RF Cafe Software
About RF Cafe
1996 - 2016
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
Try Using SEARCH
to Find What You Need.
There are 1,000s of Pages Indexed on RF Cafe !
Noise figure (NF) is the increase in noise power of a device from the input to the output that is greater than 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 (dB). Note: NF is not a power level, so it never has units of dBm.
As the following equation shows, cascaded noise figure is affected 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.
Cascading Noise Figure Values in a Chain of Components
Click here to view an example of a cascaded system.
Conversions: nf = 10NF/10 ↔ NF (dB) = 10 * log10 (nf)
where nf is a unitless ratio and NF has units of dB
This equation gives the method for calculating cascaded NF (nf) values based on the nf and gain of each stage. When using the formula in a software program or in a spreadsheet, it is more convenient and efficient to calculate each successive cascaded stage with the one preceding it using the following format, per the drawing (above-right).
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) =
Noise Figure (dB) =
These equations assume a room temperature reference (290 K). If applicable, use whatever your reference temperature is in place of the 290K shown.
Cascaded Noise Temperature Calculation
The following table lists a few conversions. See the Noise Power Calculator online calculator for calculating other values.