----- Original Message ----- From: "Joe Leikhim" <rhyol...@nettally.com> To: "amsat-bb@AMSAT.Org" <amsat-bb@amsat.org> Sent: Thursday, January 17, 2013 5:52 PM Subject: [amsat-bb] NIST Phase Noise Measurements Group Noise Figure kTBcorrection
> This came to my attention yesterday. > > NIST presents interesting 3 dB correction to historic value assumed > for kTB to -177 dBm/Hz . I always assumed -174 dBm/Hz based on past > publications. > > http://tf.nist.gov/phase/noisemeas.html > > I wonder how this affects metrology and calibration of noise figure meters? > -- > Joe Leikhim > Leikhim and Associates > Communications Consultants > Oviedo, Florida > jleik...@leikhim.com > 407-982-0446 > WWW.LEIKHIM.COM > Hi Joe, The KTB = -174 dBm/Hz noise floor is based on K= Boltzmann constant = 1.38 x 10^-23 joule / kelvin T = 290 degrees kelvin as internationally stated as room temperature by Friis and so KTB = 1.38 x 10^-23 x 290 x 1 = 4.002^ -21 watt/Hz 10 log ( 4.002^ -21) = -203.977 dBW / Hz 10 -203.977 + 30 = -173.977 dBm/Hz (or approx -174 dBm/Hz) Actually all Noise Sources heads of the instruments to calibrate the value of Noise Figure NF in dB are based on Noise Excess referred to room temperature of 290 degrees kelvin or +17°C It comes that if KTB is changed from -174 dBm/Hz to -177 dBm/Hz than the standard room temperature of 290 kelvin (+17°C) must be changed to 140 kelvin ( - 133 °C ) wich is a not practical temperature to be managed in any measurement laboratory. and infact: KTB = 1.38 x 10^-23 x 140 x 1 = 1.932^ -21 watt/Hz 10 log ( 1.932^ -21) = -207.139 dBW / Hz 10 -207.139 +30 = -177.139 dBm /Hz (or approx -177 dBm/Hz ) At this point all Noise Sources heads of the instruments to calibrate the value of Noise Figure NF in dB and Noise Excess must be changed from 290 to 140 degrees kelvin and this will strongly AFFECT METROLOGY AND CALIBRATION of all noise figure meters. If you actually have a preamplifier with a Noise Figure of 3 dB than it's Noise Factor F = 10^ (NF/10 ) = 10^(3/10) = 1.99 If you actually want to know how many kelvin correspond a Noise Temperature T for a Noise Factor = 1.99, than T = (1.995 -1) x 290 = 288.62 kelvin On the other side referring T to 140 kelvin instead of 290 kelvin than a Noise Figure of 3 dB will correspond to a Noise Temperature of T = (1.995 -1) x 140 = 139.33 kelvin. Best 73" de i8CVS Domenico _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
