Sunday, December 28, 2014

Amateur Radio information on modern social networking.

I'm slowly starting to get some of the appeal of Reddit.    At first I was drawn there by /r/rtlsdr, as there didn't seem to be much info elsewhere.   There is a bit of a digital divide, for on-line sources many hams go to with it's 1990's design and god awful ads flashing all over the page.  Try as you might, some of the old guys can't remember to try anything but The other big source of info is Yahoo groups which are starting to show their age, but have been made much less useful due to Yahoo trying to figure out how to get more page views.

So two useful places to get answers to amateur radio related info:
  1. Reddit: /r/amateurradio  []
  2. StackExchange: []

Wednesday, December 17, 2014

Decoding 433.92 Mhz devices with RTL_433.

I've been doing a bit of playing with merbanan's rtl_433, which uses the rtl_sdr code to decode signals from 433 Mhz ISM devices that mostly use On-Off-Keying.

So far I've been working on decoding
  • Lacrosse TX-7 temperature and humidity sensors, same protocol as TX-3, TX-6.
  • DSC wireless security contacts (door/windows, smoke and carbon monoxide detectors)
There is a lot I've learned from playing with the devices using rtl_433 and digging into the code.  I need to write it up because there are almost no instructions.

I've posted the LaCrosse code to github and submitted a pull request to merbanan/rtl_433.

I'm successfully decoding the DSC contacts using a separate Python script that parses the debug output from rtl_433.  I need to write a new pulse decoder for rtl_433 in order to handle the DSC protocol as it's a little different than other pulse or distance coded signals. It doesn't send anything for a zero (0) bit, so there can be long periods (up to 8 bit slots) of no signal.

For more info, contact me if I haven't posted here or to github.

Update: 2015-01-11, merbanan processed a whole bunch of pull requests, including mine, so the LaCrosse TX-7 support is now in the main merbanan/rtl_433 github repository.

I haven't pushed any code for the DSC sensors yet. I have to decide how I want to do the decoder and call back yet.  Anything I push will probably be only be in rct/rtl_433 for a while as it is likely to be experimental.

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

Saturday, November 22, 2014

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)

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 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.

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 .

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.)

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,

Trying to get active again

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

Let me try to fix that.

Thursday, May 1, 2014

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.

Tuesday, April 29, 2014

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 knowledge base
The solution is to use mke2fs ... -I 128 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.

Saturday, March 29, 2014

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:
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.

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:

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.

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

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.



Wednesday, February 26, 2014

Vodafone mobile network in a back pack - "Go Kits" for restoring communications

From Engadget - Vodafone's network in a backpack connects people after natural disasters:

This story has a couple of interesting points to Amateur Radio people who have been building go kits to provide communications when there is no infrastructure for several decages now.

This mobile phone carrier has two types of Go kits (one 220 lbs, and now a 24 lb backpack) that they can deploy to disaster areas to provide communications services.

The backpack has "2G GSM connection capable of handling thousands of text messages and five calls made at once to people within a 328-foot radius. It's equipped with a GSM base transceiver that uses satellite connection to link up to a host network."

(Note: Thousands of text messages vs. 5 simultaneous voice calls.  So it's important to educate people that text messaging has a much better chance of getting through during times of network issues whether it's congestion or outages.  People will eventually figure this out, but may loose valuable time and/or battery power.)

Details on larger version:  "In fact, during Vodafone's mission to the Philippines following Typhoon Haiyan, two 220-pound kits handled a total of 1.4 million text messages and 443,288 calls within 29 days. Obviously, the larger machine has a wider operating radius (3 miles), but the Mini has its own set of pros. Since it can be deployed within minutes and be carried on planes, it can potentially help more people -- and more quickly, too."

This implies that the 220 lb kit can't be carried on a plane, which sounds like a serious limiting factor for deployment. Possibly it's just due to the reporting in the story. 220 lbs is not a problem weight wise. So perhaps actual size, batteries, or the inclusion of generator keeps it from going on planes.

Tuesday, February 18, 2014

"encyclopedia" of digital modes (modulation/encoding)

This looks like it could be very useful for those interested in decoding or understanding various digital modes, how they are encoded/modulated.

The web site is:

There are print books for sale for HF modes and another for VHF/UHF. Roland Proesch is the author. (The books are available in german and english)

For each book a PDF except is available for free that still has lots of helpful information in it.

In addition to a brief description for each signal are a number of pictures of oscilloscope and sonogram/waterfall type views.

RTL-SDR users would find the VHF/UHF book directly relevant. However the HF book looks like it might provide a better foundation.

Take a look at
  • HF: (81 pages) -
  • VHF/UHF: (56 pages) -
Unfortunately, it doesn't look like he's selling the complete books in electronic form, only print. I came across this from a post to the digitalradio yahoo group by Ian Wade, G3NRW.

I've also forwarded this to which I find is a very useful blog for SDR and digital modes.

Thursday, January 2, 2014

AUXFOG: Auxiliary Communications Field Operations Guide. (Free PDF)

FYI - Here's a free, handy reference guide to have around.  It's a version of the DHS "National Interoperability Field Operations Guide" (NIFOG) that has been adapted to be more appropriate for our uses.  It contains frequency information for many other radio services that you might want to have programmed in a scanner or radio with some available memories.  There is also some tutorial information including some antennas that can be easily constructed.

"The Auxiliary Communications Field Operations Guide (AUXFOG) is a reference for auxiliary communicators who directly support backup emergency communications for State/local public safety entities or for an amateur radio organization supporting public safety.

This reference guide contains information about AuxComm best practices, frequently used radio frequencies, Mutual Aid channels as well as tips and suggestions about auxiliary emergency communicators integrating into a NIMS ICS environment to support communications for planned events or incidents. It can serve as a reference both for auxiliary emergency communicators and public safety communications professionals. You can download the AUXFOG by clicking on the hyperlink to the left and save it to your own storage device. It will only download as a PDF.

While printed copies are not available from DHS, you may download an electronic copy to print as many hard copies as desired."

Trying Linux and amateur radio software without having to install it on your computer.

The topic of trying Linux without having to actually install it on your computer came up recently.   There are several "Live" distributions which can be downloaded to a bootable DVD or USB thumb drive. You can then boot your computer from the DVD or USB drive without having to touch the existing installation on your hard drive.

The simplest approach is to download the DVD .iso, burn it to a blank DVD, and then reboot your computer, telling it to boot from the DVD drive.

The USB thumb drive approach has more steps to create, but can be faster as well as allowing you to save changes between reboots.

Two ham radio oriented builds that have been mentioned:

Both are based on Ubuntu Linux and include software such as FLdigi and Chirp.

If you are interested in trying them, I think there are better tutorials available if you google "ubuntu live" than the instructions that accompany the two ham specific packages mentioned above.

Rigol DS1052E/DS1102 and Linux, Python, usbtmc

[To Be Updated]
This is one of those intersections of electronics, open source, hacking, and programming that really gets my interest.

Here are some links with information on connecting the Rigol scope to Linux, and controlling it using Python via USB.  The scope implements the USB test and measurement class, usbtmc.