horusdemodlib/start_dual_rtty_4fsk.sh

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#!/usr/bin/env bash
#
# Dual RTTY / Horus Binary Decoder Script
# Intended for use on Horus flights, with the following payload frequencies:
# RTTY: 434.650 MHz - Callsign 'HORUS'
# MFSK: 434.660 MHz - Callsign 'HORUSBINARY'
#
# The SDR is tuned 5 kHz below the RTTY frequency, and the frequency estimators are set across the two frequencies.
# Modem statistics are sent out via a new 'MODEM_STATS' UDP broadcast message every second.
#
# Change directory to the horusdemodlib directory.
# If running as a different user, you will need to change this line
cd /home/pi/horusdemodlib/
# Receive requency, in Hz. This is the frequency the SDR is tuned to.
RXFREQ=434645000
# Where in the passband we expect to find the RTTY signal, in Hz.
# For Horus flights, this is on 434.650 MHz, so with a SDR frequency of 434.645 MHz,
# we expect to find the RTTY signal at approx +5 kHz.
# Note that the signal must be located ABOVE the centre frequency of the receiver.
RTTY_SIGNAL=5000
# Where in the receiver passband we expect to find the Horus Binary (MFSK) signal, in Hz.
# For Horus flights, this is on 434.660 MHz, so with a SDR frequency of 434.645 MHz,
# we expect to find the RTTY signal at approx +15 kHz.
MFSK_SIGNAL=15000
# Frequency estimator bandwidth. The wider the bandwidth, the more drift and frequency error the modem can tolerate,
# but the higher the chance that the modem will lock on to a strong spurious signal.
RXBANDWIDTH=8000
# Receiver Gain. Set this to 0 to use automatic gain control, otherwise if running a
# preamplifier, you may want to experiment with different gain settings to optimize
# your receiver setup.
# You can find what gain range is valid for your RTLSDR by running: rtl_test
GAIN=0
# Bias Tee Enable (1) or Disable (0)
# NOTE: This uses the -T bias-tee option which is only available on recent versions
# of rtl-sdr. Check if your version has this option by running rtl_fm --help and looking
# for it in the option list.
# If not, you may need to uninstall that version, and then compile from source: https://github.com/osmocom/rtl-sdr
BIAS=0
# Receiver PPM offset
PPM=0
# Check that the horus_demod decoder has been compiled.
DECODER=./build/src/horus_demod
if [ -f "$DECODER" ]; then
echo "Found horus_demod."
else
echo "ERROR - $DECODER does not exist - have you compiled it yet?"
exit 1
fi
# Check that bc is available on the system path.
if echo "1+1" | bc > /dev/null; then
echo "Found bc."
else
echo "ERROR - Cannot find bc - Did you install it?"
exit 1
fi
# Use a local venv if it exists
VENV_DIR=venv
if [ -d "$VENV_DIR" ]; then
echo "Entering venv."
source $VENV_DIR/bin/activate
fi
# Calculate the frequency estimator limits
# Note - these are somewhat hard-coded for this dual-RX application.
RTTY_LOWER=$(echo "$RTTY_SIGNAL - $RXBANDWIDTH/2" | bc)
RTTY_UPPER=$(echo "$RTTY_SIGNAL + $RXBANDWIDTH/2" | bc)
RTTY_CENTRE=$(echo "$RXFREQ + $RTTY_SIGNAL" | bc)
MFSK_LOWER=$(echo "$MFSK_SIGNAL - $RXBANDWIDTH/2" | bc)
MFSK_UPPER=$(echo "$MFSK_SIGNAL + $RXBANDWIDTH/2" | bc)
MFSK_CENTRE=$(echo "$RXFREQ + $MFSK_SIGNAL" | bc)
echo "Using SDR Centre Frequency: $RXFREQ Hz."
echo "Using RTTY estimation range: $RTTY_LOWER - $RTTY_UPPER Hz"
echo "Using MFSK estimation range: $MFSK_LOWER - $MFSK_UPPER Hz"
BIAS_SETTING=""
if [ "$BIAS" = "1" ]; then
echo "Enabling Bias Tee."
BIAS_SETTING=" -T"
fi
GAIN_SETTING=""
if [ "$GAIN" = "0" ]; then
echo "Using AGC."
GAIN_SETTING=""
else
echo "Using Manual Gain"
GAIN_SETTING=" -g $GAIN"
fi
STATS_SETTING=""
if [ "$STATS_OUTPUT" = "1" ]; then
echo "Enabling Modem Statistics."
STATS_SETTING=" --stats=100"
fi
# Start the receive chain.
# Note that we now pass in the SDR centre frequency ($RXFREQ) and 'target' signal frequency ($RTTY_CENTRE / $MFSK_CENTRE)
# to enable providing additional metadata to Habitat / Sondehub.
rtl_fm -M raw -F9 -s 48000 -p $PPM $GAIN_SETTING$BIAS_SETTING -f $RXFREQ | tee >($DECODER -q --stats=5 -g -m RTTY --fsk_lower=$RTTY_LOWER --fsk_upper=$RTTY_UPPER - - | python -m horusdemodlib.uploader --rtty --freq_hz $RXFREQ --freq_target_hz $RTTY_CENTRE ) >($DECODER -q --stats=5 -g -m binary --fsk_lower=$MFSK_LOWER --fsk_upper=$MFSK_UPPER - - | python -m horusdemodlib.uploader --freq_hz $RXFREQ --freq_target_hz $MFSK_CENTRE ) > /dev/null