Sa Mode; Power Meter Mode - Keysight N9912A Service Manual

RF Analyzer Theory of Operation
N9912A Operation in Modes
The RF In Atten is not under user control. For a given frequency, the ADC Overload Adjustment determines
the setting for this attenuator to prevent over-range warnings.
There is no default calibration for two port measurements. Uncalibrated (not normalized) measurement of a
short thru cable typically shows a trace with some sawtooth characteristics.
SA adjustment results are ignored when in CAT/NA mode. T he "raw" unadjusted readings are used. There
is one exception: the results of the IF Offset Adjustment are used during CAT/NA modes.

SA Mode

The signal path for SA mode is the same as the input path for two port CAT/NA modes.
The RF In Atten can be set to 32 different levels: nominal 0 through 31 dB in 1 dB steps. The Attenuator
Slope Adjustment determines the correction factors for each step in each frequency band.
The RF In Atten can be controlled manually or automatically. When in auto mode, the Reference Level
setting determines the attenuator setting.
The Pre-amp can be in or out. Nominal gain of the pre-amp is 22 dB.
The "Attn" and "PA" indicators in the display header give current status. The Scale/Amptd hard key
provides access to control for them.
The displayed measured value for a given signal is automatically compensated for in the current Attn and PA
settings. For instance, if an incoming signal is measured at -70 dBm with the RF IN Atten set to 5 dB and PA
"out", changing to PA "in" will give a measured value of approximately -70 (+/- because the 22 dB for the
PA is only nominal). The difference seen in the trace will be that the noise floor of the trace will be lowered
by approximately 22 dB. If the RF In Atten is changed from 5 dB to 15 dB, the measured value will not change
significantly (still approximately -70 dBm) but the noise floor will raise by 10 dB.
SA has two basic modes: step and FFT.
Step mode reads a narrow slice of the spectrum and the LO steps for each slice. In this mode, a trace on the
display is composed from multiple slices. Generally spans greater than 100 kHz operate in step mode.
FFT mode reads a wide slice of the spectrum and the LO is fixed. In this mode, a trace on the display is based
on a single LO setting.
The LO minimum step size is 2 MHz; this restriction limits spurs.
The hardware operation of the A/D's is essentially the same for both step and FFT modes. The difference is
the digital signal processing.
The SA adjustments generally correct the gain with 11 frequency bands. See "SA Frequency Bands" on
page 5-10 for a listing of the 11 bands. See the TME help file for details on SA adjustments.

Power Meter Mode

All measurement circuitry is switched to the low power state during PM (power meter) mode. This is the
mode with the lowest power dissipation.
The analyzer has no power output capability in this mode. The analyzer essentially functions as a display for
a USB power sensor.
Service Guide N9912-90003 5-23