Tetra decoding on a stationary PC or a laptop is good for experiments, but not really suitable for replacing the classical scanner – a standalone device that’s always can be on, independently on what other you want to do on the PC’s
It’s though actually quite cheap and easy to create a Tetra-scanner. Thanks the SQ5BPF’s software, a suitable linux distribution and something called NUC from Intel, you can build your own Tetra scanner for less than 250 USD and be up and running in 3 hours.
The Intel NUC is a very small PC, similar to a portable HD, which is very suitable for running Linux and some Tetra decoding. Due to the size and ability to work without any monitor, it's perfect to send away to some friend at an interesting radio-location.
The 250 USD variant is suitable for decoding 2 channels systems, but if you double the price you can now without any problem decode at least a 6 channel system, or three 2 channel systems at the same time if you so like.
If you check my old reports you can found that I've before have tested three different Intel NUC PC's of last year model. Now it’s a new year, and I’ve started by testing the mid-range NUC from the 2015-series: Intel NUC 5i5RYH.
Mini PC Intel® NUC Kit NUC5i5RYH
In the 2015-series of NUC's Intel have released three CPU versions; i3-5010U, i5-5250U and i7-5557U. And since i5-5250U is a direct replacement of 2014’s best model D54250WYKH, I decided to start testing this one. Both are still sold, and the price different is only 30 USD.
With the 2014 best model I could only decode 4 channels at the same time. Using it to decode 6 channels worked, but with very high CPU load, temperature, fan speed and with lost frames and bad sounds, so I was curious to see how well the 2015 equivalent would perform.
And yes, the new model was a lot better. When I monitor a 6 channel system, the CPU total reach 100% (the two physical cores added), but the automatic overclocking is not going to max, so the 100% is not saying so much since the CPU speed will increase if I load it more.
Compared to the 2014 years mode which had an i5-4250U CPU, the 2015 mode has i5-5250U. Both are dual core CPU’s with support for hyperthreading. In my previous tests I notice that the hyperthreading ability is really important when monitoring several tetra frequencies since it’s quite a lot of data in different threads that has to be processed within a short time frame. If I instead run a faster dual core CPU without hyperthreading, the result is quite poor.
The clock speed of the new model, 1,6 GHz compared to 1,3 GHz is of importance. But maybe even more important is that the automatic overclocking in the new model works a lot better (by default). I never really got the overclocking to work well in the NUC from 2014, but in this years model it seem s to work just fine.
It’s though important to mention that the comparison is not fully equal since I’m both running a later linux distribution and gnu-radio version on the new NUC. So maybe it’s the later linux distribution that’s better on handling the overckocking, or the new gnu-radio which is more light to run. So I might have to revise my conclusions if I update my old NUC sometime later.
On the new NUC I’m running Lubuntu 15.04, and this is important. The 2015 NUC’s must have Linux kernel 3.19, else the graphics just become a mess.
Running Lubuntu 15.04 (and probably other Ubuntu variants too) is though not fully compatible with the gnuradio install script. First of all the script doesn’t expect anything higher than 14.*, but it also tries to install libqwt5-qt4-dev which collides with libqwt6 which already is installed in Lubuntu 15.04. So this also has to be modified in the script.
And this is not enough… the gnu-radio installation script available also have a problem that I believe anyone who currently try to install Gnu-Radio 3.7 will run into. The VOLK-component is not checked out as standard, so to the git clone command –recursive has to be added to get a successful installation;
Git clone –progress –recursive h t t p://git.gnuradio.org/git/gnuradio.git
So maybe this explains the problem that some users run into if they don’t notice the error in the gnuradio installation and just continue trying to install the tetra applications.
Anyway, when modifying the script, it’s just to install the remaining Telive-applications by the instruction and everything works like a charm.
With Gnu-radio 3.7 I’ve both tested the RTL-SDR and the AIRSPY. Both works fine together with this Lubuntu-version and NUC, but I could only run ARISPY with 2,5 MHz bandwidth. So maybe the 2015-top-model i7-5557U is required to get the full advantage from the AIRSPY together with Telive. The reception quality is significantly better with the AIRSPY, and no PPM correction is needed. I could actually decode a remote signal which just had 5dB S/N ratio (no audio, but enough signal to get the system parameters after some seconds.
So if anyone before was thinking of buying a NUC to get a permanent Tetra receiver, I can highly recommend the 2015-series. You will have to be prepared to be locked to certain linux distributions due to the kernel limitation, and at the moment you will also need to tweak the installation script to get gnuradio in place. But beside that, you will get a lot more for then money than you had with the last year model.
The only thing that’s become worse since last year is that they have moved the place of the USB and HDMI connectors, so on the 2015-model it’s not possible (without USB-cable) to connect RTL-SDR at the same time as the HDMI on the same site. And I prefer to have all the cables on the same side of the box.
