Video recording of the HO-68 / XW-1 Chinese amateur radio satellite in linear transponder mode on November 9, 2010. Recorded using the Universal Software Radio Peripheral (USRP) with RFX400 daughterboard and GNU Radio software receiver.
GQRX receiving the HO-68 satellite
The gqrx software receiver implemented with GNU Radio and Qt GUI is now taking shape and becoming useful. Yesterday evening I went to OZ7SAT and had the USRP+WBX connected to a real antenna tracking amateur radio satellites. The video below shows reception of the evening pass of HO-68, aka. XW-1.
A patch to fix audio_alsa_sink[hw:0,0]: snd_pcm_hw_params failed
Last night, while I was preparing for the AMSAT-OZ satellite weekend, I noticed that my gqrx receiver didn’t work very well on my laptops. Every time I tried to change operating mode the receiver stopped with a runtime error:
audio_alsa_sink[hw:0,0]: snd_pcm_hw_params failed: File descriptor in bad state
terminate called after throwing an instance of 'std::runtime_error'
what(): check topology failed on audio_alsa_sink(1) using ninputs=1, noutputs=0
This happened on both my Acer and my MacBook Pro; both running the lates git of GNU Radio v3.3.1git-96-g1fa9a8ea. This was bad news because I was hoping to show off my new software receiver with Qt GUI during the weekend. Fortunately, there is an easy workaround that eliminates the problem.
The downsampling experiment
As I mentioned in my previous post, my “optimizations” of the multi-mode receiver code caused a sudden loss in performance.This was a big surprise because what I did was to replace two filters with only one, which I would expected to yield a performance gain and certainly not a loss. What happened at the same time was that the sample rate in the demodulators went from 50 ksps to 250 ksps and it was the responsibility of the demodulators to downsample this to 50 ksps. I suspected that this might have cause the increased CPU load and I have set up a simple experiment to confirm it.
AM/FM/SSB software receiver with Qt GUI
I have been a bit quiet over the last few weeks but don’t you worry, it is only because I have been busy and I can now present you what I have been tinkering with during the last few weeks: An AM, FM, SSB and CW receiver implemented using GNU Radio (python) and Qt graphical user interface.
Ubuntu 10.10 on the Acer Aspire 5745G Laptop
Now that Ubuntu 10.10 is out I am slowly upgrading my computers one by one. Today it was time to perform the upgrade on my newest (in terms of technology) and most bad ass computer, the Acer Aspire 5745G Laptop. I have previously written about running Ubuntu 10.04 on it, which was the first Linux OS I have installed. Already with Ubuntu 10.04 everything was working and only the Ethernet interface required manual installation of driver. Installing Ubuntu 10.10 was a simple matter of performing the upgrade from within the package manager.
Automatic update in the sky at a glance view
The Sky at a glance time line view in Gpredict 1.3 is updating itself as time passes. This video demo shows this feature in highly throttled simulated real time mode as well as in manual time control mode.
NOAA 18 and 19 APT images Sunday, 17 Oct 2010
A few APT images received from NOAA 18 and NOAA 19 yesterday. THe setup I used was the very same that I have described earlier. Click on images to see full resolution and image details.
Gpredict 1.2 released
After one year of development, bug fixing and testing we have decided that it was time to make a new release of Gpredict. This release features several new features such as the rewritten layout engine as well as lots of bug fixes.
Gumstix OVero Fire and Tobi after the crash landing
As I mentioned last week, the Gumstix Overo Fire COM and the Tobi expansion board looked surprisingly well after the crash landing of the failed rocket. Yesterday, I have had a chance to take a closer look at the boards and see what damage has occurred to them. Once I separated the two boards from each other it was obvious that the 70 pin AVX connectors were damaged on both board. The electrical connections on the Gumstix Overo Fire are still OK despite the damaged connector, but the Tobi board got damaged beyond repair (PCB tracks ripped off). Below you will find some close-up photos and a video about the damaged connectors.