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LF: Re: Opera v qrs evaluation

To: <[email protected]>
Subject: LF: Re: Opera v qrs evaluation
From: "James Moritz" <[email protected]>
Date: Tue, 31 Jan 2012 22:51:21 -0000
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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

Attachment: G3ZJO_qrss_op.jpg
Description: JPEG image

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