Forum: GNU Radio Trying to decode 2-gfsk from TI CC1125

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876f3f6515f1e476fc6d71239addf992?d=identicon&s=25 Juho Salmio (lagstorm)
on 2016-01-23 17:03
Attachment: flow_graph_and_sample_data.zip (3 MB)
Hi,

I'm trying to decode data transmitted by TI cc1125
http://www.ti.com/lit/ug/swru295e/swru295e.pdf radiochip and received
with hackrf. The transmission is using 2-gfsk modulation and the
transmissions are encoded with TI:s own packet format. The symbol rate
is 9600 ksps. The preamble is 6 bytes of 0xAA.

My current pipeline in GNURadio is:

file source -> throttle -> low pass filter -> simple squelch ->
quadrature demod -> clock recovery MM -> binary slicer -> Correlate
Access Code Tag -> Tag Debug.

The problem is that the "Correlate Access Code - Tag" can't find the
preambles.

If I use Scope Sink after the Quadrature Demod I can clearly see the
preamble pattern from the sink.

For testing purposes I changed the the deviation of the transmission to
its maximum value (300kHz), but that didn't help either. The sample data
is recorded with that deviation and the flow graph uses that sample
data.

Is there something obviously wrong or incorrect in my graph? I also
don't really understand the effect of the parameters in Clock Recovery
MM.

I have tried to use the low pass filter and squelch to remove the noise
from the signal.

This is my first time trying to do something with GNURadio and radios in
general so still trying to wrap my head around all the new stuff.

Any suggestions or ideas what I should try next?

-Juho
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