[Fwd: LF: long haul QSO's]

[Andre Kesteloot]

Rik Strobbe wrote:

> Hello group,
>
> Recent test on 136kHz and 73kHz have shown that amateur signals can be
> copied over distances up to 6000km (73kHz) or even 13000km (136kHz).
> So far most tests have been done using 'traditional' QRSS or
> a-bit-less-traditional DFCW. These modes have the advantage that they are
> still based on the CW code (and thus easy to read) but their disadvantage
> (especially for QRSS) is the rather inefficient data rate.
> CW code is optimized for copy by ear and transmission of plain text, what
> we want to do is copy by eye (or even machine) and transmittion mainly
> callsign where characters appear pretty random. A basic check on common
> callsign reveals that the average callsign has 1 figure and 4 / 5 letters,
> so one could assume that a QSO between a LLFLL (or LFLLL) ans a LLFLLL
> callsign is average (where L stand for a random letter, F for a random
> figure).
> Going through the alphabet show that the average letter (including
> inter-character spacing) has a length of 11.23 dots in CW (QRSS) and 4.15
> dots in DFCW. The average figure is 17 dots in QRSS and 6 dots in DFCW.
>
> A typical QSO could be (L = random letter, F = random figure) :
> cq LLFLL k
> LLFLL LLFLLL k
> LLL LL mm k
> LL LLL oo sk
> sk
> This QSO would have a length of 519 dots in QRSS and 166 dots in DFCW (eg.
> assuming 60 sec dotlength the QSO would take 8h39m in QRSS and 2h46m in DFCW)
>
> A QSO on sked would be a bit shorter :
> LLFLL LLFLLL k
> LLFLLL LLFLL mm k
> LL LLL oo sk
> sk
> This QSO would take 443 dots (7h23m) in QRSS and 149 dots (2h29m) in DFCW.
>
> If we want to proceed faster we do have to leave the traditional CW code. A
> very interesting suggestion was recently done by Stewart, KK7KA : a 7 tone
> code. This code would allow us to have a set of 49 characters, sufficient
> for our purpose (A-Z, 0-9, / and ? would do).
> Using this code each character would only take 2 dots, meaning that the
> first example (QSO starting with CQ) would only take 94 dots (1h34m at
> 60sec/dot).
> This assumes that a character starts at a known time, so no need for
> inter-character spaces, but at 60 sec/dot or slower this should be no
> problem (eg. using 60 sec/dot any character would always start exactly at
> an even minute).
> Some additional time can be won if we assign special characters for the T,
> M, O in the report and for the K, SK at the end of a transmission. If the
> 'M' of the report or the 'K' at the end cannot be mixed up with a M or T in
> a call we can omit the spaces before and after the report and before the
> K/SK at the end.
> This would speed up things a bit, making the QSO on sked taking 68 dots (or
> 1h08m) long. Remember, in QRSS it would take 7h23m.
>
> The main problem of the 7 tone code would be the frequency calibration at
> the RX side, but using smart coding this could be solved. One way would be
> by assigning a code that contains the highest and lowest frequency to space
> (the most frequent character), this would reveal both the base frequency
> and the frequency shift at least once per transmission.
>
> I am well aware that there will be strong objection against leaving the CW
> code. But there was also a lot of protest against the first QRSS QSO and
> when DFCW was introduced. Meanwhile both systems proved that they were a
> significant improvement in weak signal communication. I believe that moving
> on to a more efficient code is just a mather of the 'state of mind', CW
> code is just a convention and no convention is secret.
>
> Since we now have shown that is technical possible to copy our signals over
> 10000km and more the time might be right to develop a mode that will allow
> us to make QSO's over these distances.
>
> 73, Rik  ON7YD