Keysight E6640A, Руководство пользователя и программиста по приложениям измерений

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4 Input/Output Functions
Input/Output
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 the 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 that 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 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
Input/Output
Couplings 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.
Readback 1-of-N selection | [variable]
Initial S/W Revision Prior to A.02.00
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.)
Note that the Ref Lvl Offset and Maximum Mixer Level are described in the Amplitude section. They are
reset by the instrument Preset. The External Preamp Gain is reset by the "Restore Input/Output Defaults"
or "Restore System Defaults->All functions. . The External Gain is subtracted from the amplitude readout
so that the displayed signal level represents the signal level at the output of the device-under-test, which
is the input of the external device that is providing gain or loss.
"More Information" on page 196
Key Path
Input/Output, External Gain
W-CDMA & HSPA Measurement Applications Reference 195