweep can be set to cover one range, such as the
passband of a filter, and the marker sweep can be set to
cover another range, such as the stop band.
Besides sweeping from a start frequency to a stop fre-
quency, the 8690's provide a calibrated narrow-band sweep
which is symmetrical about a center frequency. Simply
press the .!lF button, set the center frequency with the Start-
CW control, and adjust the deviation with the Stop-LlF
control. Total swing is indicated on the bottom slide-rule
)
)
Advertisement
