CIR scripts

This is a set of script to do correlation measurement measurements of a DAB signal. These scripts can be used to do channel impulse response measurements using a RTLSDR receiver.

Right now there are three scripts:

  • correlate_with_ref.py: Finds the NULL symbol of an IQ file, and runs correlations against the known phase reference to find the components.

  • simulate_channel.py: Reads an I/Q file generated by ODR-DabMod and adds some additional components, somehow equivalent to signal reflexions. Each reflexion has a delay and an amplitude factor.

  • cir_measure.py: Runs a small webserver that does the correlation all the time and updates a webpage

Example image: Example correlation

The image shows the received CIR of a real DAB signal captured with the RTLSDR.


To run the webserver on all network interfaces, receiving on 202.928MHz:

./cir_measure.py --host --port 8080 --freq 202928000

More options are available (gain, number of samples), see the help with

./cir_measure.py -h

Offline processing

To read in a recording using a RTL-SDR receiver, use:

rtl_sdr -f 188928000 -s 2048000 -g 20 -S - | \
dd of=DAB_9A_10_u8_G20.iq bs=2 count=1966080

replace 1966080 (ten Mode 1 transmission frames) by a larger value if you want.

Then feed the data to the script

./correlate_with_ref.py u8 DAB_9A_10_u8_G20.iq


librtlsdr and its tools.

Python with NumPy and matplotlib.

The iq files must be complex float or interleaved unsigned 8-bit.


MIT. See LICENCE for details.


Improve the sync code, to make sure we align the pictures each time. Align on the strongest peak instead of the NULL symbol.

Generate long-term visualisations, to see if there is a change over several days.

Oversample 2x or 4x to get finer time resolution.

Make sure rtl_tcp quits properly on ctrl-c.