HIGH POWER NETWORK
ANALYZER
HP 8720B-H83
SERIAL NUMBER PREFIX
2909A AND ABOVE
MODIFICATION PART NO. USE THIS MODIFICATION
08720-90112 WITH MANUAL PART NO.
SEPTEMBER 1989 08720-90105
REV. 2PRINTED MAY 1989
HP 8720B-H83
Page 2 of 7
INTRODUCTION:
This manual insert describes the differences in the HP 8720B Option H83 High Power Network
Analyzer compared to the standard HP 8720B. It also describes the manual changes necessary to
document the HP 8720B-H83.
DESCRIPTION:
The HP 8720B Option H83 is a standard HP 8720B that has been modified to
permit higher power at the measurement ports. This is accomplished by inserting a high power
amplifier into the RF signal path through
connectors on the instrument rear panel. The instrument is shipped
from the factory with jumper cables installed on the rear panel connected in what is termed the "BYPASS" configuration (see Figure 2).
This will allow the instrument to be used with normal power levels
over a reduced frequency range. The reference channel (R) has
been brought out to the rear panel to allow the user to set the power
at the test ports as well as to make it possible to define a particular
reference configuration.
The HP 8720B Option H83 differs from the standard HP 8720B in that a
power splitter (with a 6 dB nominal loss) is replaced with a low loss
(<1 dB) directional coupler. Since couplers have limited
frequency response compared to power splitters, the frequency
range of the HP 8720B Option H83 in the "BYPASS" and "HIGH POWER"
configurations is degraded below 2 GHz. The unit operates like
a standard HP 8720B in the "TEST" configuration.
OPERATION:
* * * * * * * * * * * * * * CAUTION * * * * * * * * * * * * * * * *
* A high level RF signal may be present at the test ports on *
* retrace. Caution should be taken in testing active components. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
The ALC loop in the HP 8720B Option H83 is on during forward sweep
and levels the RF signal at the test ports. However, during retrace
the ALC loop is turned off by internal software and a fixed bias
current is injected into the source modulator. Depending on the
gain of the amplifier being used, a high level RF signal may be
present at the test ports during retrace (See HIGH POWER operation
for amplifier constraints). This is an important consideration
since excessive power can damage sensitive devices. The loss from
RF IN to PORT 1 typically increases from 1 dB at 2 GHz to 6.5 dB at
20 GHz. Also, excessive power will cause error messages to appear
on the analyzer display. These error messages will be of two types:
PHASE LOCK LOST and/or EXCESSIVE POWER AT THE TEST PORTS.
NOTE: The internal software has not been modified for this option
and the power levels indicated on the HP 8720B Option H83
may differ depending on which user configuration is chosen.
HP 8720B-H83
Page 3 of 7
OPERATION (continued):
The power appearing at the measurement channel is dependent on
the reflection coefficient of the load at the test port. During
error correction, with an open and/or a short connected, all power
is reflected and coupled back to the measurement channel through the
nominal 20 dB coupling factor. The overload error messages are designed to be enabled at nominally +3 dBm at the sampler (+23 dBm at
test ports). However, at levels exceeding -10 dBm (+10 dBm at test
ports) the sampler begins to limit. The minimum recommended power
level into REF IN is -20 dBm. Below this level the measurement is degraded due to noise. Additionally, internal service tests 21 and 22
may fail due to the extra cable loss of the HP 8720B Option H83.
The HP 8720B Option H83 can be configured in three different modes
of operation as described below. See Figure 2 for RF diagrams of each configuration.
BYPASS
Connect the supplied semi-rigid RF cables from RF OUT to RF IN and from REF OUT to REF
IN on the rear panel. The test port power
will be as displayed over the frequency range 2 GHz to 20 GHz.
The unit will continue to operate below 2 GHz but the test port
power will increase as frequency decreases. Also, the source may go
unleveled at the low end of the frequency range due to the ALC loop
running out of range. This configuration is not specified below 2 GHz.
HIGH POWER
Insert an external microwave amplifier (HP 8349B Option H83 or
equivalent) into the signal path as shown. Minimum lengths of high quality microwave cable
should be used since external cabling will
affect the power level at the test ports. The maximum recommended input power level that
should be applied to the HP 8720B-H83 is
+23 dBm. The unit can withstand a rear panel RF INPUT level of
+27 dBm without permanent degradation of performance. To provide
+10 dBm of power at the test ports the following external amplifier
considerations are given:
Minimum gain.............20 dB
Maximum gain.............28 dB
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