Re: LF: 8270Hz

[Markus Vester <markusvester@aol.com>]

Hi Paul,

 

when using the SpecLab FFT-export method with very slow samplerates, I noticed that I had to add about four samples worth to the time offset for best decodes (presumably due to some internal pipelining in the software). I tried that on your 1 s/s file. Running the decoder with 61 rather than 60 s offset happened to reduce the number of symbol errors from 388 (0.4 dB) to 369 (1.3 dB Eb/N0).

 

Best 73,
Markus

-----Ursprüngliche Mitteilung----- 
Von: Paul Nicholson <vlf0403@abelian.org>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mo, 14 Mrz 2016 8:08 pm
Betreff: Re: LF: 8270Hz

 

Uwe wrote: 

 

 > can I get somehow your 8270Hz .WAV file from today 

 

I made three WAV files suitable for input to ebnaut-rx 

(the header contains frequency and time info).  All 

files begin 02:59:00 and decode with a start offset 

of 60.00 

 

Various sample rates and file sizes: 

 

  30 samples/sec 2.8 Mbyte Eb/N0 = 1.0 dB 

  http://abelian.org/vlf/tmp/dj8wx_160314_30.wav 

 

  10 samples/sec 936 Kbyte Eb/N0 = 0.6 dB 

  http://abelian.org/vlf/tmp/dj8wx_160314_10.wav 

 

  1 samples/sec 96 Kbyte Eb/N0 = 0.4dB 

  http://abelian.org/vlf/tmp/dj8wx_160314_1.wav 

 

I notice that the error rate increases a little as I reduce the 

bandwidth. Here I usually decode from a rate 240 samples/sec 

and got Eb/N0 = 1.2 dB but it's down to 0.4 dB after resampling 

to the lowest rate.   I'm not sure why that is. 

 

 > the carrier is on. 

 

Amplitude and phase plotted in 5 minute steps 

 

  http://abelian.org/vlf/tmp/160314b.gif 

 

Some pretty wild variations of phase but it 

settles down from about 02:00 onwards.   I tried 

to decode the earlier carrier as an 'all-star' message, 

but without success at symbol length 10 seconds. 

 

-- 

Paul Nicholson 

-- 

 

dj8wx_160314_1-log_61s.txt
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