1Measurement Example - Measuring The Level Of The Internal Reference Generator At Low S/N Ratios - Rohde & Schwarz R&S FSP Series Operating Manual

R&S FSP
RMS detector
For each pixel of the trace, the RMS detector outputs the RMS value of the IF enve-
lope for the frequency range assigned to each test point. It therefore measures
noise power. The display for small signals is, however, the sum of signal power and
noise power. For short sweep times, i.e. if only one uncorrelated sample value con-
tributes to the RMS value measurement, the RMS detector is equivalent to the sam-
ple detector. If the sweep time is longer, more and more uncorrelated RMS values
contribute to the RMS value measurement. The trace is, therefore, smoothed. The
level of sinewave signals is only displayed correctly if the selected resolution band-
width (RBW) is at least as wide as the frequency range which corresponds to a pixel
in the trace. At a resolution bandwidth of 1 MHz, this means that the maximum fre-
quency display range is 501 MHz.
Average detector
For each pixel of the trace, the average detector outputs the average value of the
linear IF envelope for the frequency range assigned to each test point. It therefore
measures the linear average noise. The level of sinewave signals is only displayed
correctly if the selected resolution bandwidth (RBW) is at least as wide as the fre-
quency range which corresponds to a pixel in the trace. At a resolution bandwidth of
1 MHz, this means the maximum frequency display range is 501 MHz.
Quasi peak detector
The quasi peak detector is a peak detector for EMI measurements with defined
charge and discharge times. These times are defined in CISPR 16, the standard for
equipment used to measure EMI emissions.
2.3.0.1 Measurement example – Measuring the level of the internal reference genera-
tor at low S/N ratios
The example shows the different factors influencing the S/N ratio.
1. Set the R&S FSP to its default state.
2. Switch on the internal reference generator
3. Set the center frequency to 128 MHz and the frequency span to 100 MHz.
4. Set the RF attenuation to 60 dB to attenuate the input signal or to increase
the intrinsic noise.
Operating Manual 1164.4556.12 - 06
Press the PRESET key.
The R&S FSP is in its default state.
Press the SETUP key.
Press the softkeys SERVICE - INPUT CAL.
The internal 128 MHz reference generator is on.
The R&S FSP's RF input is off.
Press the FREQ key and enter 128 MHz.
Press the SPAN key and enter 100 MHz.
Press the AMPT key.
Measuring Signals in the Vicinity of Noise
Getting Started
2.11