Keysight N9912A - Preamplifier Control (Opt 235); Check for Compressed Measurements

Keysight N9912-90001 User’s Guide 8- 11
SA (Spectrum Analyzer) Mode
SA Mode Settings
—Press Scale/Amptd.
—Then RF Atten Auto Man
.
— Auto
RF Attenuation is set by adjusting the Reference Level. As the
Reference Level is lowered, for example from –10 dBm to –30 dBm, the
FieldFox assumes that you are looking at low-level signals. The RF
Attenuation value is automatically lowered in 5 dB steps to allow low-level
signals to be viewed. The RF Attenuation value is never automatically
lowered below 5 dB.
— Man
RF Attenuation is set manually. Enter a value between 0 to 30 dB in 5
dB steps using the numeric keypad, the arrows, or the rotary knob.
Then press Enter
.
#Atten xx dB is shown at the top of the screen. (#) means manual setting.
Preamplifier Control (Opt 235)
When very low-level signals are analyzed, an internal preamplifier can be used
to boost the signal level by approximately 22 dB. The gain of the preamp is
NOT adjustable. The displayed signal level is automatically adjusted for the
increase in system gain.
How to control the Preamp
By default, the preamp is OFF.
—Press Scale/Amptd
.
—Then Preamp ON
OFF. The underlined setting is the current setting. When
ON, PA is shown to the left of the graticules on the display.
Check for Compressed Measurements
Compression occurs when too much power into an amplifier causes it to no
longer amplify in a linear manner. When too much power goes into the
FieldFox RF Input connector, the amplifiers in the SA receiver compress and
signal power will not be displayed accurately. This can occur even if ADC Over
Range is not displayed because devices other than the ADC, such as the mixer,
might be compressed. Increase the RF Attenuation value to prevent the SA
receiver from being compressed.
How to Check for a Compressed Measurement
— Using a marker at the signal peak, make note of the signal power level.
— Increase the RF Attenuation level by 5 dB.
—If the signal level does NOT change, then NO compression exists. This
indicates that the signal is in the linear region of the FieldFox
receiver.