APRS with rtl_fm, direwolf, and multimon-ng / and also airspyhf_rx

APRS-airspyhf_rx.md

APRS with airspyhf_rx, csdr, and direwolf

1200bps 144.660MHz

# Choose 11025Hz for the intermediate IF/audio frequency
airspyhf_rx -f 144.66 -a 768000 -r stdout | \
  csdr fir_decimate_cc 69.65986394557823129252 0.005 HAMMING | \
  csdr fmdemod_quadri_cf | csdr limit_ff 0.5 | csdr deemphasis_nfm_ff 11025 | \
  csdr fastagc_ff | csdr limit_ff 0.5 | csdr convert_f_s16 | \
  /usr/local/bin/direwolf -c ~/bin/sdr-1200bps.conf -t 0 -T "%FT%TZ" -r 11025 -D 1 -B 1200 -

APRS-direwolf.md

APRS with rtl_fm and direwolf

9600bps 144.640MHz

rtl_fm -M fm -f 144.64M -p 36 -s 48000 -g 42 - | /usr/local/bin/direwolf -c sdr-9600bps.conf -r 48000 -D 1 -B 9600 -

1200bps 144.660MHz

rtl_fm -M fm -f 144.66M -p 36 -s 24000 -g 42 - | /usr/local/bin/direwolf -c sdr-1200bps.conf -r 24000 -D 1 -B 1200 -

APRS-rtl_fm-multimon-ng.md

APRS with rtl_fm and multimon-ng

for 144.64MHz 9600GMSK

# number after -p: freq offset (+36ppm) <- this is critical for detecting signals
rtl_fm -f 144.640M -s 22050 -p 36 -g 42 -l 10 - | ./multimon-ng -t raw -A -s AFSK1200 -a FSK9600 -

Addendum: FM radio (NHK-FM Osaka 88.1MHz)

# rtl_fm -f 88.1M -M fm -s 170k -A fast -r 32k -p 36 -g 20 -l 0 -E deemp | play -r 32k -t raw -e s -b 16 -c 1 -V1 -

Sources

• Raspberry Pi + SDR dongle = APRS iGate
• Rtl_fm Guide
• multimon-ng

[End of memorandum]

sdr-1200bps.conf

ACHANNELS 1
ADEVICE null null
CHANNEL 0

MYCALL CALLSIGN
IGLOGIN CALLSIGN ACCESS_CODE
IGSERVER [region].aprs2.net

MODEM 1200

AGWPORT 8000
KISSPORT 8001

PBEACON sendto=IG delay=0:30 every=30:00 symbol="igate" overlay=R lat=xxx long=yyy alt=in_meter comment="144.660MHz Receive-only gateway AFSK 1200bps"

IGTXLIMIT 6 10

sdr-9600bps.conf

ACHANNELS 1
ADEVICE null null
CHANNEL 0

MYCALL CALLSIGN
IGLOGIN CALLSIGN ACCESS_CODE
IGSERVER [region].aprs2.net

MODEM 9600

AGWPORT 8000
KISSPORT 8001

PBEACON sendto=IG delay=0:30 every=30:00 symbol="igate" overlay=R lat=xxx long=yyy alt=in_meter comment="144.640MHz Receive-only gateway GMSK 9600bps"

IGTXLIMIT 6 10