Cheap sound cards – and what do do about them

June 2014 Update: Macports really supports GNURadio very well these days, so you can install the iq-imbalance package directly from it now: port install gr-iqimbalance . Another approach is to skip this entirely and resynchronize the sample shift from the sound card, see the article for more details.

A quick example of what a bad sound card does when used as an SDR I/Q input: the waterfall below is very symptomatic. I used a cheap USB sound card bought for a few bucks on Amazon. It works perfectly for digital modes, since those do not use the stereo signal, but with the IQ output using both left & right, here is the result:

Sound card with left/right phase issues

Sound card with left/right phase issues

KX3 Gnuradio spectrum visualisations

Using the IQ output of the Elecraft KX3 is a lot of fun when combined with GNURadio and the Gnuradio companion. This article is a very quick introduction to GNURadio and how you can use the various out of the box visualisations in literally 5 minutes, including the fancy ‘fosphor‘ spectrum analyser!

As I mentioned before, installing GNURadio on the Mac is now a breeze, thanks to Macports (sudo port install gnuradio +full). You can add the fosphor block the same way: “sudo port install gr-fosphor”. Then you just need to fire up the GNURadio Companion app and build a very simple flow graph, as shown below:

1000 Miles per Watt!

After getting my HAM license in November 2013, I decided to buy an Elecraft KX3¬†as my first radio – I will have to post more info on that rig one of these days, it is fairly impressive. Elecraft enjoys what can only be described as a cult following, thanks to both making awesome hardware, and having one of the best customer support in the industry. Anyway…

One of the important properties of the KX3, is that it is a low power radio, with a maximum power output of about 10 Watts. In the Amateur Radio world, this is what is known as a “QRP” or “low power” rig: QPR is a complete sub-scene of the HAM hobby, dedicated to making contacts as remote as possible, using as little power as possible.

HAM Operation on a Mac

Here are my notes on setting up a software suite to manage an Amateur radio station, using MacOS. Traditionally, Windows has been the platform of reference for most HAM software, followed closely by Linux, and us Mac users kind of got the short end of the stick until now.

At the end of the day, though, a lot of Linux ham software actually works well on the Mac, and there are really good programs for this platform too, this article describes how my own station is setup today.

RUMLog, fldigi and gr-kx3

This first article covers the basics: rig control, digital mode software, and logging. A second part will describe more advanced settings, such as audio monitoring using audio multiplexers on the Mac.

I am still a very new HAM operator, so if you have additional hints to offer, or would like me to go deeper on some aspects, please contact me, I will gladly improve this article!

HAM license

KX3_small1Amateur Radio! Or “HAM Radio” in English. A subject that has been a source of fascination for me since I was a kid, but has remained very closed as long as I lived in France.

All my attempts to get licensed over there were met with frowns and grunts by people who were all about telling me that amateur radio was a very serious thing and that I did not have a clue what it was really about etc… In short, not very welcoming! I still remember my last attempt in Paris to learn more about the hobby in a local club, which resulted in a “yeah, you want to become a HAM, right… you know, it’s not Internet, you will probably not be interested once you realise what it is, young man, get yourself a pair of walkie talkies and have fun…” , after which I decided to call it a day.

Fast forward about two years: I moved to California, and was invited to the Bay Area Maker Faire in 2013 to show off some of my work. While I was there, I had the opportunity to meet members of a local amateur radio association: it was a “day vs. night” sort of experience. Open, friendly people, passionate about their hobby and who enthusiastically encouraged me to study for my license and join their ranks! So I spent some time to learn about regulations and refresh a bit on radio fundamentals, and finally took my Technician and General FCC licenses at the end of November 2013. Again, cool and friendly people at the exam, all good.

So stay tuned for new kinds of articles on this blog, as I get deeper into this new world!

73 de W6ELA