Current approach
As DVB-T is potentially problematic in regard of doppler shift, we want to use DVB-S. That makes the use of COTS parts difficult, as DVB-S modulators are not available in small sizes and are more expensive. With the availability of the LimeSDR Mini we have a cheap option of a radio module and can use a Raspberry Pi 3 for the creation of the bitstream. For now we will use only one-way communication.
The solution will be using a 5V power-rail (should be attached directly to the Raspberry Pi 3). At this moment we did not decide on a particular frequency (e.g. 900MHz or 1.2GHz band), so we do not have a specific PA yet. On the ground we will use a LimeSDR or a BladeRF to receive the signals.
As a sideproject we might have a intra-Rocket communication using BT and a extra-Rocket communication using WiFi (e.g. on the Launchpad). The Video Downlink System should be regarded as a potential fallback telemetry downlink system.
https://github.com/PiSupply/PiJuice
Old Idea
From a discussion between Charlie and Dennis.
HAM radio people use the DVB-T or DVB-S protocol for DATV (digital amateur TV) in Europe and in US (e.g. https://batc.org.uk/). There are commercial products which encode a hdmi picture and send it out over a DVB-T channel.
A device which we could use would be this one: http://www.hides.com.tw/product_HV320_eng.html (there are multiple available, unclear what kind of different features they offer).
Rocket Inventory:
- 3x Raspberry Pi 0 with camera (beware, need special camera cable: https://www.adafruit.com/product/3157)
- HV330 without PA (or with PA?)
- PA (needs to be a PA which supports wide bandwidth and digital modes. CW/SSB PAs are problematic)
- Antenna
Ground Station
- Notebook
- USB Receiving Adapter (e.g. UT-164)
- Antenna (multiple Antennas, like Dipol + Yagi + Helix antenna)
Things to discuss:
- Frequency? (D: I would prefer 70cm/440MHz, easier to get PAs and is less problematic in regard to doppler)
- Bandwith? (HAMs usually use 2-4 MHz, commercial products use 5-8 MHz)
- Power? (run the PA+Modulator all the time or only at timeslots)
- COTS solution (HV-330) or partly-selfdesigned solutin (e.g. Intel Quark + UT-210)
- COTS-Solution:
- Pro:
- simple, works reliable, no need to implement the stream protocol
- Con
- only one stream (e.g. interleaved 4 pictures in one picture)
- Pro:
Energy budget
| Device | Input voltage | Power usage | Usecase | Size | Weight |
|---|---|---|---|---|---|
| Raspi Zero | 5V | 240mA Source, 350mA max | Video recording (with camera) | PCB: W(65mm) x D(30mm) | |
| HV-330-A / B | 12V | 300 mA@12V without PA | Encoding, Modulating, Transmitting | PCB: W(42mm) X D(42mm), stacked | PCB: 25g, with PA,Fan,etc: 70g |
Bill of Materials
| Qty. | Device | Weight | Price |
|---|---|---|---|
| 3 | RaspberryPi 0 | 9g | $5.00 |
| 3 | PiCamera Module | 3g | $19.95 |
| 1 | HV-330-A Modulator | 70g (typical) | $280 |
| 1 | Amplifier | ~20g | ~50 |
| 1 | Power Distribution Board | ~40g | ??? |
| X | Heatsinks | ??? | ??? |
| X | Cables | ??? | ??? |
| 1 | Lithium Polymer Battery | ??? | ??? |
| Totals: | ~500g | $550 |
Some material:
https://kh6htv.files.wordpress.com/2017/12/an-28a-hv320rev18dec2017.pdf
http://www.von-info.ch/hb9afo/articles/DVB-T/HV320/HV-320_Transmitter_Box_QIG_v1.0_20151001-1.pdf
Experiences (in regard to range, bandwidth, etc): https://www.oe7forum.at/viewtopic.php?f=7&t=410&start=375#p2103, https://www.oe7forum.at/viewtopic.php?f=7&t=410&start=405#p2367
https://www.oe7forum.at/download/file.php?id=2035
Other implementations
...
In an effort to improve the video capture system we're attempting to implement the system developed by Alex Csete at Copenhagen Suborbitals. Charlie G attempting to get G got in contact with Alex regarding his original design. The software repo for the encoder can be found here. The video overview of the system can be found here. The system notably required a custom amplifier designed by Copenhagen Suborbitals. It is unknown if we will be able to access this designwas a two amplifier system designed by Peter Mortensen. The primary amplifier was based on the kit here, however the output power of the HackRF was too low, so an additional amplifier was added to the circuit, and a custom PCB created to minimize the connections.
This architecture implements the COTS DVB-S2 standard for high definition digital video and transmits in the 23cm band (1.3 GHz). Copenhagen Suborbitals saw a very stable link at 3.5W RF at 10km 7 km altitude. Rocket Team believes we have an opportunity to simplify this system by integrating additional COTS hardware.