pirip/README.md

Pi Radio IP

Minimal hardware IP over VHF/UHF Radio using RpiTx and RTLSDRs [1].

Project Plan and Status

Next step is to try some Over The Air (OTA) tests.

Milestone	Description
M1	Proof of Concept Physical Layer
M2	Git repo for project, integrated tx and rx applications
M3	Simple GUI Dashboard that can be used to tune and debug link
M4	first OTA tests using uncoded modem
M5	Pi running Tx and Rx
M6	Add LDPC FEC to waveform
M7	Bidirectional half duplex Tx/Rx on single Pi
M8	TAP/TUN integration and demo IP link
M9	Document how to build simple wire antennas

Building

This procedure builds everything locally, so won't interfere with any installed versions of the same software.

RpiTx Transmitter

ssh into your Pi, then:

$ git clone https://github.com/drowe67/pirip.git
$ cd pirip
$ ./build_codec2.sh
$ ./build_rpitx.sh
$ cd tx && make

RTLSDR Receiver

On your laptop/PC:

$ sudo apt update
$ sudo apt install libusb-1.0-0-dev git cmake
$ ./build_codec2.sh
$ ./build_rtlsdr.sh

Testing

1. Transmit two tone test signal for Pi:

   pi@raspberrypi:~/pirip/tx $ sudo ./fsk_rpitx -t /dev/null
   

2. Transmit test frames from Pi for 60 seconds:

   pi@raspberrypi:~/pirip/tx $ ../codec2/build_linux/src/fsk_get_test_bits - 600000 | sudo ./fsk_rpitx -
   

3. Receive test frames on x86 laptop for 5 seconds (vanilla rtl_sdr):

   ~/pirip$ Fs=240000; rtl-sdr-blog/build_rtlsdr/src/rtl_sdr -g 49 -s $Fs -f 144490000 - | codec2/build_linux/src/fsk_demod --fsk_lower 500 --fsk_upper 25000 -d -p 24 2 240000 10000 - - | codec2/build_linux/src/fsk_put_test_bits -
   
   

4. Receive test frames on x86 laptop for 5 seconds (vanilla rtl_sdr at Fs=1.8MHz):

Fs=1800000; ./src/rtl_sdr -g 49 -s $Fs -f 144500000 - | csdr convert_u8_f | csdr fir_decimate_cc 45 | csdr convert_f_s16 | ../../codec2/build_linux/src/fsk_demod --fsk_lower 500 -c 2 40000 1000 - - | ../../codec2/build_linux/src/fsk_put_test_bits -

1. Receive test frames on x86 laptop for 5 seconds (integrated rtl_fsk):

   ~/pirip$  Fs=240000; tsecs=5; ./rtl-sdr-blog/build_rtlsdr/src/rtl_fsk -g 49 -f 144490000 - -n $(($Fs*$tsecs)) | codec2/build_linux/src/fsk_put_test_bits -
   

   Note this is tuned about 10kHz low, to put the two tones above the rtl_sdr DC line.

2. Demod GUI Dashboard. Open a new console and start demod_gui.py:

   ~/pirip$ netcat -luk 8001 | ./src/dash.py
   

   In another console start the FSK demod:

   ~/pirip$ Fs=240000; tsecs=20; ./rtl-sdr-blog/build_rtlsdr/src/rtl_fsk -g 1 -f 144490000 - -n $(($Fs*$tsecs)) -u localhost | codec2/build_linux/src/fsk_put_test_bits -
   

   

3. Automated loopback tests. Connect your Pi to your RTLSDR via a 60dB attenuator

   Using vanilla rtl_sdr:

   ./test/loopback_rtl_sdr.sh
   

   Using integrated rtl_fsk:

   ./test/loopback_rtl_fsk.sh
   

   You can monitor loopback_rtl_fsk.sh using dash.py as above.

4. Using a HackRF as a transmitter, useful for bench testing the link. The relatively low levels out of the HackRF make MDS testing easier compared to attenuating the somewhat stronger signal from the Pi. This example generates 1000 bit/s FSK with a 2000Hz shift:

   cd codec2/build_linux/src
   ./fsk_get_test_bits - 60000 | ./fsk_mod -c -a 32767 2 40000 1000 1000 2000 - - | ../misc/tlininterp - t.iq8 100 -d -f
   

   The output samples are at a sample rate of 4MHz, and a frequency offset of +1 MHz. They can be played out of the HackRF with:

   hackrf_transfer -t t.iq8 -s 4E6 -f 143.5E6
   

   The signal will be centred on 144.5 MHz (143.5 + 1 MHz offset).

Reading Further

1. Open IP over VHF/UHF - Blog post introducing this project
2. Previous Codec 2 PR discussing this project
3. Codec 2 FSK Modem
4. RpiTx - Radio transmitter software for Raspberry Pis
5. rtlsdr driver - Modified Osmocom drivers with enhancements for RTL-SDR Blog V3 units.