On July 10, 2010, I was listening to the linear transponder downlink of VO-52 when I suddenly noticed a very strong peak about 50 kHz below. I checked Gpredict and found out that it was the APRS downlink from the International Space Station RS0ISS on 145.825 MHz. Thanks to the flexible GNU Radio framework and the USRP, I could easily receive both satellites at the same time as shown on the video below.
Alexandru Csete
Patched AGC2 block and updated SSB/CW receiver
You may have noticed the weird construction I used in the SSB/CW receiver V0.7 implemented in the GNU Radio companion. It was using three AGC2 blocks with different decay rates, running in parallel and selecting one of them using a selector. The reason why I didn’t just use one block and set the decay rate of the block using an option menu or a slider was that this method didn’t work! Today I decided to dig deeper into the code and see how to fix this.
The solar eclipse of July 11 – as seen by AO-51
On July 11, 2010, a total solar eclipse could be observed in the southern Pacific Ocean. During the eclipse, the AO-51 amateur radio satellite was entering daylight, coming in over South America. When AO-51 enters daylight the solar arrays start charging the batteries. This can be observed in the telemetry as a sudden increase of … Read more
Satellite Tooltips
You may have already seen tooltips in the Gpredict user interface. I have made extensive use of them for providing short description of the functionality of the GUI controls all over the application. Lately, I have felt a desire to extend the usage of tooltips to also include graphical objects like satellites shown on the map or the passes shown in the “Sky at a glance” module.
Gpredict uses GooCanvas for graphics, which adds a the “missing” 2D canvas library to Gtk+. Since version 0.15 GooCanvas includes support for Gtk+-like tooltips for any objects on the canvas. This is really great since it simplifies the effort from messing with own popup windows to using single line API calls.
Gstreamer compositing using the GstvideoMixerPad properties
Few weeks agio I posted my notes about picture-in-picture compositing in Gstreamer using nothing else than the gst-launch command line tool. I also wrote that I could not figure out how to use the xpos, ypos, zorder properties of the GstVideoMixerPad element. I got a comment on this note from Jan Schmidt telling that these properties can not be used with gst-launch but are easily accessible from Python. He also gave a very cool example that shows how to use it.
More NOAA APT Images with GNU Radio, URSP and WBX
Last weekend I wrote about my spontaneous experiments with receiving and decoding APT transmissions from NOAA polar orbiting weather satellites. This weekend I decided to extend the experiments by trying to receive at very low elevations and get images from far away.
Embedded USRP and Gumstix Overo COM Clusters?
Just a quick note about some exciting news I have heard. Thanks to Google Alerts I learned about this interesting press release from Gumstix, announcing the Stagecoach expansion board, which creates an OMAP computing cluster of Gumstix Overo COMs.
Ubuntu Linux on the Acer Aspire 5745G Laptop
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This article is about running Ubuntu Linux 10.04 on the Acer Aspire 5745G. If you are interested in running Ubuntu 10.10 check this article instead. |
It was time for me to get a new computer and this time I was going for laptop with a fast CPU and sufficient Nvidia graphics that is suitable for video processing and high bandwidth software defined radios. Didn’t want ATI graphics because I have bad experience with ATI and Linux. Nvidia on the other hand has been working very well for me on Linux.
I thought of getting a new Macbook Pro 15″ with and Intel i7 dual core processor, but I ended with the Acer Aspire 5745G-724G50Mn with an i7 quad-core, 4GB RAM and a Geforce GT330M with 1 GB VRAM. The rest of this article describes my first experiences with installing and running Ubuntu Linux 10.04 Lucid Lynx 64 bit on this computer side by side with the pre-installed Windows 7.
NOAA Weather Satellite Reception with GNU Radio and USRP
This weekend I ended up receiving APT signals from NOAA polar orbiting weather satellites. I only wanted to explore IQ data recording and playback with GNU Radio but when I first used NOAA 15 as test signal and saw what I could receive I got slightly distracted from my original plan.
Playback of the Recorded IQ Data
Yesterday I described how to record the IQ data from the USRP focusing on generating unique file names every time the GNU Radio / GRC script is executed. Playing the recorded IQ data is really simple: We take the corresponding receiver application and replace the USRP source with a file source and a throttle block.