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

Noise Figure Measurement??? - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


 Post subject: Noise Figure Measurement???
Posted: Wed Sep 06, 2006 11:41 am 
 
Captain
User avatar

Joined: Wed Jan 05, 2005 2:20 am
Posts: 13
Location: BeiJing,China
Today, I tried to measure the NF of RF power amplifer with Aglient Spectrum analyzer and Signal generator. I know there is three ways to measure NF,
1. use NF analyzer (I don't have one)
2. Q-factor (I don't have two noise source)
3. Gain method. NF = Pn(tot)@output+174dbm-Gain

The problem as following,
1. The Pn(tot)@output is ~-70dbm[pwr in 0dBm, Gain(RFPout-RFPin):32dB, PA is working(Vcc(3.5v), Vpc(2.2v, 25%DC)), center frequency 1710MHz]. So base on the result, the NF of PA should be ~68dB:-(. it is impossible.

My question are
1. Did I do something wrong during test NF?
2. Did the formula right for cal NF by Gain method?
3. Do I need to set the fixed RBW for Spectrum Analyzer? Is there any relationship between NF and RBW setting for SpecAnalyzer?
4. Could anyone provide me some other ways to test it with my available equipment? as well as any helpful appnote.

8) Simon Liu


 
   
 
 Post subject:
Posted: Wed Sep 06, 2006 3:20 pm 
 
Captain
User avatar

Joined: Sun May 14, 2006 8:53 pm
Posts: 20
Location: Earth
First let me correct one statement:
Quote:
2. Q-factor (I don't have two noise source)

This should be Y-factor.

I was going to mention that to use the last method (which you call Gain Method) you have to make sure you're most definitely above the Analyzer Noise Floor. But it seems that in your application (PA) you may well be.

With this said, this is how I would go by doing it:

    1) Set the analyzer to the proper settings (i.e. ref level, minimum required attenuation, freq span, RBW/VBW). Note that attenuation and frequency span will affect the analyzer noise floor (RBW/VBW will as well, but the Analyzer can take these effects out). So the narrower the freq span the better resolution you'll have and the lower the internal attenuation (this will be set by the incident power into the Analyzer) the better resolution as well.

    2) Look at the noise floor before and after transmission. You should see at least a 10dB jump while transmitting. This will indicate that the noise generated by the transmitter (i.e. noise you want to measure) is at least 10dB above the analyzer noise floor.

    3) Measure the noise power (Pn) while transmitting. Now you can use your equation, where the thermal noise power is -174dBm/Hz. Which means that you have to either state the measured noise power in a 1Hz BW, or state the thermal noise in the measured BW. To make it clearer, if your measuring BW (i.e. RBW) is 1kHz, the thermal noise will be 30dB higher (i.e. -174dBm/Hz + 10*log(1kHz) = -144dBm). Most Analyzers come with a noise marker which will allow you to measure noise power in a 1Hz BW directly, then you can apply your equation directly.

Note:
    1) A notch filter maybe useful to notch transmitter power and reduce level into Analyzer. This will allow to go with minimum attenuation (0dB?) which will give the best Analyzer noise floor (w/o the use of an external LNA).
    2) Remember when measuring noise to always list your measuring bandwidth.

Hope this helps.


 
   
 
 Post subject:
Posted: Wed Sep 06, 2006 10:20 pm 
 
Captain
User avatar

Joined: Wed Jan 05, 2005 2:20 am
Posts: 13
Location: BeiJing,China
Thanks


 
   
 
 Post subject:
Posted: Thu Sep 07, 2006 10:34 am 
 
Captain
User avatar

Joined: Wed Jan 05, 2005 2:20 am
Posts: 13
Location: BeiJing,China
I tried today, it can works.






Posted  11/12/2012
A Disruptive Web Presence

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

Read About RF Cafe
Webmaster: Kirt Blattenberger
    KB3UON

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