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I just realized the wrong file was pointed to for episode 43, it actually pointed to episode 9. Sorry about that. Here is episode 43 again, with the correct file. I am currently shooting Episode 44, so look for that soon.
Example Blackbody Source - Image via Wikipedia
In this episode the topic of blackbody or thermal radiation is discussed. This is a connection between radiometry and photometry and temperature measurement. Discussed are blackbodies and what are called greybodies (blackbodies with emissivities < 0.99) Blackbody and greybody sources are used in the calibration of radiometric devices. The sun, stars, and the whole universe emit spectra consistent with a blackbody spectrum, as does every body at finite temperature. This is why one can measure temperature approximately by observing the electromagnetic radiation emitted from matter.
The spectral radiance (power radiated per unit area per unit solid angle per unit wavelength) of a blackbody is goverened by what is called Planck’s law:
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This can be integrated to give the total radiant exitance (power radiated per unit area) F=σT4.
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Episode 42 - Life, the Universe, and Radiometry?: Play Now | Play in Popup | Download (304)This is our latest podcast on the subject of Radiometry. It has been awhile since our last podcast, and in this podcast I explain what is going on. I recorded this twice, and used footage from both attempts, but I am not perfectly happy with the result, but it has been awhile so I decided to put it up anyway.
The first two volumes of our measurement series have just been published:
These are the first two books in a series of eight books that we are planning to publish, built primarily from our online material.
In this episode we go over some basics S-parameter measurement. These include a description of a type of directional coupler, the basic concept of how to represent a reflectometer as a two-port device, and finally how to calibrate the associated model parameters using an open short and load. The measurements of a two-port device are then briefly discussed, by adding a through measurement to the calibration. Isolation terms in the calibration are not discussed.
This episode has a few mistakes in it, but those were basically corrected by putting notations on the video. I didn’t want to reshoot a third time to correct them. This episode is heavy on the mathematics of reflectometer calibration, and gives approximate calibration equations that one could use if they wanted to construct their own reflectometer. What is not covered is that there are some problems that need to be considered. The main idea shown here is that it is possible to compensate for errors in a reflectometer or network analyzer with some simple measurements of an open, short, and load.
The following course has been added to the course catalog
This is the fourth of a series of four courses on MIL-STD-461 measurements. The topic of this course is radiated susceptibility, or RS measurements.
This is the first in a series of podcasts on the subject of RF and microwave measurement. In this episode we reintroduce S-parameters, and give some of the basic equations for cascading a two-port and a one-port or two-port. S-parameters come from a concept that was borrowed from particle physics by electrical engineers to solve the problem of propagation of RF signals through a network. A network is anything that has ports where signals can be input and output, if there are N of these ports, there are N2 of these S-parameters.
If there is an wave amplitude input at port n of an, and and output of wave amplitude bm at port m, then
Smn = bm / an
There were several courses introduced into the LearningMeasure.com course catalog since the last podcast. These are
If these, or any of the other courses in our course catalog, interest you, please register as a student and subscribe. It is your subscriptions that keep this podcast going!
As always, let us know if there is any topic you want to see covered on the podcast, or if there is any course you would like to see developed.
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