Wednesday, October 22, 2008

Rover Concept Prototyping

This prototype rover was cobbled together by Joerg Schnyder as a proof of concept for Team FREDNET's lunar rover. Even though it is built completely out of reused parts, it performs quite impressively!

Sunday, October 19, 2008

Slow Scan TV Transmission from the International Space Station

Saturday at 10:05 UTC we successfully received a Slow Scan Television transmission from the International Space Station. The receiver chain consisted of the USRP+TVRX, GNU Radio software for demodulating the FM signal into audio, and the freely available Digital Master 780 for decoding the SSTV data.

The transmitted picture was taken with a camera onboard the space station looking out through one of the windows. NA1SS is the amateur radio callsign used by US astronauts while they are on the space station.

SSTV picture from the International Space Station

Richard Garriott has been very active on amateur radio ever since he arrived at the space station. Besides the SSTV activities he has been having voice contacts with schools and radio amateurs around the world. You can listen to Richard making voice contacts with radio amateurs in Europe in this recording.

Thursday, October 16, 2008

VHF/UHF Receiver

The picture below show a VHF/UHF receiver assembly based on the Universal Software Radio Peripheral and a standard TV-tuner. The board on the left is the S-band transceiver module described earlier.

VHF/UHF receiver

The TV-tuner based VHF/UHF receiver can receive a 6MHz wide RF spectrum anywhere in the range 50-800MHz. It has a noise figure around 8dB, which is not good enough for Lunar comms; however, it is a good cheap starting point for breadboarding and experimentation. Using a modest yagi antenna and a low noise preamplifier, we have been able to receive signals from low Earth orbiting satellites.

Sunday, October 12, 2008

Expedition 18 lift off

Early this morning, Expedition 18 successfully lifted off from the Baikonur Cosmodrome in Kazakhstan. The Soyuz TMA-13 spacecraft, carrying U.S. astronaut E. Michael Fincke, Russian cosmonaut Yury Lonchakov and spaceflight participant Richard Garriott towards the International Space Station, is scheduled for docking to the Zarya module on 14 Oct 2008 around 9:30 UTC. NASA TV will provide live coverage of the docking event.

Image Credit: NASA/Bill Ingalls

Richard Garriott - son of former NASA astronaut Owen Garriott - has a tight schedule carrying out scientifc research and educational projects. Amongst his plans is to have live amateur radio contacts with various schools around the world using his amateur radio callsign W5KWQ. His stay on the space station also coincides with the annual Jamboree on the Air (JOTA) event giving scouts around the world an opportunity to talk with astronauts onboard the station. Something that makes Garriott's trip particularly interesting for us is his plan to turn on the on-board slow scan television equipment that will perform automatic image transmissions in Robot-36 mode.

While slow scan television is not a technically feasible option for a Lunar mission nowadays (despite the fact that it was used by many of the early Lunar missions) this event will provide an excellent opportunity to test some of our early prototypes for ground equipment using real signals from space. The International Space Station is a very fast moving object and successful reception of the images will require proper tracking with directional antennas and active compensation for the Doppler shift, caused by the high relative velocity between the space station and the receiver on Earth.

There are many external factors that might prevent this experiment from being successful. The most significant is whether the slow scan television equipment will be turned on while the space station passes over our ground station and this is, of course, out of our control. In either case, we are very excited and are looking forward to this event.

Friday, October 10, 2008

Transceiver modules for the L and S bands

The RFX1200 and RFX2400 daughterboards provide complete radio frequency transceiver interfaces for the Universal Software Radio Peripheral in the L and S bands. The receivers have an AGC range of 70dB. The transmitter output is around 200mW for the RFX1200 and 50mW for the RFX2400. The transmitter and receiver frequencies can be controlled separately (split mode) and the boards are also capable of full duplex operation.

Saturday, October 4, 2008

Universal Software Radio Peripheral

The Universal Software Radio Peripheral (USRP) is an open source hardware device from Ettus Research and it is designed to allow general purpose computers to function as high bandwidth software radios. Its primary function is to serve as a digital baseband and IF section of a radio communication system. The basic design philosophy behind the USRP has been to do all of the waveform-specific processing, like modulation and demodulation, on the host CPU. All of the high-speed general purpose operations like digital up and down conversion, decimation and interpolation are done on the FPGA.

The USRP has four 64 MS/s 12-bit ADCs, four 128 MS/s 14-bit DACs, four digital downconverters with programmable decimation rates, and two digital upconverters with programmable interpolation rates. It uses a USB 2.0 interface (480 Mb/s) and is capable of processing signals up to 16 MHz wide. The modular architecture supports a wide variety of RF daughterboards as well as auxiliary analog and digital I/O.

Currently, Team FREDNET uses the USRP together with GNU Radio as an open source platform for prototyping and testing communication subsystems.