Re: LF: WSPR or QRSS: which is better?

[Andy Talbot <andy.g4jnt@gmail.com>]

You can only fill in the gaps if you know what you're expecting.

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KEV turns into a sort-of  VTM   with a few dot symbols in error

 

(view using a fixed width font)

 

DFCW would be a far better solutino

 

'jnt

         

On 24 August 2011 17:26, mal hamilton <g3kevmal@talktalk.net> wrote:

Like the man says either you get something or NOTHING which is often the case, whereas with QRS you always get SOMETHING and since all radio amateurs are competent with morse code and where

 there is fade or drop out you can fill the gaps, not the case with wspr or the other data modes, and like I said already with poor un decodeable wspr had the transmission been in QRS a messages could be exchanged.

g3kev

 

 

----- Original Message -----

From: Andy Talbot

To: rsgb_lf_group@blacksheep.org

Sent: Wednesday, August 24, 2011 5:12 PM

Subject: Re: LF: WSPR or QRSS: which is better?

WSPR works in a 1.46Hz signal bandwidth and because of its very high level of error correction and soft-decision decoding, means that it will work at a S/N of about 3dB in this bandwidth, and sometimes a bit lower still  (Normally, FSK with no correction at all needs about 10 - 12dB S/N for near error-free performance)

 

QRSS has to show about 6 - 10dB in its signal bandwidth to be able to discern fully what is sent, although a slightly lower S/N may be useable when you 'know' what you should be receiving.  (A form of forward error correction is now in use here as well perhaps :-)  So lets say 5dB S/N is a working value..

 

So take 3dB in 1.46Hz as a starting point and derive the bandwidth for QRSS needed to get 5dB S/N with the same signal.  This will have to be narrower to get a 2dB higher S/N and works out as 1.46 / 10^(2/10) = 0.92Hz

 

So QRSS used with a 0.9Hz bandwidth - which I think means about a 2 - 3s dot period ought to be decoded at the same S/N as a WSPR signal.   Which is probably the info you wanted.

 

But now compare source coding efficiencies.   WSPR fits a callsign, locator and power level into a 110 second transmission - and gives absolutely guaranteed error free decoding, or nothing at all.  About 12 characters in actuality, but that is being a bit unfair as the coding forces certain callsign and locator formatting.   So in all probablility, more like 7 or 8 effective characters (I'm being a bit empirical here)

 

Assuming standard QRSS - not DFCW - , which if like standard Morse, then 5 characters takes about 50 dot symbols to send (12WPM = 60 chars in 1 minute, = 1 char / second, or about 10 dot periods / second.    Dot speed = WPM / 1.2)   If we have 2s dots, that is 5 characters can be sent in the time for a WSPR transmission.

 

So as a quick estimate, WSPR wins by roughly 2dB in S/N terms for a given dot period / noise bandwidth.  And at similar S/N values, WSPR is about 1.5 times faster

Andy

www.g4jnt.com

 

 

 

 

On 24 August 2011 16:42, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:

A question for the coding experts here: WSPR is an excellent weak signal beaconing mode, but at what QRSS speed is QRSS "better" ?

73s
Roger G3XBM

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