Packet radio from the ISS with GNU Radio and USRP

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.

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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.

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Satellite Tooltips

Satllite tooltip in GpredictYou 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.

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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.

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Ubuntu Linux on the Acer Aspire 5745G Laptop

Info icon 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.

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