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+
+## Radiosonde RS92
+
+Tools for decoding RS92-SGP and RS92-AGP radiosonde signals.
+
+### Files
+
+* `nav_gps_vel.c` - include-file for `rs92gps.c`, `rs92gps_2dfix.c`, `rs92ecc.c`, `rs92agp.c`
+
+* `rs92gps.c` - RS92-SGP decoder (includes `nav_gps_vel.c`)
+
+  #### Compile
+  `gcc rs92gps.c -lm -o rs92gps`
+
+  #### Usage
+  `./rs92gps [options] <file>` <br />
+  * `file`: <br />
+    1.1 `<audio.wav>`: FM-demodulated signal, recorded as wav audio file <br />
+    2.1 `--rawin1 <raw_data>`: raw data file created with option `-r` <br />
+    2.2 `--rawin2 <digitalsondeXX.txt>`: SM raw data
+  * `options`: <br />
+      `-i`: invert signal/polarity <br />
+      `-r`: output raw data <br />
+      `-a <almanacSEM>`: use SEM almanac (GPS satellites, orbital data)
+                         (cf. https://celestrak.com/GPS/almanac/SEM/) <br />
+      `-e <ephemperisRinex>`: use RINEX ephemerides (GPS satellites, orbital data)
+                              (e.g. YYYY=2017: ftp://cddis.gsfc.nasa.gov/gnss/data/daily/2017/brdc/,
+                               brdcDDD0.YYn.Z, YY - year, DDD - day) <br />
+     `-v`: additional data/info <br />
+     `--vel`: output velocity (vH: horizontal, D: direction/heading, vV: vertical) <br />
+     `--crc`: output only frames with valid GPS-CRC <br />
+
+  `./rs92gps -h`: list more options
+
+  #### Examples
+  The rs92-radiosonde transmits pseudorange GPS data and GPS time.
+  To calculate its position, orbital data of the GPS satellites is needed.
+  You can use either almanac data which is less accurate (but can be used +/- 3 days),
+  or rinex ephemerides data (recommended) which is more accurate but should not be
+  older than 2 hours.
+  The recommended sample rate of the FM-demodulated signal is 48 kHz.
+  The GPS-altitude is above ellipsoid (in europe, subtract 40-50m geoid height).
+  * `./rs92gps -r 2015101_14Z.wav > raw.txt`  (raw output into `raw.txt`) <br />
+    `./rs92gps -v -e brdc3050.15n --rawin1 raw.txt`
+  * `./rs92gps -v -e brdc3050.15n 2015101_14Z.wav`
+  * `./rs92gps -v --vel2 -e brdc3050.15n 2015101_14Z.wav | tee log.txt` (console output and into file `log.txt`)
+
+  The FSK-demodulation is kept very simple. If the signal quality is low, a lowpass filter is recommended, e.g.
+  (using `sox`)
+  * `sox 2015101_14Z.wav -t wav - lowpass 2600 2>/dev/null | ./rs92gps -v -e brdc3050.15n`
+
+  You can redirect live audio stream to the decoder via `sox`, e.g.
+  * `sox -t oss /dev/dsp -t wav - lowpass 2600 2>/dev/null | ./rs92gps -v --vel -e brdc3050.15n`
+  * `sox -t oss /dev/dsp -t wav - lowpass 2600 2>/dev/null | stdbuf -oL ./rs92gps -v --vel2 -e brdc3050.15n | tee log.txt` <br />
+
+  If the signal is inverted
+  (depends on sdr-software and/or audio-card/settings), try option `-i`.
+
+* `rs92gps_2dfix.c` - test decoder for 2d-fix (if only 3 satellites are available). If the position altitude is known/given,
+  a position can be calculated with 3 satellites.
+
+  #### Compile
+  `gcc rs92gps_2dfix.c -lm -o rs92gps_2dfix`
+
+  #### Usage
+  Same as `rs92gps`.
+  Additional option `--2dalt <alt>`: <br />
+    `<alt>` is the (estimated) altitude of the radiosonde in meters above ellipsoid.
+    Default (without `--2dalt <alt>`) is 0m.
+
+
+* `rs92ecc.c` - RS92-SGP decoder with Reed-Solomon error correction (uses fec-lib by KA9Q)
+
+  #### Compile
+  * ka9q-fec (fec-3.0.1): <br />
+      `gcc -c init_rs_char.c` <br />
+      `gcc -c decode_rs_char.c` <br />
+  * `gcc init_rs_char.o decode_rs_char.o rs92ecc.c -lm -o rs92ecc` <br />
+    (includes also `fec.h` from fec-3.0.1)
+
+  #### Usage
+  Same as `rs92gps`.
+  Additional option `--ecc`.
+
+  Will be replaced by Reed-Solom-Decoder in `RS/ecc/bch_ecc.c` (cf. `RS/rs41/rs41ecc.c`).
+
+
+* `rs92agp.c` - RS92-AGP, RS92-BGP decoder
+
+* `rs92.txt` - infos
+
+* `pos2kml.pl`, `pos2gpx.pl`, `pos2nmea.pl` <br />
+  perl scripts for kml-, gpx-, or nmea-output, resp.
+  #### Usage/Example
+  `./rs92ecc --ecc --crc -v --vel2 -e brdc3050.15n 2015101_14Z.wav | ./pos2nmea.pl` <br />
+  `stderr`: frame output <br />
+  `stdout`: NMEA output <br />
+  Only NMEA:
+  `./rs92ecc --ecc --crc -v --vel2 -e brdc3050.15n 2015101_14Z.wav | ./pos2nmea.pl 2>/dev/null`
+
+
+* `gps_navdata.c` - test tool/example, compares orbital data. Includes `nav_gps.c` and
+  compares `almanac.sem.week0843.061440.txt`, `brdc2910.15n`, `nga18670.Z`.
+
+<!-- * `rs92-almanac_gps_outage.jpg` -->
+
+