Why does the noise value reported by the marker in the spectrum analyzer display of my YBT250 disagree with the value reported by the Noise Floor measurement in the radio button 3 (interference package) by as much as 20 dB?

Question:

Why does the noise value reported by the marker in the spectrum analyzer display of my YBT250 disagree with the value reported by the Noise Floor measurement in the radio button 3 (interference package) by as much as 20 dB?

Answer:

The noise marker in the spectrum display is showing the noise in a Resolution Bandwidth Filter, which is automatically selected based on the span setting on the spectrum display. (This number can be found in the Edit menu, the spectrum tab).

The Noise Floor display (in the radio button 3 selection) is showing the noise number integrated across the channel bandwidth of the signal standard selected (as it appears in the upper left corner of the display). This could be as wide as 5 MHz for standards such as WCDMA (UMTS), while the spectrum display may be using a 30 kHz wide Resolution Bandwidth Filter if the span is set to 5 MHz. That means about 22 dB less noise is seen through this 30 KHz filter compared to the UMTS standard 5 MHz channel bandwidth. The same concept applies to each cellular standard with differing bandwidths such as 1.23 MHz for CDMA, 200 kHz for GSM/EDGE, 25 kHz for SMR, etc.

 

FAQ ID : 55156

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