External Gain - Agilent Technologies X Series Manual

Example
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External Gain

Compensates for gain or loss in the measurement system outside the spectrum analyzer. The External
Gain is subtracted from the amplitude readout (or the loss is added to the amplitude readout). So, the
displayed signal level represents the signal level at the output of the device-under-test, which can be the
input of an external device that provides gain or loss.
Entering an External Gain value does not affect the Reference Level, therefore the trace position on
screen changes, as do all of values represented by the trace data. Thus, the values of exported trace data,
queried trace data, marker amplitudes, trace data used in calculations such as N dB points, trace math,
peak threshold, etc., are all affected by External Gain. Changing the External Gain, even on a trace which
is not updating, will immediately change all of the above, without new data needing to be taken.
Changing the External Gain causes the analyzer to immediately stop the current
NOTE
sweep and prepare to begin a new sweep. The data will not change until the trace
data updates because the offset is applied to the data as it is taken. If a trace is
exported with a nonzero External Gain, the exported data will contain the trace
data with the offset applied.
In the Spectrum Analyzer mode, a Preamp is the common external device providing gain or loss. In a
measurement application mode like GSM or W-CDMA, the gain or loss could be from a BTS (Base
Transceiver Station) or an MS (Mobile Station). So in the Spectrum Analyzer mode MS and BTS would
be grayed out and the only choice would be Ext Preamp. Similarly in some of the digital
communications applications, Ext Preamp will be grayed out and you would have a choice of MS or
BTS.
Key Path
Couplings
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Ext Preamp
This function is similar to the reference level offset function. Both affect the displayed signal level. Ref
Lvl Offset is a mathematical offset only, no analyzer configuration is affected. Ext Preamp gain is used
when determining the auto-coupled value of the Attenuator. The External Gain value and the Maximum
Mixer Level settings are both part of the automatic setting equation for the RF attenuation setting. (10 dB
of Attenuation is added for every 10 dB of External Gain.)
:FEED:AREF OFF
Off
Prior to A.02.00
Input/Output
The Ext Preamp, MS, and BS keys may be grayed out depending on which
measurement is currently selected. If any of the grayed out keys are pressed,
or the equivalent SCPI command is sent, an advisory message is generated.
1-of-N selection | [variable]
Prior to A.02.00
Input/Output
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