Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Forums Magazine Sponsor RF Cafe RF Electronics Symbols for Visio RF Electronics Symbols for Office Word RF Electronics Stencils for Visio Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Anritsu Alliance Test Equipment Amplifier Solutions Anatech Electronics Axiom Test Equipment Berkeley Nucleonics Bittele Centric RF Conduct RF Copper Mountain Technologies Empower RF everything RF Exodus Advanced Communications Innovative Power Products ISOTEC KR Filters Lotus Systems PCB Directory Rigol RF Superstore San Francisco Circuits Reactel RFCT TotalTemp Technologies Triad RF Systems Windfreak Technologies Withwave LadyBug Technologies Wireless Telecom Group Sponsorship Rates RF Cafe Software Resources Vintage Magazines Thank you for visiting RF Cafe!
Boonton RF Power Measurement

Amplifier noise figure - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2010 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

NOTICE: The original RF Cafe Forum is available again for reading, and the new RF Cafe Blog is an active board.

-- Amateur Radio

-- Anecdotes, Gripes, & Humor

-- Antennas

-- CAE, CAD, & Software

-- Circuits & Components

-- Employment & Interviews

-- Miscellany

-- Swap Shop

-- Systems

-- Test & Measurement

-- Webmaster

dohagan
 Post subject: Amplifier noise figure
Posted: Tue Feb 20, 2007 1:43 pm 
 
Captain
User avatar

Joined: Sat Mar 19, 2005 3:20 pm

Posts: 6

Hello,

I've got a variable gain amplifier connected directly to and Analogue-to-Digital converter (ADC). The input of the amplifier is terminated in 50 ohms and the gain is set to 20 dB. Measuring the noise at the output of the ADC (i.e. in Matlab) over a 200 kHz bandwidth, I get a value of -92 dB.

So, Pn = -92 dB = k+T+B+Fn+G

where Fn is the total noise figure of the system, G is the amplifier gain (20 dB) and B is the bandwidth (200 kHz).

I know the noise figure of the ADC itself to be 25.5 dB, but how do I find the exact value for the amplifier noise figure??

 
   
 
nubbage
 Post subject:
Posted: Wed Feb 21, 2007 4:23 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm

Posts: 343

Location: London UK

Hi

The overall noise factor of a 2 stage system will be dominated by that of the first stage, particularly, as in your case, where the first stage gain is 20dB.

First you have to convert dB NF to numerical NF (Fr), and dB gain to numerical gain (G, 100 in your case).

The overall NF is Fn = F1 +(Fr-1)/G

With G = 100, you can see the NF of the ADC has no importance, so Fn=F1.

The noise power into the ADC is just the expression you quoted, except Fn is the first stage NF, and the noise power is probably in dBW, depending on units used for the K value.

Inverting the expression then gives Fn.


 
   
 
sm7ovk
 Post subject:
Posted: Tue Feb 27, 2007 4:41 pm 
 
Captain
User avatar

Joined: Thu Jan 11, 2007 12:59 pm

Posts: 23

The formula is most often called Friis-formula, see more at www.producon.com/sm7ovk/friisformula.html

73

Jens, SM7OVK


 
   
 
OM
 Post subject:
Posted: Sun Aug 10, 2008 4:40 pm 
 
Lieutenant
User avatar

Joined: Sun Aug 10, 2008 3:41 pm

Posts: 3

To sm7ovk,

I regret to tell you that you are not right. You need to edit this page.

73!


 
   
 
smith08
 Post subject:
Posted: Tue Sep 30, 2008 1:10 am 
 
Lieutenant

Joined: Tue Sep 30, 2008 1:06 am

Posts: 1

where the signal to noise is measured by an ideal, noiseless receiver.

=====================

smith

Job Opportunities

Posted  11/12/2012

RF Electronics Shapes, Stencils for Office, Visio by RF Cafe
Berkeley Nucleonics Corporation - RF Cafe
Lotus Communication Systems Modular RF Component Building Blocks - RF Cafe

RF Electronics Shapes, Stencils for Office, Visio by RF Cafe

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free

 

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024

Webmaster:

    Kirt Blattenberger,

    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 World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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:

AirplanesAndRockets.com