[RTTY] CQWW exchange

[Kok Chen]

On Sep 30, 2008, at 9/30    9:03 AM, Peter Laws wrote:

> If you receive N5UWY and N9UWY, which is correct?
>
> If you receive N5UWY, N9UWY, and N5UWY, which is correct?
>
> Three is better than two.

I think this too has been discussed in the past.

Odd numbers are good for error correction with no feedback (isn't  
this why there are odd numbers of jurors, Supreme Court justices,  
etc?), but even numbers are sufficient for error detection with a  
high probability of detecting an error, and even numbers can be used  
for error correction with feedback.

a: N5UWY N9UWY (pause)
b: QRZ? (pause)
a: N5UWY N5UWY

is just an example of error correction with feedback.  It is not such  
a bad idea if propagation is good, since you don't execute the last  
two exchanges often.

When you start detecting more repeats, then switching to a series of  
3 calls could take less over all time:

a: N5UWY N9UWY N5UWY (pause)
b: (gotcha!)

IMHO, it might be better to be nimble and have two different macros  
ready.  You can even modify the software to automatically use one of  
the two macros depending on the SNR the demodulator sees.  (But I am  
against automating contests even more -- it takes all the fun and  
challenges out of them.)

73
Chen, W7AY