On 7/3/2018 9:47 AM, Black Michael via wsjt-devel wrote:
That sounds like a jolly good idea....but why only 7dB improvement?
Wouldn't you recover all the loss from 5 slots=-14dB?
No.
With one signal handling 5 QSOs the information payload must be
increased from 72 to nearly 360 bits. The price of having to decode 350
bits rather than 72 bits is the "other" 7 dB = 10log(360/72).
And how about increasing to 600Hz width and 10 slots? Another 2X would
probably be worth it and still stay below 1000 offset.
Nslots is a design parameter; we can set its maximum wherever we choose.
Sensitivity per slot must degrade at least as fast as 1/Nslots, or in dB
-10log(Nslots).
If we stay with 8-FSK and a r=1/2 code, bandwidth must go up at least in
proportion to NSlots.
Just think of how many QSOs they could have done at full power and 10 slots.
Let's not get carried away...
For the few times I saw them only saw 2 slots running.
Most of the time on 30, 20, and 17m they have been using NSlots=3 to 5.
Three slots seems a good choice in many circumstances, and (as we
established during the pre-expedition tests) can yield rates 200/hr or
better.
-- 73, Joe, K1JT
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