What SNR do you want to receive?

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DJ6LB
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Joined: 2009/02/01 - 00:45
What SNR do you want to receive?

Hi all,
the title is deliberately a bit provocative. But read on:
Since starting in WSPR I was intrigued about SNR and receiving bandwidth. We all know that the SNR is referenced to 2,5kHz and this is the bw to use.
Knowing that G4JNT in the last days has always appeared on 503,3850kHz between 19:30 and 20:00 UTC at my QTH (and is the only stn there) I waited until I saw traces on that frequ. Then I reduced the bw in my Flex-5000 to 10Hz (+/-5Hz around '850) and waited until decode. The first was at 19:52 with a SNR of +3!!! I waited to another decode: 20:22 with a SNR of +7!!! Then, when I saw traces again at 20:26, right in the middle of the 2min period, I opend the filter up und decoded with a SNR of -21 and at 20:36 & 20:46 with -27 / -28!
What do we learn?
Obviously the software is not tolerant to DRASTICALLY reduced bw. If e.g. you inadvertendly reduce your RX bw, the SNR reports you produce are not meaningful.
By all what I have seen, I cound not decode BETTER by reducing the bw.
These are by no means exhausting tests. The easiest way to do a bit more testing would be, if a stn would transmit continously for some time (like SM6BHZ did a while ago) and we would switch filters between transmissions.

73
de
Klaus
dj6lb