I have been quite busy during the last weeks doing overtime at work, nonetheless, I have managed to carry out some small on the air tests of my newly acquired WBX transceiver boards for the USRP and GNU Radio. Tonight, I tuned in to Copenhagen VOLMET that transmits AM on 127.000 MHz.
I had a few hours to spare tonight and I decided to do a quick check of the WBX receiver. Didn’t have time for much so I just compared it to the TVRX tuner using a strong FM broadcast station. The software was a simple WFM receiver constructed in the GNU Radio Companion graphical editor.
As you can see, both receivers have roughly 40 dB SNR, though the WBX seems to be slightly better. I also observed that the WBX has a “flatter” spectrum profile than the TVRX in particular at wider bandwidths.
Tonight I have been testing some ham radio transceiver code written in Python/GNU Radio. It is some student project published on SourceForge. You can find the code on the project page at Sourceforge: http://sourceforge.net/projects/sdr.
This page provides an overview of the various projects and experiments I am or have been doing with GNU Radio and the Universal Software Radio Peripheral (USRP). GNU Radio is a free, open source software development toolkit that provides the signal processing runtime and processing blocks to implement software defined radio. The USRP provides a flexible and cost efficient hardware platform that can be used with GNU Radio to convert the digital data to radio frequencies and vice versa. The USRP and various RF daughterboards, covering most of the DC to 6 GHz spectrum, can be purchased from Ettus Research. Schematics and firmware sources are available under open source license.
My projects with GNU Radio and the USRP are in the field of amateur radio and space communications. The idea is to achieve a broad range of functionality by using different hardware and software configurations. For example, using the same hardware I can switch between narrow band voice communications (SSB/FM) and digital high definition video broadcast using 8 MHz bandwidth by simply switching the signal processing software.
- Gnu Radio Companion Examples
- Gqrx AM, FM, SSB, AFSK, BPSK receiver powered by GNU Radio and Qt
- Simple DVB setup
More GNU Radio / USRP hardware and software projects will be added as they become available. You can also follow my GNU Radio blog if you want to keep up to date with my work in this area (dedicated RSS or Atom feeds available), or you can view the complete blog archive.
I hope these projects demonstrate the power of open source hardware and software.
I made good progress with the portable S-band ground station this week.
I took the receiver to the OZ7SAT lab to measure its performance. Using the USRP+DBSRX and no LNA we could easily detect a -132 dBm CW signal with modest FFT integration (fraction of a second) in a GNU Radio spectrum scope. Using the LNA we could go down to about -138 dBm, i.e. an improvement in SNR of 6 dB. These figures were measured at an SNR ~5 dB. This is excellent, but please note that this is not real “sensitivity” in the traditional sense because we were not demodulating or decoding the signal. We were simply integrating the spectrum for a fraction of a second to detect the presence of the signal. The measurements were done by sampling a 250 kHz wide spectrum.
In this new video blog I am introducing a new project that has kept me occupied for a few weeks now: A low cost S-band ground station for receiving signals from NASA’s lunar spacecrafts LRO and LCROSS. More info at Receiving LRO and LCROSS. Based on the Universal Software Radio Peripheral (USRP) with DBSRX daughterboard, a super low noise preamplifier from Kuhne and GNU Radio software.