Re: LF: More 8.97kHz WSPR decodes - changed PC here

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

First calculate S/N alone :

WSPR has a signalling bandwidth of 1.46Hz which is the value to use for noise level calculation.   

QRSS600 has a bandwidth of 0.0017Hz.  They both rely on non-coherent power detection, so assume equal detection sensitivity.

On S/N alone QRSS600 is therefore 10.LOG(1.46/.0017)  =  29dB better than WSPR.

 

BUT.

Soft decision decoding and error correction in WSPR allows perfect copy at S/N of about 4dB in 1.46Hz (== -28dB in 2500Hz for comparison).

QRSS needs about 10 - 12dB, so in terms of coding efficiency, QRSS is 7dB worse.

 

Combining the two gives a total sensitivity imprevement of 29 - 7 = 22dB for QRSS600 over WSPR

Of course, if time of transmission needs to be taken into account the rules change completely........

 

Andy    G4JNT

 

On 27 April 2011 21:45, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:

Dear Eddie (et al)

In the context of the very very weak signals experienced at VLF I don't think WSPR is a serious contender except for localised tests. No doubt someone here far more knowledgeable than me can tell us the "dB advantage" of say, QRSS600 or 6000 versus WSPR, but the difference must be enormous.

Where WSPR scores, in my view, is the automatic reporting via the internet database. This has proved a real boon at 137 and 500kHz. Even here though very slow QRSS would beat WSPR every time.  I am a great believer in WSPR, but do not believe it will be that much use at VLF.

Andy (G4JNT) are you able to comment on please?

73s
Roger G3XBM

On 27 April 2011 20:51, qrss <qrss@talktalk.net> wrote:

Just a further thought. WSPR doesn't of course spread its power over 6Hz it actually transmits full carrier on each of the four frequencies for 0.682 mS and sometimes several of the same element follow without a break in carrier, which accounts for some of the bright spots and lines we see when things are marginal. One element is a longer dot time than 2WPM Morse, and that is SLOW Morse.
Long integration times are out of course.

73 Eddie G3ZJO
 

On 27/04/2011 18:58, Roger Lapthorn wrote:

Hi Eddie (et al)

It is highly unlikely you'd copy Andrew on VLF remembering that the WSPR signal spreads around 6Hz in the transmission burst, so the energy in any narrow FFT bin would be tiny. Also, this is earth mode (I hope, as G6ALB does not hold an NoV to radiate at VLF), so signals are propagating through the ground by conduction and no significant amount of signal is radiated.

I'm still intrigued why the best reception here today was with my 80sq m vertical loop. This outperformed several earth electrode set-ups here at the RX end, an E-field probe and a 30t loop laying close to copper pipe work in the house!  If the signals are coming down the pipes then why don't these more direct means of coupling to them work as well as (or better than) a vertical loop outside? Odd.

73s
Roger G3XBM

On 27 April 2011 18:33, qrss <qrss@talktalk.net> wrote:

Great stuff Roger and Andrew

If you are RX'ing on an 80m dipole it may be worth a look here, I would never say can't until I have tried. Bearing in mind I should be able to observe signals which would not be decode able on WSPR

I would appreciate a prior notification of times and exact frequency of the WSPR signal of any further tests.

Keep it up.

73 Eddie G3ZJO

On 27/04/2011 15:19, Roger Lapthorn wrote:

As an experiment I changed over to my wife's laptop and got immediate decodes of G6ALB's VLF earth mode signal (3km) at -17dB S/N, suggesting the issue with lack of decodes may be with my soundcard and not Andrew's.

1408 -17 -0.6   0.008986  0 G6ALB JO02 47
1410 -17 -0.6   0.008986  0 G6ALB JO02 47
1412 -17 -1.2   0.008986  0 G6ALB JO02 47
1414 -17 -0.8   0.008986  0 G6ALB JO02 47
1416 -17 -0.8   0.008986  0 G6ALB JO02 47

This is a very solid signal on the 80m square single turn vertical wire loop antenna. Andrew is using 44W to an earth electrode antenna.

73s
Roger G3XBM

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http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
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https://sites.google.com/site/sub9khz/

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http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
https://sites.google.com/site/sub9khz/