What is a dB, dBm, dBu, dBc, (Tutorial Videos from W2AEW on Youtube)

If the concept of decibels (dB) is confusing, this Youtube video from W2AEW has a very clear explanation with a demonstration using a spectrum analyzer:

• What is a dB, dBm, dBu, dBc, etc. on a Spectrum Analyzer?

https://www.youtube.com/watch?v=1mulRI-EZ80#aid=P-LGfIJuuH8

Remember: dB is a ratio of Power levels, so when you need to do a ratio of Voltages, the formula is different.  He doesn't mention that until late in the video.  However, he gives a much clearer explanation of why the formula is different (20 x Log10() vs 10 x Log10()) by doing the
math to demonstrate where the difference comes from.

(Remember P=I x E or P = (V^{^2})/R ?)

There is a table at the beginning of the video of the few things you should memorize both for your amateur radio test and for general use later:

• 3 dB represents a ratio that is a doubling.  Of the two things being compared, one has twice as much power as the reference.
• -3 dB represents a ratio that is a half.
• 10 dB is 10 times greater.
• 20 dB is 100 times greater.

Note: W2AEW has posted a whole bunch of good video tutorials on electronics and radio.

https://www.youtube.com/user/w2aew

A couple that might be relevant to prepping for your General Class amateur radio exam:

• Back to Basics: Voltage and Current in Capacitors and Inductors
• Basics of RF Mixers in Radio Receivers / Mixer Tutorial / Frequency Conversion

I've also found his oscilloscope and spectrum analyzer tutorials to be very useful.  He's very good at explaining and documenting things.  Compared to a normal text presentation, the demonstrations / experiments really drive the concepts home and show that it's possible to try these things for yourself.

Enjoy.

 

Learning to Program / Learning Python.

This post is a summary of some of the responses I've sent to people about learning to program computers as well as learning the Python programming language:

I've heard good things about the book, "Hello World! Computer Programming for Kids and Other Beginners", It's a first book on programming using Python. While it appears to be aimed at kids, I've heard some adults have found it to be a good gentle introduction as well.

•  Amazon: Hello World! Computer Programming for Kids and Other Beginners

See my other post about free on-line college level classes, for info on Computer Science 101.  This class is due to start April 23rd, 2012.  Hopefully it will be a good resource for people with no formal CS background.

The same professor, Nick Parlante, developed a class on Python for Google:

"Welcome to Google's Python Class -- this is a free class for people with a little bit of programming experience who want to learn Python. The class includes written materials, lecture videos, and lots of code exercises to practice Python coding."

• http://code.google.com/edu/languages/google-python-class/

There are a number of resources for programmers who know other languages to learn Python.  These include:

• Mark Pilgrim's Dive Into Python, and Dive Into Python 3, which are both available freely on-line, or can be purchased as regular print books. The original DiveIntoPython.Org site seems to have been pulled down. I'm not sure what's going on with this. This book seems to be a good intro for programers, though there are some experienced Python People who feel there are some problems with this work.
• The Python Wiki has a good list of Python for Programmer resources.
• The Python Tutorial on the main Python Documentation (docs.python.org) site is also pretty good.

Free on-line college-level computer science classes.

What do you want to learn today?
Starting last fall, Standford University made three college level computer science classes available on-line for free covering Databases, Artificial Intelligence, and Machine learning. These are actual courses with a set schedule, video lectures, graded assignments and quizzes. Previously lectures and course materials had been made available freely on-line. However, this is one of the first attempts to offer a full, structured course.
I followed along with the database class since I never took a formal class in databases. I was extremely impressed with: the format, the experience, and the potential for change. I was also incredibly impressed with Prof Widom, who appears to have a true gift for being an educator. She makes the delivery of the class seem effortless, which belies the enormous number of hours that must have gone into producing the course materials.
A good overview is Professor Widom's blog post:

• From 100 to 100,000 Students

There is now a for-profit company, Coursera, that is commercializing this style of on-line learning. There is now for Spring 2012, a much wider range of classes available.
Armando Fox and David Patterson delivered a very ambitious class on Software-as-a-Service (SaaS), that provides a slice across agile software engineering, web development using Ruby-on-Rails, cloud based deployments and many software engineering tools. It aims to take students through a very fast paced, realistic slice of a complete development experience. This is opposed to the traditional method of teaching one technology, one silo, at a time. It's still early to tell, but I suspect students who learn this way will be much more productive developers, much sooner.

• SaaS Class: http://www.saas-class.org/

Professors Fox and Patterson are developing a book, Engineering Long-Lasting Software: An Agile Approach Using SaaS and Cloud Computing that covers this slice of topics. The book is in the alpha stages now. I recommend reading at least the free sample chapter and preface. They've reviewed over 60 books on agile, ruby, rails, etc. in order to come up with the material for the course and book. The first run of the class was in March 2012. They are going to do a second run in May 2012.
A Computer Science 101 class is to start April 23rd, 2012. The class is taught by Professor Nick Parlante. I've recommended it to a number of people with no previous computer science background. The class will be using a simplified version of javascript and browser tools. I'll be following the feed back from the people I've recommended it to.

• Computer Science 101 - http://cs101-class.org/

Not to be left out, MIT is also offering a free course in electronics via MITX: MIT's new on-line learning initiative. While I'm interested in learning as much as I can about electronics, I decided not to try this course after reading the prerequisites. This appears to be a very formal class in the theory that's very heavy on math and physics. I unfortunately don't have a good math background.

• MITX: 6.002 - Circuits and Electronics

When talking about free on-line learning, it is also worth mentioning the very impressive Khan Academy. Wikipedia's description:

The Khan Academy is a non-profit educational organization, created by American educator Salman Khan. With the stated mission of "providing a high quality education to anyone, anywhere", the website supplies a free online collection of more than 3,100 micro lectures via video tutorials stored on YouTube teaching mathematics, history, healthcare and medicine, finance, physics, chemistry, biology, astronomy, economics, cosmology, organic chemistry, American civics, art history, microeconomics and computer science."

• The Khan Academy

While this is all very exciting now, it will be interesting to look back five to ten years from now to see what the effects of the wealth of free learning materials will be.