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The Signal Separation Device
The HP 11666A Reflectometer Bridge functions as a
signal separation device, separating the reflected from
the incident signal and permitting simultaneous trans-
mission
and reflection measurements.
It has an ex-
tremely broad, flat frequency response (0.04 to 18 GHz)
and it is very compact and rugged. Two Schottky diode
detectors are built into the 11666A, for the R and A
detector inputs of the 8755S. The 11666A may be used
alone for reflection-only measurements,
or with one
detector (HP 11664A) for simultaneous reflection and
transmission
measurements.
For
transmission-only
measurements,
a power splitter (HP 11667A)
and two
detectors (HP 11664A) may be substituted for the Bridge
yielding a cost savings and greater dynamic range.
The Source
The source for this system is the HP 8350A Sweep
Oscillator mainframe and the HP 83592A Plug-in. To-
gether they form a completely programmable sweeper
that can produce a +10 dBm signal over a frequency
range of 0.01 to 20 GHz. All controls and settings are
accessible through HP-IB commands: sweep mode, fre-
quency span, frequency markers, sweep time, and even
power level on the 83500 series Plug-ins. It also has a
27.8 kHz modulator built in, to provide the properly
modulated
RF test signal for the 8755S. The 8350A
mainframe may be used with any of the 83500 series
Plug-ins, or any of the 86200 series Plug-ins with an
HP
11869A
Adapter.
Some
plug-ins
produce
enough
power (+17 dBm) to take advantage of the full dynamic
range
of the 87555
even
when
system
losses
due
to
power splitters and bridges are included.
The A/D
Analog to digital conversion is performed by the HP
59313A A/D Converter. Four separate input channels
and an HP-IB interface make this A/D especially useful.
Each channel is independent and can be set for *1,
*2.5, %5, or =10 volts full scale. Within each range, the
59313A has 0.1% resolution.
The Controller
Instrument control, data computation, and output for
the system is provided by the economical HP 85A Com-
puting Controller. The HP 85A is a complete computer
with a CRT
screen, a full-size typewriter-style
key-
board, a 32-column thermal printer, and a 200K byte
tape cartridge drive built into a compact and attractive
desktop enclosure. The HP 85A programs in easy-to-
learn HP Enhanced BASIC
with special commands
for
graphics and HP-IB operations. The HP 85F, listed in
Table 1, provides system control with the HP 85A, the
HP-IB
Interface, and
the I/0 ROM
(these accessories
are required for the system).
SYSTEM
CONNECTION
Connect the system as shown in Figure 2 and set the
controls as follows:
CHANNEL
1
..
CHANNEL
2 ..
.
VERTICAL RESOLUTION
(dB/div)
.
REFERENCE OFFSET VERNIERS
...
REFERENCE
POSITION
LINE
......... see Operation
section of this note
.A/R
-B/R
.0.25,1, 5, or 10
HP 85A Controller
DUT
HP 11664A
Detector
Figure 2. Connection Diagram.
In this application, Channel 1 of the 87558 is used for
reflection measurements and Channel 2 is used for trans-
mission measurements. The vertical resolution (dB/DIV)
of the 87555 can be set to any value as long as both
channels are set the same. To prevent accidentally un-
calibrating the system during measurement, it is recom-
mended
that the Reference
Level Offset verniers
be
turned off before running the system. See the Operation
section
of this note
for instructions
on
setting
the
Reference Position line.
Make certain the HP-IB address of the 8350A sweeper
is set to 19 (decimal)
by pressing
SHIFT,
LCL
and
observing the HP-IB address that appears in the FRE-
QUENCY/TIME
display
on
the
8350A.
If the
HP-IB
address
is not 19, refer to the 8350A
Operating
and
Service Manual
for instructions on changing it.
Set the sensitivity of the 59313A A/D
so that chan-
nels 1 and 2 respond to =1 volt full scale and channels
3 and
4 respond
to =5
volts
full scale,
and
set
the
HP-IB address to 10 (decimal) according to the instruc-
tions in the 59313A Operating and Service Manual. The
A/D
must
be calibrated
before
making
any
measure-
ments, and should be recalibrated periodically. Refer to
Appendix II of this note for a calibration program and
instructions for using it.
The Select Code of the HP-IB Interface for the HP
85A (HP 82937A)
must be set to 7 (decimal). Refer to
the operating information supplied with the interface
for instructions.
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