Wednesday, June 13, 2012

Using an Oscilloscope to Check Your (Transmitted) Signal

N2NOV had posted that Tektronix now has a Youtube channel with videos on how to properly use an Oscilloscope.  Many years ago, Tektronix published a good free PDF, The XYZ's of Oscilloscopes. It was
good but a little dry compared to a video presentation.

Well equipped radio operators have a special type of dedicated oscilloscope called a service monitor which allows viewing your transmitted signal, by tapping the radio frequency (RF) from the transmission line. Recently I came across a Youtube video that showed how to build a very simple RF sampling circuit that would allow using a common oscilloscope to monitor the RF output of your transmitter (transceiver).  While this won't do everything that a dedicated service monitor would do, it's a pretty cool way to check your signal if you only have an oscilloscope.  The RF sampler circuit described should be less than $10 in parts.

Personally I find this sort of thing to be very cool.  Even if I had an unlimited budget for buying equipment. I don't have the room to store it in NYC.

Note: This will only be useful for monitoring AM and SSB transmissions. I hope to come across something not too difficult to build that would be useful for looking at the output of an FM transmitter like the type most commonly used on VHF and UHF.

Good Tutorial on TCP/IP Diagnostics using Traceroute

MTK, just sent me this today.  It's a presentation and paper by Richard A. Steenbergen, from 2009 that covers the finer points of diagnosing TCP/IP networking problems with Traceroute.  It looks like it was originally presented as a tutorial at NANOG.  Why am I posting this?  If you tried to google "traceroute tutorial" you'd get tons of fairly lame overviews that show some traceroute output and attempt to explain it. 

To quote one of the intro slides:
Few people are actually skilled at interpreting traceroute.  Most ISP NOCs and even most mid-level engineering staff are not able to correctly interpret a complex traceroute.  This Leads to a significant number of misdiagnosed issues, false reports, etc, which flood the NOCs of networks world-wide.  The false report rate is so high that it is almost impossible to
report a real traceroute-based issue through all the noise.
There is a lot of nitty gritty practical details in here. Even if you rarely use traceroute, you'll learn a lot from this. This is one of those rare, good presentations and papers to file away so you can refer back to it and hopefully use to enlighten others.
Hope This Helps.

Sunday, June 10, 2012

Hams, Yahoo Groups and private message archives

Someone asked about learning the Yaesu VX-8 on one of the mailing lists I subscribe to. I sent the following response which has got general advice about Yahoo groups which seem to be popular with ham radio people. The most important bit:
If you are a member of any active Yahoo group that has useful information to share, consider lobbying the group's owner to make the message archive public.  It makes the information more accessible and should cut down on some of the redundant questions.
Please spread the word. The more information that is easily searchable the more we all benefit. 

Here's the original response:

I have a Yaesu VX-8DR and would be happy to answer questions about it.It has a lot of features and the manual isn't always as straightforward as it could be. I've learned a lot from reading the VX-8 Yahoo group for the last 2-3 years.

I suggest joining the Yahoo VX-8 Group, and then reading some of the old message traffic.  Many of the questions about the radio have been asked and answered since it came out.  Also check through the files and links section of the yahoo group.  There are some documents people have put together on working satellites, APRS and the ISS, etc.

Yahoo groups seem to be pretty popular for hams and there appears to be one for most popular radios.  If you have, or are considering purchasing a particular radio, check to see if an active yahoo group exists for it.
Then join it and look through the message and file archive.

Unfortunately one drawback of Yahoo groups is by default the message archive is only accessible by  members.  This means Google and the other search engines can't index the information stored in them.  The result is it's harder for you to search for answers to your questions.  You'll need to go to the Yahoo group and use its search function to look for answers.  (I still recommend using google to search for answers that might be available on the open internet in blog posts, open forums, etc.)

If you are a member of any active Yahoo group that has useful information to share, consider lobbying the group's owner to make the message archive public.  It makes the information more accessible and should cut down on some of the redundant questions.

Here are a few groups that I belong to that I'd like to get opened up:
There's a lot of knowledge locked up in those groups.

Hope This Helps,

Tuesday, April 24, 2012

APRSDroid, freely available APRS app for Android phones

Here's another post that I've sent to a mailing list, that I thought might be worth sharing more widely. Many more people have Android phones with a built in GPS than have APRS capabilities via their radios.  This could be a useful tool in the toolbox for those who do public service events.

The APRSdroid application provides APRS functionality for Android Phones. An installable .apk as well as the source code are freely available from the developer's site.
The same application is also available in the Android Market for $4.50, which is an option for supporting the developer.

The app enables sending and receiving APRS beacons and messages via a data (internet) connection to the APRS-IS network.  Map data is also downloaded from the internet.  (This mode requires that you have cellular data coverage.)

The app can also generate AFSK tones for sending ARPS beacons and messages via a connection from your phone's earphone jack to your HT's microphone. Note VOX capability is needed.  The ability to decode AFSK tones isn't implemented yet, so it's not a complete software TNC replacement. However, it's on the requested feature list.

I was successful in making a straight-through connection from my Samsung Galaxy Nexus to my Wouxun KG-UV2D.  My Yaesu VX-8DR had no problems decoding the packets from APRSdroid via the Wouxun.   I need to go out to some open spaces to test how well it will be picked up by actual APRS digitpeaters.  It can be pretty hard to get APRS beacons out on NYC streets.   In general 2 meters can be pretty spotty on the streets in NYC. 70cm does a much better job of being reflected off of buildings, which is expected.

An alternate version of the application that uses pre-downloaded offline maps is available. This can be handy in places where there is no cellular coverage. I was able to get APRSdroid loaded and running on the Kindle Fire using the offline maps version (OSM).  The Kindle Fire is really too limited of a device to be useful for APRS since it doesn't have GPS or cellular data service.  However, it does have a 7" screen which would be useful for

iPhone users: I've seen similar apps listed in the app store, but I have no experience with them.

Tuesday, April 17, 2012

Amateur Radio License Free On-line Resources

During an on-air net, someone asked for on-line help in preparing for the Amateur Radio General Class license.  I sent this response to the group mailing list:

Free Study Guides

These are dense summaries of all of the material covered by the current question pools. For some topics the study guide treatment is enough.  For other topics, reading a full guide like the ARRL License Manuals is recommended. If you have enough time, I recommend reading the ARRL license manuals cover to cover, you'll learn quite a bit and they are a fairly light read.  The study guides still help because the license manuals can be quite verbose and even rambling at times.  Having a nice dense summary helps to crystallize what you need to know.

Note: There are quite a few study guides and slide presentations available on-line. The ones I listed above are the ones that I've seen and read. Many groups pull together similar material when then offer a Ham Cram class.  Some groups have a single day session where they attempt to cover all the material for you to take your test the same day.;

Check the Dates on Study Materials!

The question pools used for exams change every four years.  Additionally the rules governing amateur radio do periodically change which affects the answers to some of the questions. Make sure any study materials you are using are covering the test pool that will be used at the time you take your test!  While Amazon is a generally one of the easiest places to buy books, it's fairly difficult to tell if you are getting the correct current edition.

Practice tests and On-line Flash Cards

There are a number of web sites that will let you take a practice test.  Some sites offer all the questions in the test pool as "flash cards" so you can try every question.  There are many of these sites out there.  Many of them are very basic or feature poor.  The one that I found the best when I was studying was It's well implemented and keeps track of what questions you've seen and answered correctly.  If you practice with it for long enough you will cover the entire question pool. The statistics will let you know which sections of the test you are struggling with.

ARRL License Manual Supplemental Material

There are some additional resources on the web site that aren't well publicized.  For example, in the back of the license manual books is a full copy of the question pool. However the book doesn't present the material in the same order as the question pool. When reading the book and trying to test yourself on the question pool, you have to skip around a lot.  A version of the question pool that is in the same order as the material as the book is available. I think this should have been the version printed in the book.
Supplemental Material:

Multiple Choice Test Strategies

It's worth reviewing tips for taking multiple-choice tests. Namely for most questions two of the choices can usually be quickly eliminated as wrong answers. Doing so leaves you with two possible answers, giving you at 50% chance of getting it right even if you have to make a guess between the remaining answers.

Hope This Helps,

Wednesday, April 11, 2012

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.

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

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:
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.
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.
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.
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."
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.

Monday, April 9, 2012

Interfacing Radios to computer sound cards.

A question that frequently comes up on some of the various radio mailing lists I'm on is how to interface the radio to a computer for doing digital modes via the sound card. The sound card provides the equivalent of a modem, doing digital to analog and analog to digital conversion.

Skip Tellar, KH6TY, has a design called DigiVOX that was in the March 2011 QST for sound card interfacing. It will do a VOX function for activating the Push-To-Talk for doing digital modes without using any additional signaling lines.

Mark Phillips, NI2O, sells a kit called USB Digivox that combines a USB sound
card and KH6TY's digiVOX interface at his Go Box Gizmos site. This simplifies the setup and gives a dedicated sound card for the radio analog to digital and vice-versa.

Argent Data systems is a good source for a microphone/speaker cable for connecting to Kenwood, Wouxun, Puxing, and other chinese radios that emulate the Kenwood.

The software that is the most popular for doing sound card digital modes is FLdigi by W1HKJ. It can do quite a few different modes and is cross platform. It's got a lot of functionality and though has a bit of a learning curve. Fortunately there are a lot of tutorials out there on how to use FLdigi.

Note: Laptops often have a MIC input connector and not a line level input. On the ring of the MIC connector is 2-5V for biasing the microphone element. You want to take care with this, I'd at least make sure to put a capacitor to block the DC or make no connection to that side. If I remember correctly it corresponds to the Right (Red) channel.

13 months since my last post!

Oh, now I'm a bit ashamed that I haven't posted anything to this blog since February 2011. I thought I would have at least posted semi-annually.

I'm going to try to post some of the more helpful answers that I send to various discussion groups in the hopes that more people will be able to find my answers and get more value out of them. Also it might help me find stuff I've posted before so I don't keep rewriting it.

Some of these "answers" might seem a bit out of context. Sorry about that. I don't really anticipate that anyone is really reading this blog sequentially. All I can hope for is that someone might find one of my entries through some googling.

On-line code of conduct for corporate citizens.

I stumbled across UpMan's Rules of Conduct which seemed like a great set of guidelines to follow, not just if you are working for corporate entity and posting on-line.