Keysight Technologies C Series - Preamplifier Control (Opt 235); Check for Compressed Measurements

Keysight N9915-90020 User’s Guide 263
RTSA (Real-time Spectrum Analyzer) Mode—Option 350
RTSA Mode Settings
— Auto RF Attenuation is set by adjusting the acquisition. As the acquisition is
lowered, for example from –10 dBm to –40 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.
—
Man RF Attenuation is set manually. Enter a value between 0 to 40 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 15 to 20 dB (depending on model).
The gain of the preamp is NOT adjustable. The displayed signal level is
automatically adjusted for the increase in system gain, therefore turning the
Preamp ON should NOT cause a change to the displayed signal.
How to control the Preamp
By default, the preamp is OFF.
—Press Scale/Amptd
.
—
Preamp ON OFF When ON, PA is shown to the left of the graticules on the
display.
— Auto When Auto is selected, the preamp setting is coupled to the RF
attenuation and to the acquisition. When the acquisition reaches a certain
value, the preamp is turned on and
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 RTSA 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 RTSA
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.