In my last post, I described how I ended up finally starting with SDR. I’m experimenting with the Softrock RXTX Ensemble. This kit is a transceiver with 1 Watt output, definitely QRP. It features a USB interface which allows setting the frequency and keying the radio for SSB and PSK31 transmissions. It also has a key jack for CW, and connectors for everything, so you don’t have to hang wires from the board for connections.
Here are some links related to the board:
A word of warning – These kits sell out very fast, and apparently Tony is having trouble getting components. One of the effects of the global recession we’re in is that there are shortages of electronic components, so I’m not sure what the availability will be.
The kit has surface mount components, and requires winding transformers and inductors on small toroids. If you’re not comfortable with this then try to find someone to help you with these parts. Mounting Surface Mount Devices (SMDs) without any special tools other than a very fine-pointed soldering iron and a good head magnifier is not that hard, but it really helps to get some pointers and watch someone else do it. If your vision and motor skills are average or better, then you can do it, and it will be a rewarding project.
The kit can be built for a number of “super bands” as described here. The kit comes with all components for all options, which means that 1) you have to pay attention to the instructions while you build it, and 2) you will have parts left over.
I built mine for the 20m/30m/40m option. This is because I’ll be traveling with it, and having both 20m and 40m gives me bands which are open during day and night, respectively (at least as it stands now in the current solar cycle). I also like 30m, so this is a good set of bands for me.
I built it in exactly the order recommended in the build notes, but didn’t actually test it until it was finished. This isn’t recommended, as the various tests in the build notes are helpful in isolating problems before they get compounded. So this is a case of “do as I say, not as I do”, unless you are confident that you can troubleshoot your way out of problems of your own making. I did have one short caused by sloppy lead clipping, which didn’t cause any damage.
The thing that caused me the most troubleshooting time is that the audio signal coming out of the board is labeled “Line In”, and the signal into the board is labeled “Line Out”. Presumably this labeling is for what they should connect to on your computer sound card but I missed that, despite the fact that it is correctly marked on the schematic and block diagrams.
An aside: The kit includes parts and instructions for a low-pass filter which must be used on the TX output “if transmitting on 30m”. Does anyone know why this would only apply to 30m? Are there stricter requirements for harmonic emissions on 30m? I’ve been meaning to look this up but while I’m writing this maybe I can crowd-source the answer.
One reason I skipped the build tests is that I hadn’t found a good application for Linux that would allow me to control the oscillator on the board using the USB port. There is a ton of information on the softrock yahoo group, in files and in the message archive, but the majority of what’s there relates to using windows applications. I did actually try to use a windows 7 machine to connect to the board, but after losing about 4 hours to erratic behavior caused by conflicts in USB drivers and the application, I gave up. It was a reminder of all the things that I don’t like about windows.
I’m an Ubuntu Linux user (and developer), so I decided to just figure out how to make this all work there, and document it. Everything documented here is for the Ubuntu Lucid 10.04 release.
The one thing you need early in the build is a way to control the oscillator on the board via the USB port. This lets to make sure that it works, and check the quadrature signals to the mixers. On the softrock yahoo group, I found an application named usbsoftrock, which does this. In writing this post, I’ve discovered that usbsoftrock has been packaged for Ubuntu and is available in a PPA by Jonathan, AF6YF (now N6JU). He has some notes here. I’ve not tried this, but hopefully it will work for you and save you the trouble of building it.
Usbsoftrock expects the softrock (USB) device to appear as /dev/softrock. In order to make this happen, you are going to have to add a udev rule. I found a rules file by G3VBV somewhere in my searching of the web. I’m sorry I can’t link to the original because I can’t find it, but I’ve put a copy here. copy that file to /etc/udev/rules.d/88-softrock.rules. You’ll have to be super-user. Make sure it’s owned by root and has permissions 644:
$ sudo chown root:root /etc/udev/rules.d/88-softrock.rules
$ sudo chmod 644 /etc/udev/rules.d/88-softrock.rules
Now restart udev to pick up the new rule:
$ sudo service udev restart
Now, read the 88-softrock.rules file and follow the instructions for adding a softrock group and adding your username to it. Now when you plug in the softrock board, the device /dev/softrock should be automatically created, and you should be able to access it.
Usbsoftrock has an interactive mode that lets you change the frequency through a curses text interface, which is helpful for testing. To invoke it use “usbsoftrock -a interactive”.
That should be enough software to get you through the build.
Next, how I was able to actually receive signals using the softrock and Linux software.