GQRX C++ Edition

About a week ago I resumed working on GQRX – an experimental AM/FM/SSB software receiver powered by GNU Radio and using Qt for user interface. This time, however, I am not going to continue working on the Python receiver but create a new receiver from scratch written in C++. It will support Funcube Dongle and USRP/UHD devices.

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Simple APT decoder prototype

I have wanted to implement a simple APT decoder for the NOAA weather satellites in GNU Radio for quite some time now, in particular since the USRP equipped with a TVRX or WBX daughterboard and a GNU Radio FM receiver can be an extremely good receiver for this purpose. Today I have spent some time looking at the details of decoding APT and actually ended up with a working prototype implemented using the GNU Radio Companion.

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Test driving Quisk SDR

Before getting my hands all dirty with adding UHD driver to Quisk, I decided to take it for a test drive using some pre-recorded samples. I have used a 250 ksps recording of the HO-68 / XW-1 linear transponder downlink that I have recorded on November 9, 2010 using the USRP and the RFX400 daughterboard.

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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.

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