From LEOs to MEO: Aiming GreenCube

From LEOs to MEO: Aiming GreenCube

I have been intrigued by the GreenCube (MT-CUBE-2, Italy Oscar 117) Medium Earth Orbit (MEO) Amateur Radio Satellite ever since I started noticing plenty of posts on GC on Twitter. It has a large footprint of about 13,000 km, much higher than Low Earth Orbit (LEO) satellites. Once I even tried to listen to the digipeater signals from IO 117, the AMSAT designation for GreenCube, with my IC 2730 FM radio and failed. I was perplexed as I had been able to hear the digipeater signals from Amateur Radio on International Space Station earlier, as a buzzing noise in my radio when ARISS was overhead.

My Twitter friend told me that GreenCube is not an easy bird to hear. I have to track the Doppler shift to improve the odds of hearing it. A sound modem has to be setup for decoding the signal and connected to the computer with appropriate software. Another important downside was that I was using an FM radio while GreenCube has an uplink on Lower Side Band (LSB) and downlink on Upper Side Band (USB)! But later others told me that it is possible to work GreenCube even with an FM radio.

Other requirements mentioned by others was that it requires at least a nine element UHF Yagi and a Low Noise Antenna pre-amplifier (LNA). That is because GreenCube is at more than 10 times the altitude of International Space Station. Adding an antenna pre-amplifier would mandate two other pieces of hardware. A Bias-Tee for powering the LNA and a switching mechanism to bypass the LNA when the PTT is pressed and the power output from the radio goes into the antenna, to prevent damage to the highly sensitive circuit of the pre-amplifier.

Ideal would be to have a cross Yagi with automatic azimuth and elevation tracking as well as automatic Doppler tracking in the radio. Automatic Doppler tracking is currently out of question as my radio does not support CAT (Computer Assisted Transceiver) control as far as I know. Of course, I think I may be able to get away with manual Doppler tracking as GreenCube takes a long time for its pass, typically 90 minutes, compared to 10 minutes of an average LEO satellite, which I am now quite used to for manual Doppler tracking using the live display on Argentinian Amast webpage.

As always, I am thinking of limited setups to try out, like my LEO setup which started off with a vertical, omnidirectional VHF only antenna and later moved to a Moxon Dual Band Yagi with a single feeder for VHF and UHF. That too without a rotator, kept on a short mast, at a fixed azimuth and elevation, pointed towards the azimuth of maximum elevation of the satellite pass.

Limited setup would mean also limited success as I am able to work fewer LEO satellite passes than my peers! My search led me to an RTL-SDR.COM webpage which mentions that Matt, from the TechMinds YouTube channel was able to receive GreenCube packets with his omnidirectional terrestrial antenna. But he had used a different radio setup. He was using SDRPlay RSPdx as receiver, SDR++ as receiver software, SoundModem as the packet decoder and GreenCube Terminal for displaying the messages.

GPredict software was used for tracking the satellite and Doppler compensation. So only one part of his setup is there with me at present, the omnidirectional terrestrial antenna! GPredict is a free software, but I could find only Linux and Mac Os X versions. I have stopped using Linux ever since Windows XP was released and my MacBook Air had packed off long back! So I was back to square one.

OZ9AAR has a Terminal Program which supports GreenCube, CUBEBEL-2, LEDSAT and ISS. He has mentioned that UZ7HO makes a very nice SoundModem for Greencube, which decodes and encodes the digital traffic using the soundcard of a personal computer. UZ7HO also makes a terminal program for sending and receiving messages from GreenCube via the SoundModem. The terminal program by OZ9AAR has additional features which would allow discovery of new grids and stations which have not been worked before. Fortunately for me, Terminal Program works on Windows!

Next I came across an article by ZR6TG on Adventures with GreenCube Satellite. He was using 70 cm Wimo X-Quad antenna along with a homebrew rotator. He has mentioned that though he could see data packets from GreenCube without a pre-amplifier, he could not decode it. There is also a mention that others have used a setup as simple as the common dual band arrow antenna.

So I have a little hope that I could at least see the packets with a limited setup, if I homebrew a better antenna. It has been written that SoundModem includes a version for FM reception as well as SSB reception. Does that mean that my FM radio can be used for this purpose? Anyway, I am continuing my search and hope to come up with a solution sooner or later.