It's not my first software radio platform (I've already enjoyed for about couple of years experimenting with bladeRF), but FDM-DUO has the big advantage of integrating the digital and analog circuitry with sleek, minimalistic, knobbed user interface in a small, handy package. The radio can be used as an SDR interface to an application running on a computer, but can also be used as a traditional, standalone HF transceiver.
Using the radio as a standalone TRX is pretty straightforward. Connect the antenna, microphone, power cord, and you're ready to get on the air; However, I did not spend over one grand on a digital radio just to play with knobs. It's an SDR after all!
Since a long time ago I found Windows useless for all my daily tasks, I had no platform on which I could run the application. One option was to use Windows VM, but experiments with VirtualBox and pre-recorded RF captures provided by Elad showed very poor performance of such setup.
Since I have no use for a full-blown Windows PC, I decided to buy a small, cheap tablet which can be easily turned into an SDR appliance and tucked away when not in use. Following the advice from Elad mailing list, I decided to buy TW100, a 10.1" tablet made by WinBook. Nearby Microcenter had good deals on open-box tablets, so an hour and $104+tax later I brought home a small, lightweight Windows PC. I did not have enough time to test the setup well, so I will not do a full review of neither the tablet nor the software, but I'd like to share my impressions after one evening of playing with them.
The tabletAt this price I did not have very high expectations from the device. It's cheap, works, can run FDM-SW2, and does not take much space on the desk. That's all I needed.
- It's cheap. At this price I can afford experimentation.
- Has mini-USB and full-size USB3 connector.
- Can be charged through mini-USB, while USB3 connector is used for external devices.
- Runs Windows 8.1, what lets me use it with Elad's software.
- Has processor powerful enough to run FDM-SW2. Initial tests with single instance of receiver at 768kSps showed less than 25% of CPU usage, what is more than enough for HAM use.
- Big, well readable 10.1" screen.
- Tablet came with no bloatware, or unnecessary applications.
- It's cheap. Thick, clunky, feels low quality.
- Runs Windows 8.1. I don't know how intoxicated one had to be to imagine that a desktop OS could be used on tablets. The tablet-ish "Start" screen is not enough to make the UI touch-friendly.
- Low resolution screen. 1280x800 pixels screen is barely enough to fit the main application window. It's too small to show the SW2 application window and one receiver window without having to switch between them.
FDM-SW2After connecting the tablet to power supply, and short, 4-hour long installation of all urgent updates from Microsoft, the tablet was ready for installation of Elad's application. The installer downloaded and installed all third-party libraries, and in a short time SW2 was ready to use. With DUO connected to the tablet, the application immediately showed the main window, without asking whether to start in offline mode, or connect to a server. It took me a while to figure out how to start processing, but after a few minutes of pressing random buttons, I managed to start it.
- Up to 4 independent demodulators working in parallel.
- The DSP algorithms are quite efficient. With streaming at 768kSps and two SSB demodulators active, CPU usage was below 25%. It was only few percent higher than with streaming at 192kSps.
- Extensive capabilities. Lots of options are available, lots of parameters can be changed. Maybe even too many (see cons below).
- Can be used as a DSP application and FDM DUO manager.
- User interface is confusing. I really like the user interface on my DUO. It's simple, logical, and easy to use. Unfortunately I can't tell the same about SW2. The software is very powerful and the UI designer wanted to make most of the options readily available, but in my opinion it went a step or two too far. As a result we've got an overloaded UI, with non-descriptive (sometimes even confusing) markings, barely fitting in the window. It does not mean that it's difficult to use; Once I figured out what the cryptic names on buttons mean, using the software was not a problem, but the first impression was very WTF-ish and made me miss simple and minimalistic UI of GQRX. Adding descriptive tool tips would be very helpful; However, what the application really needs is full UI redesign.
- Complex UI is not touch-friendly. It's not really Elad's fault, but it's something to consider for anyone who wants to use it on a tablet. With so many tiny controls it's impossible to accurately aim in the right spot (fat-fingers problem). Just remember to have mouse handy.
- Bloated GUI. I don't remember when was the last time I had a chance to watch an application redrawing its interface. Must have been like 20 years ago, when I was using underpowered SUN IPX workstations. Late 1990-ish X11 on Linux without graphics acceleration was fast enough to make widget rendering almost instant. And yesterday I had to rewind my memories.
I realize that the GPU in the tablet is not very powerful, but it's strong enough to make OS and other applications rendering smoothly. But not for SW2. Every time a window opens, it takes about half a second to draw its elements, during which I can watch as it draws the buttons. With such heavy GUI I'm not surprised that VirtualBox, with its non-accelerated graphics driver had problems with processing: refreshing the GUI elements was eating so much CPU time, that not much was left for DSP routines.
- 1280x800px is not enough to have the main app and demodulator windows open. As I mentioned earlier, the screen does not have enough pixels to use SW2 comfortably. Even with main windows width reduced to minimum, it still overlaps the other windows.
ConclusionsI did not expect much from the tablet. For the price I paid it's a very good buy. However, because of the screen estate I consider returning it to the store. I wouldn't mind 7" or 8" screen, but with higher resolution. The only reason why I have not done it yet is the separate charging connector. If I can find a reasonably-priced PC tablet with separate charge socket, I will take TW100 back to the store.
Update 2015-06-11: I no longer get excited by the view frequency spectrum, or the fact that I can listen to several signals concurrently. I need to computer which I can use for something useful, not just to toy with SDR.
Tablet went back to the store.
Update 2015-06-21: I've got a TW802. Has most of the limitations of TW100, but at least it's lighter, smaller, and much more handy. I still won't be able to use the main window and demod windows at the same time, but at least I can use the tablet as a panadapter, which is useful.
Update 2016-02-20: Since Elad released GnuRadio block and programming example for DUO, I can no longer claim that the company has no plans for Linux support. No words can tell how happy I am about it.