[RTTY] WPX suggestion

[Ktfrog007 at aol.com]

What about variations on a theme, like:
 
W1ABC 599-001 001 W1ABC
W1ABC 599-001 001-001 W1ABC   (used under poor conditions)
 
I've tried these, just to experiment.  Sometimes they seem to work OK,  
while other times they seemed to confuse people.
 
73,
Kermit, AB1J
 
 
In a message dated 2/8/2013 4:45:22 P.M. GMT Standard Time, chen at mac.com  
writes:

On Feb  8, 2013, at 4:19 AM, Bill Turner wrote:

> Please, please, please, NO  dashes. While it does speed up sending, it
> interferes with the USOS  (Un Shift On Space) function which most folks
> agree is a much better  thing to have. USOS greatly reduces requests for
> repeats, especially  when there is QRM and QRN. 


It is another myth that an extra  character helps when you are transmitting 
all numerals.

The extra FIGS  that follows the Space actually hurt.  The reason is this:

if the  probability of the error of a single character is Q, then the 
probability that  you do *not* have to repeat an exchange of N characters (all N 
characters  survives) is (**N is the power of N)

1 - (1-Q)**N

For example,  if Q is 0.1 and N is 8 (e.g., 599-123, i.e. transmitting  
<figs>599<dash>123), then the above probability is 57%.

By  transmitting that extra character, the probability that all characters 
are  received correctly is now

1 - (1-Q)**(N+1)

Or, using the same  probabilities, the probability of not having to repeat 
is now 61%.

The  above with random errors.

Lets see what happens when a dash is  specifically replaced by Space that 
is followed by a FIGS, and we allow  partial reception to count (i.e., the 
other person can still see the 3 digit  that what was sent correctly -- it not 
safe, but I present this in case it is  further argued that a FIGS somehow 
will magically transform a 599-123 into  something readable again).

Recall that the dash can be received  wrongly, but unless it turns into 
LTRS, it will just be printed as some other  FIGS character, e.g., into a dot.  
Recall that a dash is Baudot 0x03 and  a LTRS is a Baudot 0x1F.  The 
Hamming distance is 3.  So the  probability of a dash turning into a LTRS is very 
low.  I.e., if we use  the same Q above of 0.1 (10% of the characters are 
wrong), the probability of  a dash turning into a LTRS is 0.3%.

Lets see what happens when you send  the Space followed by a FIGS.  The 
Space can still get mangled and turn  into something other FIGS character.  But 
lets look at the FIGS that has  to also be sent.  Given the same Q as 
above, that probability that the  FIGS can be turned into a non-FIGS character is 
 9.7%!  When that  happens, you will receive "599 xQWE"  where x is 
anything but a FIGS  character.

What if the space is mangled? well, it is the same as if the  dash is 
mangled... and guess what, you print exactly the same thing as what  dash 
message.  I.e., If the space is mangled into a dot, you copy  599.123, which you 
also copy 599.123 if the dash turned into a dot.   Remember that "123" only 
prints incorrectly for the dash guy when the dash  turns into a LTRS, and the 
receiver prints 599QWE.

The only other  possibility is if the preamble FIGS is received as 
something else (say, as a  dot).

The Space guy is received as ".TOO 123" and the Dash guy is  received as 
".TOO AWE"  Most of us (and some software) will know what  either means, and 
not need a repeated exchange, but a newcomer to RTTY will be  scratching his 
head in both cases, and ask for a repeat.

So, do  yourself a favor.  If the exchange consists of only numerals, use a 
dash  in place of a space.  If the exchanged is mixed, e.g., "599 NH" then  
don't use a dash.  But, don't do it blindly.   Dashes are not  always 
better, but in the case that the original posted presented it (all  numerals) it 
is better. 

73
Chen,  W7AY




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