I have been having some fun playing with DATV on Oscar 100 lately. As DATV isn’t really a thing in South Africa the satellite has given me the opportunity to get a bit more involved in the DATV scene. If you are interested in DATV then the BATC should definitely be your first stop on learning more. A lot of the developments I have been doing would not have been possible with their hardware projects and the many people involved.
DATV Reception on Oscar 100
Minimal hardware is required to receive DATV from the wideband transponder:
- A satellite dish. I’m currently using a 1.2m dish for reception
- An LNB, any new recent LNB should work just fine. You will need to power the LNB using either a Bias-T or from the Minitiouner. I prefer to power it separately as I also use if for the narrowband transponder. The LNB does not need to be GPS disciplined for DATV use, but it does need to be horizontally polarized. This can be done by either powering the LNB with 12v and then turning it 90 degrees, or alternatively most LNB’s can have their polarization switched by changing the power supply voltage. For example, on my link I can feed 12v for vertical and 18v for horizontal polarization. I built a simple device for easy switching between the two (vertical is required for the narrowband transponder).
- Minitiouner, this hardware kit from the BATC consists of a tuner (very similar to ones found in a set top box) and a computer USB interface. Its a fairly low cost, easy to build kit.
- Minitioune Software developed by F6DZP. This is the software that interfaces to the Minitiouner over usb to control the tuner and receive DATV
With those bits and some careful alignment you should be able to receive DATV easily. It is normally recommended to tune the pointing of your dish to the narrowband beacons first and then finetune for the wideband beacon. The bigger your dish the better reception you should have, but a bigger dish means your pointing should be a lot more accurate. With that you should be able to receive DATV from Oscar 100 easily.
Networking and Longmynd
Most of my Amateur Radio equipment is networked one way or another. I prefer it this way because it means I’m not chained to being in the shack when I have time to play radio. I started looking for some options for my DATV reception (Winter is coming and it would be a lot more fun to watch the different weekly nets on Oscar 100 from my bed). After some reading I ran across Longmynd. Its basically similar to Minitioune in that it can be used to control the tuner and receive the TS streams from other DATV transmissions. Its a command line application and once it is setup you would use something like VLC to view the received and decoded data. The original version of Longmynd was developed by Heather Lomond and there are various forks modified for specific purposes (Ryde, Portsdown, etc). The one I specifically found very interesting was the fork from Phil Crump who started experimenting with adding a web interface to Longmynd. The web interface was interesting because he had developed a websocket interface to get status messages and send control messages.
This gave me an idea on how I can make a client for a networked DATV receiver. The concept was to take a Raspberry PI (if you can find one) put it on the network and hook a Minitiouner to it. The Raspberry PI is installed with the modified Longmynd version. I then developed a small client application that would send commands over websockets to the Longmynd to get status messages and then send control commands (Change frequency, symbolrate, etc). The Longmynd would send back the received TS stream for display in the client. The Longmynd-Client was born (need to come up with a better name)
The client is fairly basic, it shows the normal parameters associated with a DATV reception. Along the way I’ve included added improvements such as showing the Oscar 100 Wideband Spectrum (based on the Quick Tune application from Rob Swinbank), saving snapshots and even some basic dish calibration features. Most of the additions are from suggestions from various radio amateurs who have been using it and helping me test it. As the features have been added I needed a few more features implemented on the Longmynd. Phil has graciously been adding more commands to his Longmynd version for use by the client. Thanks Phil!
The latest version and setup instructions will always be available here.
This works pretty well and I can now access and view the DATV transmissions I receive anywhere on my network with a PC. Unless you have configured Longmynd for multicast UDP you can only receive a video feed on 1 pc at a time, so the software will tell Longmynd where to send the feed based on which client sent a command last. With multicast all the clients can view the same stream at the same time, but it doesn’t work on all networks and can be tricky to setup. The client makes provision for both based on your settings.
Another fun feature is the decoding of the callsigns which now show on the spectrum, but also generates an output via a websocket to control other software. For example, I’ve got it setup to auto tune during the day, every succesful decode translates into a message going to a Node-Red installation which then filters out the callsign from a favourites list and then sends me a Telegram message when that person is transmitting on the satellite. This works great, but I had to change it a bit when I started getting messages at 2am 😉 (Looking at your Martin – G4FKK).
With the basic client working well, my thoughts went to other platforms where I can do the same. Why drag around a laptop when I can do the same on my phone or tablet? The next experiment turned to Android and using Flutter to develop a Longmynd client for my android phone. The current version is still very experimental, but the concept works.
Selection of signals on the Wideband works a bit different in that instead of showing the whole spectrum it just shows buttons for the various active transmissions.
Saro (VU2OBR) has even been testing it by loading the client on an Android TV which seems to work very well.
The client has been fairly successful and the experiments have lead me to a few more ideas. First off I would like to swop the Minitiouner + pi for a Winterhill Receiver. The Winterhill receiver is essentially the same concept but it is a single solution with two tuner modules and an “embedded” Raspberry PI designed by Brian (G4EWJ) and Mike (G0MJW). A single tuner module can receive and decode 2 transmissions, so with the Winterhill receiver I can now receive 4 streams at the same time. The Android TV experiments have also lead to start developing an Android version, specifically for Android TV’s or cheap Android TV Boxes which could almost work similar to the Ryde receiver, but networked.
I have also recently received all the bits and pieces for a Winterhill Receiver and have got it up and running. Development around similar software for it has begun with the help of Brian Jordan (G4EWJ).
I’m still a newbie when it comes to DATV, but it certainly is a fun aspect of our Amateur Radio with lots of opportunity for experimentation and DIY projects.
I would also like to thank all the amateurs who have helped with testing the various weird software I’ve been putting together and also to everybody who has been buying me beer.