DRM – Digital Radio Mondiale

logo1If you are a computer geek like me, the first thing you will think about when I tell you “DRM” is “Digital Rights Management”. You know, this process that consists in giving you both encrypted content and the keys to decrypt it, but in a really obfuscated way to attempt to discourage you from doing the decryption yourself… anyway, this is not the subject of this post. The DRM I want to talk about today is “Digital Radio Mondiale”. A strange acronym choice if you ask me, but there you go…

Mini game of life

Two months or so ago, the kids and I bought a few bits and pieces at www.adafruit.com to build small LED badges. They had been staying in their box since then, but I eventually got to it with my youngest this Sunday afternoon.

Animated GIF!

Animated GIF!

The idea was to create simple animated badges using the cute 8×8 “mini” LED matrix displays that Adafruit sells, and using some of their small ATTiny45 boards to run the ARV Arduino sketch they described at http://learn.adafruit.com/trinket-slash-gemma-space-invader-pendant/overview .

FriedCircuits USB tester and backpack reloaded

This is a test and review of the new version of the FriedCircuits USB tester and backpack. If you read my previous articles on the backpack and its extensions, you already know that I am a big fan of this simple and very useful tool.

Before going further, one quick word in the interest of full disclosure: William kindly sent me the prototype for this backpack, and I actively contributed to influencing (in a good way I hope) the design of this new version.

So what is new ?

This review is actually about two separate items:

  • The FriedCircuits USB tester breakout v2.0
  • The FriedCircuits OLED backpack v2.0

Both have been improved in this new release, both on the firmware and the hardware sides, so let’s dive a bit deeper…

Sark 110 review

One of the really useful tools you can have as a Ham is an antenna analyser, which enables you to understand better how your antennas and overall RF installation are behaving/performing at various frequencies.

Sark-110 to KX3 Size comparison

Sark-110 to KX3 Size comparison

At the very least, an antenna analyser will let you check the standing wave ratio which, in a very simplified view, is the amount of energy that is being reflected back into your transmitter and not being sent out. A high SWR usually is not a very good thing, though a low SWR does not always mean you have a perfect antenna either, that would be too easy – a 50 Ohm resistor connected to your amplifier will always give you a 1:1 SWR but won’t help you much if you want to make contacts!

Still, understanding how your antenna behaves depending on the frequency, see exactly where it resonates, and how its impedance evolves, is extremely useful. There are many types of antenna analysers on the market, from really cheap kits, to totally awesome tools like the Agilent Fieldfox, or even more advanced stuff that costs as much as a small house… I found a good article at rigexperts which explains a lot of different possible architectures, a good read.

With this in mind, I recently purchased a Sark 110 from Seeed Studio, who sells it for $360 as of January 2014: this antenna analyser is designed for HF to low VHF bands, with a 0 to 230MHz range. This makes it perfect for hams, though being able to include the 70cm band would have been a nice touch. The Sark 110 is fairly priced, especially for what it does: you get much more than a VSWR indicator here!

Quick test of the Matchbox antenna

This afternoon, I did a quick test of the “matchbox” end fed antenna from the Honolulu Emergency Amateur Radio Club, up on a hill,  good receptions reports using only 5 to 7 watts, as you can see below – the sun was setting and the band was closing. As a caveat, I am not doing any sort of absolute judgement on this antenna’s performance, just a bit of field test feedback!

Reception reports matchbox antenna

Reception reports matchbox antenna on 20m

Digital signals on the waterfall

Collection of various digital modes – images for now, maybe audio later. The idea here is to take waterfall screenshots in ‘real life’ environments, on a noisy waterfall, to serve as a reference on the software I use most often, fldigi.

These are all signals I received on my KX3, unless stated otherwise, and which I successfully decoded. This is a work in progress, I will add additional modes as I go along, so check back every once in a while! If there are modes you would like me to look for, let me know.

Meta digital

A fairly common practice is to use preambles to tell digital software what mode is going to be transmitted. There are mainly two types of preambles: “Reed Solomon ID” and video preamble. A good example of video preamble on a noisy waterfall can be found below:

Video ID then RSID before an Olivia transmission

Video ID then RSID before an Olivia transmission

More info on RSID can be found here: http://www.w1hkj.com/RSID_description.html

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!