tetra-demod.py chain pipe error

Jacek Lipkowski sq5bpf at lipkowski.org
Fri Apr 3 08:27:42 UTC 2015

On Thu, 2 Apr 2015, Espectro Digital wrote:

> Thank you very much, Jacek.
> A C version of tetra demodulator would be great.

sorry for my previous post, got the lists mixed up :)

but since i've already answered, here goes:

don't use rtl_sdr with low sample rates (<1Msps), either it doesn't work, 
or works bad. also tetra-demod.py will segfault in 
gri_mmse_fir_interpolator_cc() - and this is the probably the main reason 
for the error that you're seing.

if you want to use rtl_sdr, then the easiest will be to write something 
that decimates the data to 36ksps and feed it to the qpsk demodulator (use 
simdemod2.py if you don't want to write your own). this way most of the 
processing chain will be C (the qpsk demodulator can be exchanged later 
for a c version too, but i doubt this will significantly lower the system 
load). this is on my (long) todo list for telive, because this would allow 
using cheap hardware for listening to a lot of channels at once.

but it depends what you want to use rtl_sdr for. do you want it for less 
system load, or do you want it to have remote control over the receiver. 
in the latter case you can control gnuradio via http. i can post a 
gnuradio flowgraph that i use for scanning tetra networks. the frequency 
is controlled via http from a modified version of telive (scans the 
frequencies and logs the network parameters it finds)


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