[Lowfer] WSPR noise bandwidth, was 74.5495 QRSS 60 as usual ...

[jrusgrove at comcast.net]

>If the software doesn't even LOOK for signals to decode outside its primary 200 Hz analysis 
>band--as WSPR doesn't--then anything else outside that band, be it random or coherent, makes no 
>difference to the decoding.

Not true. The noise is analyzed in a bandwidth wider than 200 Hz - this has been well known since 
the early days of WSPR. You can prove this to yourself by receiving a stable signal during daylight 
conditions starting in an SSB bandwidth noting the received SNR. Change to a cw filter (wider than 
200 Hz) and watch the reported SNR change.

Again, I refer you to the WSPR User Guide:

"Signal levels reported for each WSPR decode are the measured ratio of signal power to average noise
power, scaled to a reference bandwidth of 2500 Hz."

You are free to un-scale the measurements if you prefer it that way.

In your system one would have a table of the various modes, their associated detection bandwidth and 
their required SNR for detection with all modes showing 0 dB +/- a couple dB. To gauge their 
effective weak signal performance, one to another, one would then have to scale them to a common 
reference bandwidth for comparison. Gee ... Joe has already done that for us.

AFAIK you are the only person regularly dissing the SNR system. Since you appear firmly 'wrapped 
around the axle' on this I will exit stage left now.

All the best ... hope you decide to give the digital modes a try some day.

Jay


p.s. Just to clear up an earlier assertion, WOLF and OPERA Deep Search (and maybe others) are 
capable of decoding signals with nothing showing on a QRSS60 screen.








----- Original Message ----- 
From: "JD" <listread at lwca.org>
To: "Discussion of the Lowfer (US, European, &amp;UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Thursday, October 10, 2013 12:51 AM
Subject: Re: [Lowfer] WSPR noise bandwidth, was 74.5495 QRSS 60 as usual ...


> Jay, I know what the manual says... I've been reading it and the WJST manual and others, long 
> before I started messing with WSPR myself.  But simply stating an arbitrary number in a document 
> doesn't explain the point of decreeing a noise bandwidth that's unrelated to channel bandwidth. 
> That's not and never has been standard engineering practice.  As I say, any agreed mutually 
> bandwidth may be fine for *threshold* comparisons, but that is simply not the same thing as 
> signal-to-noise ratio.
>
> Comparing one mode to another with an arbitrarily wide noise bandwidth also has no basis in 
> information theory, where S/N is _defined_ with the same noise bandwidth as the transmission 
> channel necessary for the specific signal.  Without the same bandwidth for the noise as signal, 
> you're not exploring theoretical SNR limits at all...first, because that's not how SNR is 
> measured, and second, because you're inflating the real number by an amount that is going to vary 
> with both (a) the necessary communication bandwidth for a given mode relative to others, and (b) 
> where in the noise passband other non-random signals may fall.  Just a broad illustration of the 
> latter:  If the software doesn't even LOOK for signals to decode outside its primary 200 Hz 
> analysis band--as WSPR doesn't--then anything else outside that band, be it random or coherent, 
> makes no difference to the decoding.  So, why should the other 2300 Hz be counted as noise and 
> allowed to affect the supposed SNR?  That doesn't provide a common basis for measuring detection 
> efficiency at all.
>
> The standard definition of S/N matters for the same reason the "m" in dBm does.  If a person 
> starts using "dBm"  when he merely means a ratio in dB, or uses it to indicate power referenced to 
> something other than 1 milliwatt, then it loses its usefulness.
>
> 73
> John
>
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