I am attempting to read samples of an off-air DVB-T transport stream into
an IQ file for offline analysis but can't get it to work at all.
I can run the dvbt_rx_8k.grc example which reads the adv16.cfile IQ TS
file produced by Ron Economos, displays the FFT and 16 QAM constellation
and produces a valid .ts file which can be played with a video player..
I adapted that example flow-graph for a local off-air MUX with parameters;
64QAM, 2/3 rate, 1/4 guard interval, 8K FFT. The FFT displays OK but the
constellation graph does not work and show the expected 8 x 8 matrix --
instead it shows just a single dot in the middle.
This
https://www.mklab.rhul.ac.uk/~tom/tvdx/gr/dvbt_rx_8k_64QAM_chD44-live.grc
cut-down demo attempts to sample channel channel D44 live using an
RTL2832/E4000 USB stick. I have also tried using the rtl_sdr
dump-to-IQ-file utility and converting the format from 8-bit uint into
32-bit float (complex) using the sox utility, eg.
rtl_sdr -f 658000000 -s 2800000 -n $[280000*60] chD44.raw
sox -t raw -r 2800000 -b 8 -c 1 -e unsigned-integer chD44.raw -t raw -r 2800000
-c 1 -e float chD44-sox.raw
using a sample rate of 2.8M here, and processing the resultant IQ file
with grc but the result is the same.
I also tried with a 3.2M sample rate, the maximum permitted value with
RT2832 USBs sticks but again without success.
Am I doing something wrong in grc or it is just that these sample rates
are nowhere near sufficient for the whole-MUX type of data I am attempting
to capture?
I was able to adapt the dvbt_rx_8k.grc demo for a 64QAM file (adv64.cfile
also from Ron Economos) and process that OK in grc.
Many thanks
Tom Crane
--
Tom Crane, Dept. Physics, Royal Holloway, University of London, Egham Hill,
Egham, Surrey, TW20 0EX, England.
Email: t.cr...@rhul.ac.uk
Fax: +44 (0) 1784 472794
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