Re: FT8-Call HF Path Tests

Ev Tupis
 

Very interesting!  As I reflect on this, I wonder if these results are because of the modulation, the protocol or the demodulation-strategy (or a little of each).

"Would PSK31 (or any other) modulation" deliver similar result if the payload were structured the same and be post-processed prior to display?

"Where does the magic happen?"

Ev, W2EV


On Saturday, September 22, 2018, 9:19:18 PM EDT, Tony <DXDX@...> wrote:


All:

I spent some time testing FT-8 Call to see how well it does in the
noise. I found that it's certainly capable of error-free decodes down to
-22db s/n (3KHz b/w) on AWGN channels. See FT8AWGN screenshot.

It did require better s/n ratios when subjected to multi-path
simulations (common with any mode when s/n ratios are near the decode
threshold) but still managed -18db s/n, error-free decodes. See FT8MP
screenshot.

I also did some weak signal tests on the 40 meter band between New York
and New Zealand. Multi-path is inevitable on such a long path, but the
mode produced fairly consistent decodes down to -23db s/n. See: ZLNY
screenshots 1,2 and 3.

The New Zealand station (ZL2AUB) was running 20 watts to a dipole at 30
feet while I was using 10 watts with a rotatable dipole at 75 feet. I
kept reducing power to get the reports down into the -20db range.

I may be wrong, but I don't believe there's another chat-mode protocol
that can duplicate this type of weak signal performance on HF. Not at
that bandwidth and at that speed. Or is there?

Tony -K2MO







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