The signals from the satellite are not very strong, so some care must be taken when you want to receive them. The stronger spot beams will be relatively easy to receive, while some of the fainter ones will take more effort.
Antenna¶Basically any antenna design that provides:
- Good directivity (good gain)
- Left Hand Circular Polarization (LHCP)
The first captures were made using a 80cm offset dish. While it provides very good gain / directivity, it's not the most transportable :)
The helical antenna is a good choice because it's fairly simple to build with easily obtainable materials. A good online tool to compute the parameters of the helix is here : http://www.rac.ca/tca/2006-01%20Helix%20Design%20Calculator.html
Another very simple design is a biquad (TODO: Add link)
This is optional and not required for many of the stronger beams.
If you choose to use one, you need to make sure it's good for your band of interest and that it won't saturate (either itself, or the chain following it).
A good option is the LNA-23-BP from dg0ve ( http://www.dg0ve.de/ ) because it includes a 60 MHz bandpass filter. For a small fee you can get it retuned to 1550 MHz.
Again, optional. It helps prevent possible saturation of your capture device input stage in case you have strong signals in your neighborhood. Note that some LNA will have integrated filters for their band of operation.
Any SDR capable of capturing the frequency band of interest ( 1532.5 to 1554.5 MHz for downlink ) should work.Currently the most used ones are:
- Any Ettus hardware ( http://www.ettus.com/products )
- It's been tested with WBX, but should work with other daughter boards ( SBX / DBSRX / DBSRX2 / RFX1800 )
- FunCube Dongle Pro ( http://www.funcubedongle.com/ )
- Cheap and easily transportable. Can capture up to 3 contiguous GMR-1 channels at once.
Examples of working chains¶
FunCube Dongle Pro + helical antenna¶
This setup uses a FunCube Dongle Pro along with a helical-antenna. Works fine without external LNA and the FCD gain set to 30dBm.
USRP + WBX + helical antenna¶
This setup works without any specific LNA, simply by using a USRP board with WBX front-end and a helical antenna.
If a better signal is needed (receive fainter beams), a LNA from DG0VE (see above) works great at providing both gain and filtering unwanted signals.
USRP + WBX + LNA + offset dish antenna¶
The signal chain looks as follows:
- 80cm offset dish
- selfmade RHCP feed (4 turns)
- LNA BB 1020 A from Kuhne electronic (>28dB gain, 0.8dB NF)
- L-Band dielectric filter
- WBX with GDB (gain setting at 20dB)
- USRP1 with standard clock
It is extremely helpful to observe the waterfall display while moving the dish. When adjusting for best reception, you have something like 10 degrees of margin in H and V direction. Gpredict has been used to evaluate Thuraya bearing with good results. You may use http://www.dishpointer.com and http://goo.gl/maps/ugMCd for Thuraya 2 or http://goo.gl/maps/Z3Q5O for Thuraya 3 as an alternative.
The antenna feed was built following the guidelines from http://www.uhf-satcom.com/lband/. Please note, that Thuraya uses LHC polarization, so the feed has to be RHCP because of the mirroring dish.