Am 2011-08-10 00:54, schrieb Phil Karn: > It's been suggested that I modify my ARISSat-1 BPSK-1000 telemetry > demodulator/decoder to accept wideband quadrature (I & Q) recordings > like those produced by most of the software defined radios out there. > > This is fundamentally not that hard, but first I need some information. > > How many people could actually use this?
I guess all people that use SDRs in the style of FCD, like SDR Widget, or generally all DDC receivers that work with soundcard interfaces. > What is the format of the > recorded files? Is there a standard, or does each make of SDR produce > its own? Often the I and Q channel are recorded via Left and Right of a sound interface, either built-in in the computer or via USB. FCD for example is not more than a very powerful DDC chain, an USB audio device with 96kHz bandwidth and a USB HID interface to control all the settings, like filters and gains. So for a recording you'd probaly end up in whatever your recoding program produces, likely WAV, but any format with 16bit and 2 channels would do. For decoding please be aware that I/Q via sound interfaces has a weak spot at the centre frequency. The interfaces all have a high pass characteristic below like 30Hz, which means the resulting spectrum has a notch in the middle. You usually would not like to exactly tune the center frequency to the frequency of your interest, but a little below or above. You can see that notch for example at http://www.oz9aec.net/index.php/funcube-dongle/423-funcube-dongle-on-the-air-tests-at-oz7sat With all oscillators being not perfect this can probably be ignored, as you wouldn't end up at the center frequency anyway. For converting audio files I can recommend sox http://sox.sourceforge.net which is quite common in Linux distributions, but as cross platform tool also available for Windows and Mac OS X. It's also available as library. What I wonder is how good BPSK1000 survives speech encoders, like MP3. Is there any experience already? 73 Patrick -- Engineers motto: cheap, good, fast: choose any two QTH: JN77rb http://sat.mur.at/ Patrick Strasser OE6PSE <oe6pse at wirklich priv at> _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
