State of SDR on *Nix

sdrheadergraphic1

After building, and running the SDR radio, I can reflect a little on the state of SDR on Unix/Linux operating systems. It’s not a crowded space. A few others have gone down this path, including kb8ojh at http://www.kb8ojh.net. He has a few suggestions about SDR software. He enumerates the short list: Linrad, DttSP+SDR-Shell, GNU Radio, and Quisk. Quisk is an all-python program (yes, even the demod) – and it runs fine on Linux. On FreeBSD, there seems to be an issue either with the port or with my setup (yet to be determined). GNU Radio is nice, but kind of a monster to build and install. I’m much more into the simple plan, and that’s why I finally just decided to use venerable old Linrad. Its package is absolutely tiny compared to GNU Radio.

There is also the OSMO SDR project, the RTL-SDR project, and the GQRX project. While these projects are all targeted to the USB RTL dongles (or similar) and their USB audio, it is said that they can be configured to work with standard sound cards. It’s on my TODO list to check that out. For a complete interface though – I think those packages make use of the GNU Radio package again, and its city block sized infrastructure.

Linrad’s old X style interface makes it stand-offish at the beginning, but the text mode line-by-line configuration is better than having to figure out what to put in the configuration files by yourself (many *nix world programs)! After using it for awhile with the soft66, I can say that I’ve internalized the older interface such that it doesn’t bother me at all. I like its simplicity. It’s configurable to the point of a test lab instrument, IMO. It seems like it should be a good candidate for an upgrade to GTK3, but I think the developer is more keenly connected to the back-end details (what really matters).

Windows is where you will find all the glitzy SDR software. Some of the screenshots look downright tantalizing, but I don’t run Windows. At one time, amateurs were testing the waters with Linux, but I think many who did have fallen back to Windows for most of their work. A number of ham related ports have gone years without an update. SDR has been around for a while (Linrad dates to 2000, but is actively maintained). SDR radio is now catching on in the realm of commercial ham gear (Flex, etc) and the wildly popular webSDR project. To run a webSDR site requires hardware, and a number of firms now provide SDR hardware that can be used for the purpose (CrossCountry’s SDR comes to mind). In fact, not a small number of webSDR sites are using the soft66 hardware! Since it’s so inexpensive, some operators have put gangs of five or six of them to use inside their webSDR setups, each tuned to a different band. They often use various additional amps and filters in their setups, from what I’m reading, so the cost must be a little more.

shortdeplistlinrad1 Figure 3: The short dependency list of linrad is nice and simple. Guess there’s a benefit to the old X interface!

Technically, there are other dependencies if you're using an rtl dongle, control software or port-audio:

LIB_DEPENDS=    librtlsdr.so:${PORTSDIR}/comms/rtl-sdr \
                libportaudio.so:${PORTSDIR}/audio/portaudio \
                libftdi.so:${PORTSDIR}/devel/libftdi
                libsoft66

That brings up the question “Why don’t I use the dongles?” (since they’re cheap). The reason is that a real radio has parts, and specifically, parts that are quite well tuned to the task at hand (HF ham/shortwave band reception, in this case). With a few exceptions, dongles must have down converters to HF (their low end is usually VHF) and that means HF level hardware must be added anyway, and I’d have more cost in the unit than I do now.

crystals Here are the five crystals included with soft66. The two small ones are for six meters.

The website for the SDR board I’m using does not really specify the number of crystals included in the kit, so that may be variable (don’t know).

It may be necessary to add some more hardware to this setup to make it bang-up spiffy, but at $20 (with shipping included) there’s no excuse for anybody to “not have tried” the SDR way of things. Go for it! Note that I don’t have any connection with Soft66 or its maker, so the cost may vary from what I paid.

Note: Linrad and Quisk are projects maintained by other people, and have no association with this site. Information can be found about those projects via google.

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