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Adding support for new receiver hardware
You can easily add support for other receiver hardware, if it has a commandline tool that can output I/Q samples to the standard output.
If your receiver hardware is not supported yet, you will definitely need to edit config_webrx.py
. Take a look at these lines:
start_rtl_command="rtl_sdr -s {samp_rate} -f {center_freq} -p {ppm} -".format(rf_gain=rf_gain, center_freq=center_freq, samp_rate=samp_rate, ppm=ppm)
format_conversion="csdr convert_u8_f"
Notice that the command to be run by OpenWebRX is something like:
rtl_sdr (...) -
The rtl_sdr
tool is called with various commandline parameters, which are substituted from other settings (like center frequency, sampling rate, PPM). Then the -
at the end says that rtl_sdr
should output the samples to the standard output instead of a file.
There is another important setting: format_conversion
will tell OpenWebRX that the RTL-SDR outputs 8-bit unsigned samples. We have to convert these to 32-bit floating point samples in order to process them with csdr
. The available conversion options are listed on the csdr project page. As a quick reference, you can use:
-
csdr convert_s16_f
for receivers that output signed 16-bit integer data type (AFEDRI SDR, Softrock, etc.), -
csdr convert_s8_f
for receivers that output signed 8-bit integer data type (HackRF).
(To understand how and where does data go within OpenWebRX, and how does it further utilize OS pipes and FIFOs, there is a graph in the thesis paper.)
You can confirm that your receiver's commandline tool works like this:
rtl_sdr - | xxd
It works if you see a bunch of hexadecimal data:
0009c50: c0a6 a71d 48a3 b711 ac24 4a3e dcbd e951 ....H....$J>...Q
0009c60: 83df 7498 24da 37e9 34e1 8f24 da82 a80f ..t.$.7.4..$....
0009c70: 5538 b926 cefe b76e 9609 4e01 451a 01fc U8.&...n..N.E...
...and it doesn't work if you do not see anything.
...to set receiver parameters correctly. Let's say, you own a brand new product called WhateverSDR, which outputs 16-bit I/Q samples at a fixed rate of 200000 sps, from the 2-meter band (145 MHz). It has a commandline tool called whatever_sdr
, but it doesn't let you set the sampling rate from the command line. Then you would do this:
start_rtl_command="whatever_sdr -"
format_conversion="csdr convert_s16_f"
Still you have to set the samp_rate = 200000
and center_freq = 145000000
in config_webrx.py
, so that OpenWebRX would know what to write on the frequency scale, and what to expect while processing the I/Q data.