LF: Re: Opera v qrs evaluation

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

Dear Eddie, LF Group,

I did a rough and ready comparative test on the "sensitivity" of QRSS3 and 
Op4 using your back-to-back transmissions. For 500kHz reception, broadband 
noise from the broadcast stations just east of here is being nulled out 
using a loop oriented N-S. Rotating the loop out of the null position gives 
a convenient way of adjusting the SNR on Eddie's signal. So I increased the 
noise level until I judged Eddie's QRSS was just fully readable (using 0.3Hz 
FFT resolution), then left everything in the same position for 4 
transmissions, during which signal and noise levels stayed nearly constant 
(see the attachment). Opera reported an SNR of -31dB on Eddie's Op4 signal 
for all the transmissions.
So, from what Graham said, Op4 may have a small margin in SNR with these 
conditions. You could argue about what constitutes "readable" QRSS, but 
there can't be more than a few dB difference between this signal and 
something indecipherable without prior knowledge. It takes 4 minutes to send 
a callsign using Op4; you could increase the dot length perhaps to 4s  and 
transmit most callsigns in 4 minutes, which would gain you about 1.2dB. But 
for practical purposes I think, in this test anyway, the two modes are 
approximately equivalent in their efficiency in sending callsigns.
Cheers, Jim Moritz
73 de M0BMU

G3ZJO_qrss_op.jpg
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