FT8 en ny digital mode for Es af K1JT

K1JT har lanceret en ny digital mode. Denne gang med fokus på Es udbredelse. QSO hastigheden er sat 4 gange i vejret i forhold til JT65 uden, at det koster ret meget på signal/støj forholdet. Den nye mode hedder FT8 og er en del af wsjt softwaren. Umiddelbart ser det ud som et spring fremad. Man kan dog spørge sig selv om der ikke kan komme for mange digitale modes, ville det være en fordel at bruge FT8 også til tropo forbindelser? Læse mere i Joes release notes nedenfor.

 

Release: WSJT-X Version 1.8.0
—————————–

NEW FEATURES IN WSJT-X Version 1.8.0
————————————

1. New mode called FT8: sensitivity down to -20 dB on the AWGN
channel; QSOs 4 times faster than JT65 or JT9; auto-sequencing
includes an option to respond automatically to first decoded reply
to your CQ.

2. New mode for accurate Frequency Calibration of your radio.

3. Improved performance of decoders for JT65, QRA64, and MSK144.
MSK144 includes facilities for amplitide and phase equalization
and an “SWL” mode for short-format messages.

4. Options to minimize screen space used by Main and Wide Graph
windows.

5. Enhanced management scheme for table of operating frequencies, and
a new set of default frequencies specific to the three IARU
Regions.

6. Improved CAT control for many rigs, including those controlled
through Commander or OmniRig.

7. New keyboard shortcuts to set “Tx even/1st” ON or OFF.

8. A number of (mostly minor) bug fixes and tweaks to the user
interface. For example: new behavior for the audio level slider;
correctly logged QSO start times in certain situations; correct
control of FT-891/991 and some other radios via rigctld.

At the time of the v1.8.0-rc1 release the following tasks are yet to
be completed:

1. Updates to WSJT-X User Guide.
2. Sample files for FT8.
3. Enhanced FT8 decoding using AP (“a priori”) information.
4. Signal subtraction and multi-pass decoding for FT8.
5. Option for FT8 to Auto-respond to the weakest responder to your CQ.

 

Installation packages for Windows, Linux, OS X, and Raspbian can be
downloaded from the WSJT web site:
http://physics.princeton.edu/pulsar/K1JT/wsjtx.html

Please send bug reports to either or
Such reports should include a full
prescription of steps to reproduce the undesired behavior. You must
be a subscriber to post to either of these lists.

 

Brief Description of the FT8 Protocol
————————————-

WSJT-X Version 1.8.0 includes a new mode called FT8, developed by K9AN
and K1JT. The mode name “FT8” stands for “Franke and Taylor, 8-FSK
modulation”. FT8 uses 15-second T/R sequences, provides 50% or
better decoding probability down to -20 dB on an AWGN channel, and
maintains good performance on Doppler-spread fading channels. An
auto-sequencing facility includes an option to respond automatically
to the first decoded reply to your CQ. FT8 QSOs are 4 times faster
than those made with JT65 or JT9. FT8 is an excellent mode for HF
DXing and for situations like multi-hop E_s on 6 meters, where deep
QSB may make fast and reliable completion of QSOs desirable.

Some important characteristics of FT8:

– T/R sequence length: 15 s
– Message length: 75 bits + 12-bit CRC
– FEC code: LDPC(174,87)
– Modulation: 8-FSK, tone spacing 6.25 Hz
– Constant-envelope waveform
– Occupied bandwidth: 50 Hz
– Synchronization: 7×7 Costas arrays at start, middle, and end
– Transmission duration: 79*1920/12000 = 12.64 s
– Decoding threshold: -20 dB; several dB lower with AP decoding
– Multi-decoder finds and decodes all FT8 signals in passband
– Optional auto-sequencing and auto-reply to a CQ response
– Operational behavior similar to JT9, JT65

We plan to implement signal subtraction, two-pass decoding, and use of
a priori (AP) information in the decoder. These features are not yet
activated in v1.8.0.

We haven’t yet finalized what the three extra bits in the message
payload will be used for. Suggestions are welcome!

— Joe, K1JT, for the WSJT Development Team

 

 

 

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