Re: LF: WSPR, QRSS, CW...

["mal hamilton" <g3kevmal@talktalk.net>]

Andy

At least my discussion and observations about radio operators versus appliance operators has provoked some further analysis and comments by yourself and others.

The beauty of CW and variations of the mode handled by a competent operator is simplicity, just a basic TX carrier keyed on/off, basic RX just a regen TRF device and a good pair of Ears. The appliance operator needs computers, appropriate software and keyboard skills to try and achieve a similar result, and often fails.

There is no substitute for a skilled radio operator to pass essential short messages, which applies to most radio amateur communications, however if one requires large volume exchanges of messages or data then some mechanical or electronic support is useful as in commercial radio. The machine operator/appliance operator is useful in this case, why pay a skilled radio operaror.

The discerning LF/MF interesred person should start by learning the morse code, build a simple TX/RX, get as much wire into the air as possible(antenna) fire up and surprise yourself with the results pounding the KEY.

G3KEV

 

 

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

From: Andy Talbot

To: rsgb_lf_group@blacksheep.org

Sent: Sunday, January 10, 2010 10:49 PM

Subject: Re: LF: WSPR, QRSS, CW...

There is an absolute limit to signalling efficiency, determined by Shannon in 1948 of -1.64dB S/N (normalised bandwidth)   WSPR/WSJT are within about 3 - 4dB of the limit, so we'll only ever get this improvement to play with.   Of course, we can go narrower and narrower and longer and longer, but there comes a point where the ionospheric path just won't support the signalling any more

 

And that's it.  All that's left is more EIRP, directional Rx antennas, noise cancellation and...

 

For the signal in noise story, see if you can find a copies of :

 

"Communication in the Presence of Noise",  CE Shannon,  Proc.  IRE  (now IEEE)   January 1949 

which is the seminal paper that sets the  -1.64dB S/N limit

  

--- and ---

 

"Poisson, Shannon and the Radio Amateur" ,  JP Costas, Proc IRE, December 1959   which spells it all out in a delightfully readable way

 

Most human modes, morse and QRSS, and Hell all come out at a roughly similar normalised S/N, and machine modes, at the moment roughly 4 - 6dB better than the best humans ops.   As shown, coding could further improve things by another couple of dB.

 

So who's going to be the first with MFSK Turbo coding on LF.  ?

That's real Amateur Radio as far as I'm concerned.  Not faffing about struggling to dig tones out of noise or looking for lines of different coloured dots

Andy
www.g4jnt.com

What will happen if in 2 years the next software will be available with even much better error correction and so on? What, if this software is so good that a QSO to VK will be possible?