SDRangel recently had an update (v7.8.1) with a couple of enhancements and fixes. One of the updates was an addition of adding a dial to flip through DATV standard symbol rates. It’s not a big change, but it has inspired me to download it and try to decode some DATV transmissions from QO-100. Being a newbie to SDRangel it took me a while to get it going. The interface is a bit different and if you don’t know it well then it can be tricky to find the options needed. This article outlines a few simple steps to get going on demodulating and decoding a DATV signal.
The install process is fairly simple, but keep in mind I have only tried this on Windows. Download the latest release from here. As of 2022/10/27 it is the sdrangel-7.8.1-win64.exe file. Simply run the installer and go through the steps. Nothing funny here.
Once it is installed you will find the SDRangel shortcut in your start menu.
Note: I’m assuming that you have the hardware all setup and ready. If you need more information then check out the handy guide on the BATC Wiki on aligning your dish. You will at the least need a dish (preferably 1m or larger), a LNB, a Bias T for powering the LNB and a SDR.
At this point you can plug in your SDR and start SDRangel. Depending on which SDR you use you might need to install some additional drivers first, but it has native support for most SDR devices. For more information on your specific SDR check out the SDRangel RX Devices Documentation.
First step is to click on the RX Device icon and you should be presented with a list of available RX devices on your computer. I’m using the Airspy SDR.
Once your SDR has been selected you should be presented with the following two windows:
To connect and start your sdr, click on the blue play button.
To change the frequency hover your mouse over the current frequency and use your scroll wheel to adjust up and down.
With my current QO-100 hardware, I can find the Wideband beacon around 741 MHz. If your hardware is correctly setup then you should be able to see the beacon on the waterfall and possibly a few other DATV signals. Keep in mind that depending on which SDR you are using you might see less of the wideband spectrum due to your SDR having less bandwidth.
If you have reached this point then we can attempt to demodulate a DATV signal. If you don’t see at least the beacon then something might be wrong with your setup and its time to retrace your steps.
The next step is to add the DATV Demodulator plugin. To do that click on the Add Channels button and select DATV Demodulator.
Lets start by trying to demodulate the QO-100 DATV beacon and also display it. First we need to set the following settings.
Signals on QO-100 should normally be DVB-S2 and QPSK, although you will find the the odd 8PSK signal. You should also set your Symbol Rate. The beacon is running at 1500000 sym/s. You need to enable SOFT LDPC and we also want to see a video feed so also enable the Video checkbox.
Next step is to tune to the beacon signal. You can click on the waterfall, try to tune to the center of the signal and make sure the bandwidth is covering the entire signal:
You can adjust the bandwidth on the DATV Demodulator screen as needed. This will vary depending on whether you are tuning onto a 1500m/s signal like the beacon, or a 333k/s signal.
If you are tuning onto the correct signal with the right settings then you DATV settings window will start coming alive (Large GIF):
It has locked onto a signal when the ModCod indicator turns green. In our example it shows MCOD QPSK 4/5. You will also notice a MER signal indicator at the bottom. In the example it is 8.3. And then lastly, if the signal is strong enough to decode video from it (remember you can lock onto a low signal, but it might not necessarily be strong enough to decode), then the circle next to the video checkbox will turn green.
Once that video circle is green then you can select the Video tab and view your received video live 🙂
You now have the basics working, lets go explore a few other signals. Best way to see which signals are currently active on the transponder is to have a look at the BATC Wideband Spectrum Monitor.
This also tells you what symbol rate the signals are so you can adjust your demodulator settings. Any signals other than the beacon you receive on the Wideband Transponder will have a symbol rate of 1000m/s or less so remember to adjust your bandwidth to the signal you are receiving as well as your symbol rate. Also I found that it locks easier if I zoom into a signal on the waterfall.
Here is a 333 k/s signal I decoded on the transponder from DC3ZB:
I hope my documenting of the steps made it slightly easier for you to navigate SDRangel and get to the point where you can enjoy transmissions on the QO-100 satellite. Its still a bit glitchy, but it works for playing around a bit. If DATV is of interest to you, then your next step will probably be to get some DATV receiving hardware from the BATC 😉
Tom – ZR6TG