[ADXA] Joe Taylor's explanation of "FT2"

[WB5JJJ]

The name FT2 was first used for a ham radio digi-mode in January 2019, when
Steve Franke (K9AN), Bill Somerville (G4WJS), and I were exploring possible
digital modes that might plausibly become popular for ham radio contesting.
In addition to timed-sequence modes like
speeded-up versions of FT8, we considered asynchronous modes similar to
traditional RTTY, but offering far lower error rates and much better
weak-signal performance.

We implemented test protocols of both synchronous and asynchronous types,
using different original codecs and digital modulation ranging from 2-tone
minimum shift keying (MSK) to 4-tone Gaussian-shaped frequency shift keying
(4-GFSK). We tested these modes on the air with a range of speeds,
including full transmissions as short as 2.5 s conveying two callsigns plus
a grid locator, signal report, or contest exchange. We explored the loss of
effective throughput of each experimental mode on a wide range of simulated
ionospheric propagation channels.

With the help of a number of contest-oriented beta testers, we arranged
mock-contest practice sessions, testing one asynchronous mode and several
synchronous modes with different T/R cycle lengths. The testing group's
overall judgment was that timed-sequence modes faster than 7.5 s do not
leave enough time for operator judgment and interaction. They necessarily
require levels of automation that obviate the desirable contesting emphasis
on operating skill and making good strategic decisions. In June 2019 we
settled on the protocol specification that became FT4. It was released as
part of WSJT-X 2.1.0 on July 15, 2019. I consider FT4 to be a moderately
successful mode, but even for contesting it has not replaced (or even
caught up to) FT8 in popularity.

Despite what you may have read (e.g., "This innovative protocol was
developed from scratch by Martino (IU8LMC) and the ARI Caserta Team"), the
mode recently being called "FT2" is nothing more than FT4 sent at twice the
speed. Indeed, the "FT2" offered by DG2YCB in an experimental "WSJT-X i+"
version uses the exact FT4 software and simply scales the generated and
received waveforms by a factor of 2.

Compared with FT4, "FT2" is significantly less sensitive, needs twice the
bandwidth, and has far more decoding failures caused by timing errors. The
mode is hardly usable without full (or nearly full) automation. We have no
plan to add a twice-speeded-up version of FT4 in the mainline program
WSJT-X. We are, however, experimenting with a possible asynchronous mode
that would be operationally more like traditional RTTY. It's too soon to
say when (or if) it might be released for wider testing.

-----

73's
George - WB5JJJ
HoIP - 100105
Cell - 479.857.7737
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