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New Digital Contest Mode: FT4

Alden Oyer
 

"FT4 is an experimental digital mode designed specifically for radio contesting. Like FT8, it uses fixed-length transmissions, structured messages with formats optimized for minimal QSOs, and strong forward error correction. T/R sequences are 6 seconds long, so FT4 is 2.5 × faster than FT8 and about the same
speed as RTTY for radio contesting. FT4 can work with signals 10 dB weaker than  needed for RTTY, while using much less bandwidth."

CHeck out:
http://physics.princeton.edu/pulsar/k1jt/FT4_Protocol.pdf

Enjoy,
Alden Oyer, AG5S 

Keith Morehouse
 

 ..and the WSJT musical chairs performance moves on.

At least THIS "experimental" mode is going to have a timer in it's alpha release that will force it to stop working right before the June VHF contest...

-W9RM


Keith Morehouse
via MotoG


On Mon, Apr 22, 2019, 4:01 PM Alden Oyer <atoyer@...> wrote:
"FT4 is an experimental digital mode designed specifically for radio contesting. Like FT8, it uses fixed-length transmissions, structured messages with formats optimized for minimal QSOs, and strong forward error correction. T/R sequences are 6 seconds long, so FT4 is 2.5 × faster than FT8 and about the same
speed as RTTY for radio contesting. FT4 can work with signals 10 dB weaker than  needed for RTTY, while using much less bandwidth."

CHeck out:
http://physics.princeton.edu/pulsar/k1jt/FT4_Protocol.pdf

Enjoy,
Alden Oyer, AG5S 

Mike WB2FKO
 

Quite an interesting development!

The whitepaper shows that Gaussian Frequency Shift Keying dramatically reduces the modulation bandwidth compared to FSK. This is essential to allow multiple stations to occupy the receiver passband, as is the case with FT8.  The channel bandwidth is about twice that of FT8, but their testing shows up to 50 stations can still reliably use the channel (proposed 50.318 MHz for FT4 on 6m).  It would be interesting to learn how much sensitivity is lost (how many dB?) by using GFSK compared to FSK.  Note that GFSK is an established modulation scheme:


They tested the possibility of running FT4 asynchronously, but it seems this leads to excessive channel congestion.  I suspect the Costas Arrays must still be in there to get the FEC to work.  If so, my hunch is that shorter sequences will make Internet synchronization of computers more demanding (tighter) than FT8.  I will have a look at the source code when it is made available next Monday (29 April).

WSJT-X is an open source project, but it's pretty clear that protocol development was done by private communication among a select few.  Given the large amount of noise on the WSJT mailing lists, I would have done the same for the sake of minimizing needless distraction.

FT8 and FT4 are clearly incompatible, which is why there will be separate frequencies on each band.  Will FT4 be used by 6m operators instead of SSB when the band really opens up, even in non-contest conditions?  Will it displace FT8 just as FT8 displaced JT65?

-WB2FKO

On 4/22/19 4:01 PM, Alden Oyer wrote:
"FT4 is an experimental digital mode designed specifically for radio contesting. Like FT8, it uses fixed-length transmissions, structured messages with formats optimized for minimal QSOs, and strong forward error correction. T/R sequences are 6 seconds long, so FT4 is 2.5 × faster than FT8 and about the same
speed as RTTY for radio contesting. FT4 can work with signals 10 dB weaker than  needed for RTTY, while using much less bandwidth."

CHeck out:
http://physics.princeton.edu/pulsar/k1jt/FT4_Protocol.pdf

Enjoy,
Alden Oyer, AG5S