Re: FT8-Call HF Path Tests

Ev Tupis
 

Hi Tony,

I have to admit that I am not familiar with Contestia to know for sure, however it seems that it is a "real time mode", one that displays what is decoded in "real time".

Given that (possible misunderstanding on my part), the comparison to the computer augmented modes such as the JT-fleet is only loosely possible.

If Contestia's RX was computer augmented during the TX cycle and displayed afterward, I would think that intelligence could be extracted to much lower signal levels...likely rivaling JT-modes.

My hypothesis is based on our previous thread, identifying the "magic of JT" as occurring in computer processing.

However...nobody (to my knowledge) has a computer augmented (post-processed) version of Contestia to know for sure.  Again, kudos to the "JT team" for leveraging the augmented approach.

Kindly,
Ev, W2EV





On Monday, October 1, 2018, 6:32:06 PM EDT, Tony <DXDX@...> wrote:


All:

I've been testing several modes to try and duplicate the the weak signal
performance of FT8 without success. A few existing protocols configured
to decode near -20 s/n (AWGN channel) do not meet the same criteria for
speed, HF channel performance, bandwidth or latency.

One example is Contestia 16/125 which can decode near -18db s/n. The
problem is that it takes a minute before you see the first few
characters due to latency. In contrast, FT8 would have sent 60
characters in the same amount of time and would have been in receive
mode by then.

Once the latency subsides after the initial transmission, the mode is
still only sending 0.6 characters / second or roughly half that of FT8
and that's with 2.5 times the bandwidth.

Discounting latency, slow throughput and bandwidth, this particular mode
does not endure HF path simulations at those low s/n ratios. The result
is having to increase the s/n by 8 to 10db in order to achieve the same
error-free performance: thats an equivalent of up to a 10 fold increase
in power.

I CAN duplicate the performance of FT8 with existing modes like Olivia
or Contestia using 1000 or 2000 Hz bandwidths with very slow (128 tone)
baud rates which have the same latency. If latency could be eliminated
your still left with a mode that's 20 to 40 times the bandwidth of FT8.

So, if anyone has any mode suggestions that might meet the same or
nearly the same criteria as FT8 as described, please pass them along.

Tony -K2MO









> 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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