Good tutorial on Serial from Saleae (working with microcontrollers)

Here's a good tutorial on serial communications, particularly if you are working with microcontrollers.

• Learn Asynchronous Serial - http://support.saleae.com/hc/en-us/articles/200284509-Learn-Asynchronous-Serial

I want a Saleae Logic 8 for Christmas.  They look pretty neat.

Advice for Getting a Ham Radio (aka Amateur Radio Licnese)

[I wrote this somewhat long response to a question on a mailing list.  I'm sharing it here in case it will help anyone else.]


First, don't pick up a radio until you've passed your test.  It will be a distraction that will keep you from studying.  Plus, you are more likely to become frustrated with an un-programmed radio with no idea what frequencies to check for activity.  Amateur radio doesn't really have channels to flip through.

As far as passing the test, two ends of the spectrum have been mentioned so far, memorizing "flash cards" vs. reading the ARRL book cover to cover.
The first and second level exams are 35 question multiple-choice tests covering a bit of rules/regulations, operations practice, and a little bit of theory.  The complete set of questions that your 35 will be drawn from are published.  The question pool changes every four years and is freely available for download.

A fair number of the questions require memorization.  For example there are questions about what frequencies you can operate on. Once the material starts to sink in there will be more stuff that you just know because you understand it and not because you've memorized it, but being able to remember the frequencies remains.

The best way to prepare for your test depends on your goals and how you learn best.  If you like to read and want to learn, then reading the whole ARRL technician license guide (cover to cover) might be best for you.  Ideally, you want the most recent edition from 2014, that includes the new technician question pool that went into effect July 1, 2014.

If you want something a little more condensed and/or free, several people take the question pools and publish study guides with additional info to help you prepare for the test.  KB6NU makes his "No-Nonsense Study Guides" available in PDF here:   (Technician and General are free)

    http://www.kb6nu.com/tech-manual/

There are plenty of other resources including some audio podcasts that review the material for the test.  (There are probably lots of youtube videos as well, I haven't looked.)

The site that was previously mentioned hamexam.org is a great free place to review "flash cards" for the entire pool or take practice tests. It will keep track of what questions you've answered correctly.

    http://hamexam.org/

Go ahead, try some of the questions cold.  If you are a good multiple choice test taker with a bit of a technology background you might get half the questions right without studying.  The tests are not that
hard.  You can get 9 questions wrong and still pass the 35 question test.

There are several places locally where you can take the test.  There is a test session at Columbia University usually on the third Monday of every month.  The next one is December 15th, which gives you plenty of time to study .

    http://www.w2aee.columbia.edu/cuarc-exams.html

Many other test sessions can be found on the ARRL's site.  (Note: there may be exams offered by organizations that aren't affiliated with the ARRL that won't be listed there, like one of the clubs in Brooklyn.)

    http://www.arrl.org/find-an-amateur-radio-license-exam-session

Finally preparing for the test won't give you everything you need to know to be an effective radio operator.  However it's an important hurdle to just get over.   Once it's out of the way, there are plenty
of people who can help with all the practical "Radio 101" to fill in all the gaps.

Hope This Helps,
--Rob

Trying to get active again

Just noticed it's been six months since I've posted anything. 

Let me try to fix that.

Technology: It's Just a ... (Meaningful one of two sentence summaries)

One of the frustrating experiences in technology is trying to find out what some new thing is really all about and where it fits in. You can read tons of marketing materials and still not got the gist. Then sometime later when you are talking to someone else (with a deep technical background) who is familiar with the new thing, they say "Oh, it's just a foo with bar" or "It's similar to foo but does bar" and that causes a lightbulb to go off and you just grok what the new thing is and where it fits in.

I had one of those moments today, Slightly buried in the FAQ, for Red Hat buying Inktank, there was this two sentence summary that makes the relationship between Gluster and Ceph/Inktank clear:

Inktank has a more mature block interface and OpenStack integration, while Gluster has a more mature file system interface and traditional web storage integration. Therefore, the two complement each other very well and we believe the combination is a very attractive alternative to traditional proprietary storage.

To me, that was the Ah-Ha! description that I needed.   Sometimes I wish there was a place that had these sort of short nutshell summaries that was written by technical people for technical people.

Linux Trivia: Grub Legacy 128 byte inode dependency

Documenting something that I tripped over while trying to fix a very old Linux system. 

Grub Legacy (0.97) is dependent on 128 byte inode sizes.  Newer systems use 256 byte inodes to store extended attributes.  This confuses grub causing it not to be able to boot system as well as cause boot loader installation to fail with odd error messages like can find /boot/grub/stage1.

Fortunately googling found that Kristian Reese had documented this in his own "knowledge base", somewhat like I'm doing here in a less organized fashion.

The file /boot/grub/stage1 not read correctly kristianreese.com knowledge base

The solution is to use mke2fs ... -I 128 ...to force a 128 byte inode size when re-making the "legacy" root file system that will be booted by grub "legacy".

Use tune2fs -l /dev/foo to see the current file system parameters.  Tip: Save tune2fs dump info someplace for import (root) file systems someplace off the system.

Cool Technology: IPython Notebooks

I may be very late to the party but I've recently discovered IPython notebooks.  IPython is an extremely useful Python shell environment that has been kicking around for 10+ years. Initially the number of advantages it offered over the built-in python shell was small.  But then again it started out as a couple of hundred line hack.  So back then it seemed like it wasn't worth the trouble to make sure it was install on all the machines you might hack Python on.

Fast forward to 2010 or so, IPython has reached a 1.0 milestone, and has evolved significantly to an extremely powerful platform.  However the aspect that I find the most useful is notebooks that display in a web browser.   It's supposed to be somewhat reminiscent of Mathematica which I've never used.

Notebooks contain blocks of executable Python code and their output.  The Python code can be edited and run/rerun right there from the browser.  But where it really gets interesting is that rich multimedia stuff, especially graphs can be displayed right there, in-line.  It's pretty enabling for scientific computing, enabling very short hacking and visualization cycles almost like a spreadsheet.

I really should write a lot more about this.  It's not just for Python, and it's not just for the web, it seems like it could be a big thing.  It should also make teaching and learning a lot easier.

Check out:

• The IPython Notebook
• How to run code in the IPython Notebook,
• Basic Output
• Rich display system
• matplotlib tutorial

I really like this example, reading a .WAV file and showing side by side plots of amplitude and spectrum:

There are a few things that I think could use improvement.

1. More Document Structure, Real Head 1, 2, 3 and Table of Contents.   I'm a big fan of Mediawiki's nice native built-in structure.  It really helps organize documents in my opinion.  It's also one of the biggest things lacking from Evernote (IMHO).
2. Native Tabular output widgets.  There are some extensions but they aren't quite there yet.  This could make an awesome SQL Workbench, but it could really use ways of presenting and working with tables as output cells.

Enjoy.

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.