Dear all,
I did an atempt to compare Opera with WSPR, QRSS3 and DFCW10.
I did it by generating audiofiles that contain a Opera2, WSPR, QRSS3 and DFCW
signal of identical amplitude (but slightly different frequency and add a known
amount of (white) noise to get a known SNR.
I started from -20dB and then down in 1dB steps, till -33dB. For each SNR level
I generated 5 audiofiles.
All was done by a small application I wrote.
Results:
WSPR:
- 100% (5 out of 5) decodes as low as -29dB SNR.
- 1 out 5 decode at -30dB SNR
- no decodes at lower SNR
- SNR given by WSPR was always within a +/- 1dB range of the calculated SNR
Opera2:
- 100% (5 out of 5) decodes as low as -22dB SNR
- 4 out of 5 decodes at -23dB SNR
- no decodes at lower SNR
- SNR values given by Opera2 differ about 4dB with the calcualted SNR (Opera2
gives -24dB at calculated 20dB ...)
QRSS3 / DFCW10:
Here comes the tricky part. While with the WSPR and Opera software it is simple
to see wether there is a decode or not, this is not the case with QRSS and
DFCW.
For this modes the operator's experience, both for setting the right parameters
in the QRSS software as for reading noisy signal, plays a role.
For that reason random characters were generated. The software used was SpecLab
with the default settings for QRSS3 resp. QRSS10.
I could easily read QRSS3 as low as -24dB SNR and DFCW10 as low as -27dB SNR.
But is is likely that more experienced ops do 1 or 2 dB better.
If there is some interest I am willing to put the screen captures on a website
for those who want give a try in decoding the QRSS / DFCW signals.
Conclusion: I was a bit surprised by the +/- 6dB difference between WSPR and
Opera2.
Both have about the same transission duration. But WSPR transmits more
information (call + 4 digit loactor + power) compared to Opera (only call). So
that should be in the favour of Opera (more redundancy in the FEC).
But Opera seems to use some kind of Manchester coding, so 50% of the bits are
sacrified to synchronisation.
And finaly is WSPR a 100% duty cycle mode versus 50% for Opera, so the average
power in 3dB lower for Opera. So that might be an explanation for the 6dB
difference.
Based on the above Opera2 and QRSS3 seem to be competitive. DFCW10 outperforms
them and WSPR is even a bit better than DFCW10.
But: these result are based on a relative low numer of measurement (5 at each
SNR level) and with artificial white noise. So it certainly is not written in
stone.
73, Rik ON7YD - OR7T
________________________________________
Van: [email protected] [[email protected]]
namens James Moritz [[email protected]]
Verzonden: dinsdag 31 januari 2012 19:35
Aan: [email protected]
Onderwerp: LF: Re: Opera v qrs evaluation
Dear Eddie, LF Group,
In an attempt to actually make a comparison, I have set my RX to the 500kHz
WSPR frequency, with Spec Lab going also. Since it has been running, G3ZJO's
QRSS3 has been about 10 - 15dB SNR in 0.3Hz FFT resolution, so say about 6dB
above the level needed for "good copy". Opera has so far reported SNR
between -23 and -27dB - I don't know how this relates to the detection
threshold for the Op4 mode. I'll leave it going for a while...
Cheers, Jim Moritz
73 de M0BMU
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