I was reading about the probability density function when I suddenly realised what the histogram sink in GNU Radio can be used for. I knew very well what a histogram is and how it used in e.g. physics, I just didn’t quite know what to use it for in a software radio.
Month: August 2010
Broken RFX1200 and more sensitivity measurements
I went to OZ7SAT today to do some measurements on the receiver boards. I wanted to see how the sensitivities compare to that of the WBX receiver that I have measured earlier using a CW signal and SSB receiver. The criteria was again to find the weakest signal that I could both hear and see on the spectrum scope and that I would be able to decode if it was a Morse code transmission. The limiting parameter is actually the spectrum scope, because I can hear tones much weaker than what is visible on the 512 channel FFT scope.
Webcam pixel formats and Gstreamer caps filters
Up until now I have been using the standard (link) YUV 4:2:2 pixel format with my Logitech Webcam Pro 9000. This format is good for most cases; however, the framerate is limited to 15/2 fps at 1280×720 resolution, while the other supported formats (MJPG, RGB3, BGR3, YU12, YV12) support this reolution with up to 30 fps! So it was time for me to figure it out.
GstInputSelector to switch between different cameras
An email on the gst-devel mailing list last week pointed me to a rather interesting example in the gst-python repository: switch.py – shows how to use the GstInputSelector element in a Python script to select between different input streams. When I looked at the example I thought right away that it would be cool to use it to switch between different cameras in my simple DVB setup that uses Gstreamer and GNU Radio.
Pulseaudio device names
Recording audio with gstreamer is easy:
gst-launch -e pulsesrc ! audioconvert ! \
lamemp3enc target=1 bitrate=64 cbr=true ! \
filesink location=audio.mp3
The pulsesrc element here refers to the pulseaudio input (pulseaudio is AFAIK the default sound system in all linux distributions nowadays). This is good and will capture audio from the default sound input, which can be microphone or line-in depending on the hardware and the pulseaudio configuration.
But what if I plug in my USB webcam with built-in microphone and I want to capture audio from that?
Simple SSB transmitter using complex bandpass filter
There are several ways to generate a single side band signal in a software radio and I am slowly exploring each and every one of them. For this first attempt I have decided to try using a basic amplitude modulation followed by a bandpass filter with complex taps that can select either the upper or the lower side bands.
Full duplex transceiver version of the DVB setup
This weekend I have been playing with a full duplex transceiver version of the simple DVB setup that allows to use only one computer and one USRP as a transmitter and receiver. By using separate daughterboards I can use one side to transmit and the other side to receive. Using two sets and two frequencies the transceiver can be used for two-way video conferencing over the air 🙂
GNU Radio presentation
The slides from my presentation about GNU Radio and the Universal Software Radio Peripheral given at the AMSAT UK colloquium on August 1, 2010. A video recording is also available at http://www.batc.tv/ under archived videos.
Simple DVB with Gstreamer and GNU Radio
I have had this idea of using my webcam for digital video transmission for quite some time now. Capturing and processing video from UVC webcams has been a routine for a long time and I have had great success with Logitech webcams (the 9000 series) that have great UVC support. I still had a problem though with finding a good way to interface the GNU Radio transmitter and receiver to the video processing pipeline implemented in Gstreamer.
In my experiment with receiving packet radio from the ISS I used a named pipe to create a real time interface between the GNU Radio receiver and the packet decoder multimon. I decided to try this trick for sending video in to and out of GNU Radio and it works! The following experiments were implemented and executed on the 27th and 28th of July with some minimal preparation on the 26th.