Rohde & Schwarz R&S FSP Series, Operating Manual

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R&S FSP Getting Started
Noise Measurements
2.16 Operating Manual 1164.4556.12 - 06
Determining the noise figure:
The noise figure of amplifiers or of the R&S FSP alone can be obtained from the
noise power display. Based on the known thermal noise power of a 50
Ω
resistor at
room temperature (-174 dBm (1Hz)) and the measured noise power P
noise
the noise
figure (NF) is obtained as follows:
NF = P
noise
+ 174 – g,
where g = gain of DUT in dB
Example:
The measured internal noise power of the R&S FSP at an attenuation of 0 dB is
found to be –153 dBm/1 Hz. The noise figure of the R&S FSP is obtained as follows
NF = -153 + 174 = 19 dB
Fig. 2.15 Correction factor for measured noise power as a function of the ratio of total power to
the intrinsic noise power of the R&S FSP.
If noise power is measured at the output of an amplifier, for example, the sum of
the internal noise power and the noise power at the output of the DUT is mea-
sured. The noise power of the DUT can be obtained by subtracting the internal
noise power from the total power (subtraction of linear noise powers). By means
of the following diagram, the noise level of the DUT can be estimated from the
level difference between the total and the internal noise level.
Correction factor in dB
Total power/intrinsic noise power in dB