Qtmm souncard modem decoding APRS data from the ISS

Yesterday I successfully received APRS transmissions from the International Space Station on 145.825 MHz using my Yaesu FT-817 connected to my MacBook Pro via a Signalink audio interface and a USB sound adapter.

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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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