Mixed uncoded and FEC telemetry reception (December 2003)

Phil Karn has changed his code and split dpsk_demod into two parts, dpsk_demod and fec_decode, and provided in addition p3_convert for converting the 256 byte blocks from fec_decode into the usual 512 byte blocks. The following refers to ao40prototype-5.01 (July 2003).

In order to use fec_decode and p3_decode with the same data stream, two pipes have been installed (as hidden files: .telem.1 and .telem.2). And for merging the decoded blocks in proper sequence, "fflush(stdout)" instructions have been added in p3_convert and p3_decode after fwrite(...,stdout). Otherwise the output comes in 4096 byte junks (8 telemetry blocks).

Four processes are started. The first one reads from the sound card and starts dpsk_demod, feeding the two pipes. The next two processes invoke the two decoders.The fourth process deletes with a filter (tlmuniq) duplicate A blocks, in cases were the same block is received in uncoded and FEcoded form, and feeds a display program (phase3d) in parallel to the output file.

rec -c 1 -r 9600 -s w -f s -t raw - | dpsk_demod --verbose | tee .telem.1 .telem.2 > /dev/null

cat .telem.1 | p3_decode --verbose >> Tyymmdd.raw

cat .telem.2 | fec_decode --verbose | p3_convert >> Tyymmdd.raw

tail -c 512 -f Tyymmdd.raw | tlmuniq | tee -a Tyymmdd.tlm | phase3d

Programming set up for FEC telemetry reception test (June 2003)

Test setup: 1.2m dish, G3RUH patch, preamp MKU232,IC-970/UX-98 Hardware modems: DSP-12, G3RUH digital (outputs merged) Sound card with KA9Q's dpsk_demod (ao40prototype-1.2.1)

Reading from devices (DSP-12, G3RUH demod, audio card):

phase3 /dev/ttyC0 2>logDSP12.1194 | etmfilter 0x80 0x00 >> k030607.raw

phase3 /dev/ttyC4 2>logG3RUH.1194 | etmfilter 0x80 0x00 >> k030607.raw

rec -c 1 -r 9600 -s w -f s -t raw - | dpsk_demod --verbose >> demodout.1194 2> logFEC.1194

Process raw data and display data:

tail -c 512 -f k030607.raw | tlmuniq | tee -a k030607.tlm | phase3d

tail -c 256 -f demodout.1194 | fecfilter blockAhead | tee -a f030607.a | phase3d

Display logs:

tail -f logDSP12.1194

tail -f logG3RUH.1194

tail -f logFEC.1194

Postprocessing:

cat k030607.tlm | tlmfilter 0xff 0x41 >> k030607.a
Not necessary, since A blocks only have been transmitted.

Output files for inspection:

You find in files.zip the log files logDSP12.1194, logG3RUH.1194, and logFEC.1194, the dpsk_demod output (256 byte blocks) as demodout.1194, the output converted to normal A-block format (512 byte blocks) in k030607.fec, the A blocks merged from DSP-12 and G3RUH demod (for MA 113 to 243) in k030607.tlm. Finally a summary.1194 file is provided, which shows a prediction listing by MA with squint angle, number of CRC=OK blocks received by the two hardware demods, the number of FEC encoded blocks received by Phil Karn's dpsk_demod, and some error information, extracted -- not quite correctly -- from the logFEC.1194.