Ceyear 4041 Series, User Manual

Page: 49 / 203

Chapter IV Spectrum Analyzer Mode
37
c) Place the marker at the signal peak position, and then place the detla marker at the noise position whose
frequency offset is 200 kHz:
Press
【
Peak
】
, [Peak Search].
Press
【
Marker
】
, [Delta], 200 [kHz].
d) Activate the noise marker function to observe the signal to noise ratio:
Press
【
Marker
】
, [Marker Noise Off On]. See Fig 4-10.
The read signal to noise ratio is indicated in dB/Hz, because this noise vale is a noise bandwidth value normalized
to 1 Hz. This value decreases by decrements of 10×log (BW). If noise values at different channel bandwidths are
required, the measurement results will be corrected according to the current bandwidth. For example, if the data
read by the spectrum analyzer is -85dB/Hz, and the current channel bandwidth is 30 kHz, the signal to noise ratio
should be:
S/N=85dB/Hz - 10×log (30 kHz)=40.2 dB/(30 kHz)
At this time, if the differential marker is less than 1/4 of the distance from the signal peak to the edge of response,
the noise measurement will have potential errors.
Fig 4-10 Measurement of signal to noise ratio
3) Noise measurement by using the noise marker function
This instance will use the noise marker function to measure the noise of 1 Hz bandwidth by a 1 GHz external
signal.
a) Set the signal generator output signal:
Set the signal generator frequency at 1 GHz and signal power at -10 dBm, connect the signal generator output to
the input port of spectrum analyzer, and turn on the RF switch.
b) Set the center frequency, span, reference level and attenuator.