Dear Jim, Rik, Laurence
Thanks for the information, it does seem from all tests that QRS3 and
OP4 are about equivalent.
QRS as we know takes a human to notice its there among noise and can get
missed. With OPERA (and WSPR) if there is an RX on in range it's de-coded.
73 Eddie G3ZJO
On 31/01/2012 22:51, James Moritz wrote:
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
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