LF: Re: Opera v qrs evaluation

["James Moritz" <james.moritz@btopenworld.com>]

Dear Eddie, LF Group,

> Was -31dB the limit of decoding for OPERA, ie could you take QRS3 to below 
> copy ability yet get decodes from OPERA even if not 100% of the time.
Overnight, your signal decoded 100% of the time with reported levels down 
to -32dB SNR, which seems consistent with G0NBD's -34dB minimum figure. This 
was intended just as a quick "sanity check"experiment - the off-air signal 
and noise levels are not usually stable enough to get better than a couple 
of dBs repeatability, so trying to locate the exact threshold at which Opera 
fails to decode would be long-winded. Rik ON7YD's approach will give more 
precise results.
But for a realistic simulation, some way of including the effects of QSB is 
important too, I think, especially for 500kHz modes intended for 
intermediate to long distances. This is certainly done with HF channel 
simulations when evaluating different modes. I expect modes such as Opera 
and WSPR are rather effective with the frequent deep fades that occur on 
500k, because of their FEC ability to decode correctly when a fairly large 
fraction of the transmitted symbols are lost in a fade. This is certainly a 
problem with using QRSS on this band.
> I am still searching for the reason for never a report on my QRS3
I guess there just isn't a large crowd of people listening on 500k, and you 
would have to be a very conscientious listener to report every signal every 
time, without being specifically requested to do so. That is certainly a big 
benefit of the automated reporting possible with Opera and WSPR. It may not 
give you the "Man Triumphant over the Aether" feeling after spending several 
hours in a shed with headphones clamped to your ears, but it is nice to know 
your PC is reporting every detectable signal while you are at work or tucked 
up in a nice warm bed ;-)
Cheers, Jim Moritz
73 de M0BMU