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Forward and reverse measurements by amplifying the
source signal
Access to the RF path between the source and
the transfer switch allows the source signal to be
amplified and then be switched between port 1 or
port 2, allowing forward and reverse high-power
measurements. The input of the booster amplifier
connects to the "RF out" connector on the analyzer,
and the output of the booster amplifier connects
to the coupler. The coupled arm of the coupler
connects to the R-channel input to provide the
reference signal used for ratioing. To insure an
optimum power level at the R receiver, add any
needed attenuation between the reference coupler
and the analyzer. The optimum power range for the
receiver is provided by Agilent. The through arm
of the coupler connects to the "RF in" connector
on the analyzer. The amplified signal goes through
the transfer switch, which directs it to either test
port. Jumpers between the transfer switch and
the test ports give access to the RF signal path.
They allow the user to add high-power isolators
to protect the transfer switch. Without isolators,
signals with too much power can damage the
transfer switch. Isolators on both sides of the
transfer switch ensure that after the signal has
been measured by the coupler any signal will be
terminated, thereby protecting the switch.
Protecting the receivers
The final feature of this high-power option is the
internally controlled step attenuators that protect
the receivers. Located after the couplers and
before the receivers, these 55-dB step attenuators
(with 5-dB increments) reduce the signal to an
optimum level for the receiver. These attenuators
are controlled from the front panel of the analyzer.
Calibration
A major benefit of this configuration, besides the
ability to do both forward and reverse measure-
ments, is the ability to do full two-port vector error
correction. Calibrating in this manner takes into
account the effects of the hardware that has been
added to the setup (isolators, amplifiers, couplers,
etc.) and all errors associated with the analyzer
and the measurement setup up to the point of
calibration. Perform the calibration at the point
where the DUT will be connected.
When using this configuration, it is extremely
important not to damage any of the internal
components because high power levels are inside
the analyzer itself. Since amplification takes place
before the transfer switch, the power-handling
capabilities of the switch must be known. Analyzers
that allow signal amplification before the transfer
switch must specify how much power the switch
can handle. Agilent specifies maximum power for
the transfer switch for two conditions, when the
switch is switching, and when the switch is not
switching. Typically the nonswitching power-rating
is higher than the switching power rating. The
power-handling capability of all components in
the RF path must be considered when making
high-power measurements. When using this
configuration, it is important to understand
how the analyzer works and the power-handling
capability of each component in the signal path.
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