Connecting to GNU Radio via ZMQ

The latest code base of AIS-catcher can take streaming data via ZeroMQ (ZMQ) as input. This eases the interface with packages like GNU Radio. The steps are simple and will be demonstrated by decoding the messages in the AIS example file from here. AIS-catcher cannot directly decode this file as the file contains only one channel, the frequency is shifted away from the center at 162Mhz and the sample rate of 62.5 KHz is not supported in our program. We can however perform decoding with some help from GNU Radio. First start AIS-catcher to receive a stream (data format is complex float and sample rate is 96K) at a defined ZMQ endpoint:

AIS-catcher -z CF32 tcp://127.0.0.1:5555 -s 96000

Next we can build a simple GRC model that performs all the necessary steps and has a ZMQ Pub Sink with the chosen endpoint: Running this model, will allow us to successfully decode the messages in the file:

The ZMQ interface is useful if a datastream from an SDR needs to be shared and processed by multiple decoders or for experimentation with different decoder models with support from GNU Radio.

Note that with CSDR and SoX we can also decode this file as follows:

sox SDRuno_20200907_184926Z_161985kHz.wav -t raw -b 32 -e floating-point - |csdr shift_math_cc 0.165 | AIS-catcher  -r cf32 . -s 62500 -c X -v