Rohde & Schwarz R&S FSH6 - Determining the Reference; DIGITAL Tx Mode

R&S FSH Measuring the Carrier-to-Noise Ratio
1145.5973.12 4.51 E-11
The major measurement parameter settings are
available directly in the main menu of the carrier/noise
measurement or can be entered using the
corresponding function keys.
Determining the reference
Before the carrier-to-noise power ratio can be determined, the reference power or the reference level
must be specified. To specify the reference, the R&S FSH offers four possibilities: the DIGITAL Tx,
ANALOG TV, or CW Tx operating modes as well as manual reference. Enter the reference channel and
the channel bandwidth of the reference channel to measure the reference. To indicate that the
reference measurement has been activated, the REF MEASURE softkey is highlighted in green.
DIGITAL Tx mode
In the Digital Tx operating mode, the channel power of a reference channel is selectively measured. It is
then used as a carrier power (reference) for determining the carrier-to-noise ratio.
The settings for span, resolution bandwidth, video bandwidth and sweep time are coupled to the
channel bandwidth and are optimally set by the R&S FSH.
If you want to change the settings, note the following:
• The span is preset to 1.2 times the reference channel bandwidth. The span is always coupled to the
channel bandwidth. When changes are made, the R&S FSH automatically sets the appropriate
span.
• The resolution bandwidth should be between 1% and 4% of the channel bandwidth. This ensures
that the channel power is measured with good selectivity with respect to adjacent channels.
• The video bandwidth must be at least three times the resolution bandwidth. This prevents incorrect
results due to the compression of signal peaks by the video filter.
• The RMS detector is recommended. It ensures that the power is always correctly measured
irrespective of the waveform to be measured.
• Set the sweep time in such a way that the result is stable. If the sweep time is extended, the
R&S FSH also increases the integration time for the RMS detector, thus yielding measured values
that are more stable.
 Press the SELECT MEASURE softkey.
The menu for selecting the reference measurement
opens.
 Using the rotary knob or the cursor keys, select
DIGITAL Tx and confirm your choice with the
ENTER key or the F1 softkey.
The R&S FSH starts the DIGITAL Tx reference
measurement. C/N-DTx is inserted in the top right-
hand corner of the display. The reference channel and
the channel bandwidth are set in accordance with the
last DIGITAL Tx reference measurement.