Homepage - RF Cafe
Webmaster: Kirt Blattenberger | KB3UON | Sitemap | ©1996-2014     Visit RF Cafe on
      Menu below is just a small sample of what is here!          Visit RF Cafe on Facebook Visit RF Cafe on Twitter Visit RF Cafe on LinkedIn
Custom Search
More than 10,000 searchable pages indexed.
•−•  ••−•    −•−•  •−  ••−•  •
RF Cafe Morse Code >Hear It<

Cascaded Noise Figure & Noise Temperature

Noise figure is the increase in noise power of a device from the input to the output that is greater that the signal gain. In effect, it is the amount of decrease of the signal-to-noise ratio. Like gain, noise figure can be expressed either as a ratio or in decibels.

Example cascaded system - RF Cafe
Click here to view
an example of a
cascaded system.
Cascade noise figure calculation is carried out by dealing with gain and noise figure as a ratio rather than decibels, and then converting back to decibels at the end. As the following equation shows, cascaded noise figure is effected most profoundly by the noise figure of components closest to the input of the system as long as some positive gain exists in the cascade. If only loss exists in the cascade, then the cascaded noise figure equals the magnitude of the total loss. The following equation is used to calculate cascaded noise figure as a ratio based on ratio values for gain and noise figure (do not use decibel values).

Here is a  great article on Noise Figure Uncertainty in the October 1999 "Microwave & RF" magazine.

Note that when calculating cascaded noise figure, quantities must be expressed as ratios, NOT as decibels. By convention, lower case variables represent ratios, while upper case variables represent decibels (dB).

                     Conversions:   nf = 10NF/10     NF (dB) = 10 * log10 (nf)
In Compact Form:

nfN = Cascaded noise figure equation formula - RF Cafe, where N = number of stages
Cascaded Noise Figure In Expanded Form:

Cascaded noise figure equation - RF Cafe

Click here to see Agilent's App Note 1303 on using a spectrum analyzer
to measure noise figure.
Conversion Between Noise Figure and Noise Temperature

Noise Temperature (K) = 290 *Noise figure to noise temperature conversion equation formula - RF Cafe

Noise Figure (dB) = 10 * log10 Noise temperature to noise figure conversion equation - RF Cafe
These equations assume a room temperature reference (290 K).
If applicable, use whatever your reference temperature is in place of the 290.
Cascaded Noise Temperature Calculation

Cascaded noise temperature equation - RF Cafe

The following table lists a few conversions. See the Noise Power Calculator online calculator for calculating other values.

NF(dB) TN (°K)   NF(dB) TN (°K)
0.1 7 2.1 180
0.2 14 2.2 191
0.3 21 2.3 202
0.4 28 2.4 214
0.5 35 2.5 226
0.6 43 2.6 238
0.7 51 2.7 250
0.8 59 2.8 263
0.9 67 2.9 275
1.0 75 3.0 289
1.1 84 3.1 302
1.2 92 3.2 316
1.3 101 3.3 330
1.4 110 3.4 344
1.5 120 3.5 359
1.6 129 3.6 374
1.7 139 3.7 390
1.8 149 3.8 406
1.9 159 3.9 422
2.0 170 4.0 438
Noise figure equation - RF Cafe

Check this out - someone referenced this page on Wikipedia!

A Disruptive Web Presence

Custom Search
Over 10,000 pages indexed! (none duped or pirated)

Read About RF Cafe
Webmaster: Kirt Blattenberger

RF Cafe Software

RF Cascade Workbook
RF Cascade Workbook is a very extensive system cascaded component Excel workbook that includes the standard Gain, NF, IP2, IP3, Psat calculations, input & output VSWR, noise BW, min/max tolerance, DC power cauculations, graphing of all RF parameters, and has a graphical block diagram tool. An extensive User's Guide is also included. - Only $35.
RF system analysis including
frequency conversion & filters

RF & EE Symbols Word
RF Stencils for Visio

Product & Service Directory
Personally Selected Manufacturers
RF Cafe T-Shirts & Mugs

RF Cafe Software

Calculator Workbook
RF Workbench
Smith Chart™ for Visio
Smith Chart™ for Excel
Your RF Cafe Progenitor & Webmaster
Click here to read about RF CafeKirt Blattenberger... single-handedly redefining what an
                                 engineering website should be.

View the YouTube RF Cafe Intro Video Carpe Diem! (Seize the Day!)

5CCG (5th MOB): My USAF radar shop

Airplanes and Rockets: My personal hobby website

Equine Kingdom: My daughter Sally's horse riding website