Hi EbNaut
I have been playing again with EbNaut trying to decode Stefan's transmission in 17470Hz
Of course I couldn't remember all the tricks and configurations needed to setup SL and then to extract
the files for the decoder, etc. Had to find the notes I used last time (and first time I decoded Stefan)
Even with that I had no success decoding. May be there is my mistake or maybe there is too much
noise to decode :(
Anyway I thought it would be interesting to resume it in a kind of guide to help others to try. And at the
same time use it as guide for myself in a next try. I have included links to Dropbox because files
attached to the message will not be distributed by the reflector, at least that happens to me
SL must be configured to export FFT files. You also need the EbNaut utilities from Markus, DF6NM
http://df6nm.bplaced.net/VLF/fec_tests/df6nm_ebnaut_utilities.zip
There is a text file "sr.txt" you need to configure according to your SpectrumLab settings this way
The File Export configuration in SL is also very important. The configuration shown will export the files
to a \data4h folder you must create in the main \Spectrum folder were SL is installed
https://www.dropbox.com/s/j9le8em2ac89sis/File%20Export%20configuration.bmp?dl=0
The exported files must be converted to .wav files using Markus application ebnaut_ifft3a.exe
The configuration file sr.txt must be edited and must match SL settings
To convert a file just drag it over the ebnaut_ifft3a aplication and drop. It will produce another file
with same name but .wav format
Then start EbNaut decoder ebnaut-rx and configure all the settings according to the transmission
announce. Assuming the central frequency in SL is the same as transmission frequency there is no
need to configure "Freq.offset" in EbNaut. Our main problem is timing and you need to choose
the right file starting just BEFORE the announced transmission and even then specify the exact
"Start offset" in seconds
I selected a file which should contain Stefan's transmission from last march 16th at 23:30 utc
You will see there is a shift between windows file date stamp and real file start. Fortunately this
is constant and you will be not dummy enought not to figure out which file to choose. If not
the old trial and error will do for your
Select the file in the EbNaut decoder and press Run. You will get the real File start at 23:22:41.040
Then you need to calculate and set the exact Start offset in EbNaut decoder
A clock calculator like this is a good help http://www.calculator.net/time-calculator.html
Anyway you will need to convert the result to seconds. Easy, even for a dummy
Don't forget to increase the CPU number if you are using a multi core processor. Press Run again
and let the force be with you while the decoder work digging for a signal in that file
Sure I'm missing something here. I think have read there is a 4 sample delay to be added to the offset
time. List lenght is also important, but as a dummy I prefer not to place a finger there at this moment
Please elaborate and describe how one (dummy) can translate that to seconds
There is also a lack of lower level explanations about SL here. You must be running sample rate compensation
from 1pps GPS signal, and the system timing must be accurately set. There is also a relation between FFT
configuration and file lenght which determines how much transmission time you get in a single file. Depending
on announced transmission duration it should be modified to fit a complete transmission window
So, please go ahead and feel free to complete this basic instructions. And specially ... CORRECT it !
But always keeping it simple, for us, dummies ;-)
73 de Luis
EA5DOM
