Radio Preppers

General Category => Digital Modes => Topic started by: NCGunDude on October 31, 2017, 12:55:16 PM

Title: FT8 digital comms mode
Post by: NCGunDude on October 31, 2017, 12:55:16 PM
I've been using PSK-31 for a couple of years, and tried JT-9 and JT-65. Last weekend updated WSJT-X on my linux box and started making contacts.

FT8 supports up to 28 characters in 15 second send/receive intervals. It's necessary to keep your clock synced within 1 second of UTC. According to the documentation, FT8 is not as sensitive as the JT protocols, but is much faster.

While it's a fun, fast paced protocol, I can see it's usefulness in a grid down situation for sending abbreviated messages.

The time syncing issue has me thinking how would one accomplish syncing their computer without an internet connection?

Anyone else trying FT8 and what do you think?
Title: Re: FT8 digital comms mode
Post by: gil on October 31, 2017, 01:04:19 PM
There are much better modes for chat than FT8.
Those "chatless," time-dependent modes are useless for prepping.
FSQ or Olivia come to mind, much better. I should be testing them soon.

Gil.
Title: Re: FT8 digital comms mode
Post by: RadioRay on November 01, 2017, 10:37:36 PM
For communication, I've found that CONTESTIA 4/250 has a very good resilience -vs- speed and bandwidth. For communication, you rarely if even need the full ASCII set.  Using only uppercase, nimbers and most punctuation, CONTESTIA has a shorter data set (bits per letter) and so sends fewer bits for the same letters. It uses a STRONG FEC like OLIVIA and works well into the noise.  Unlike the 2-way beacon modes, which at first seem great for prepping, there is no timebase needed.  Most of the 'low power' beacon modes use internet clocks or GPS slaving - both of which are questionable in a SHTF situation. I did a full evaluation and the time synch is a major problem - after all, if we HAVE the internet, we'd use the internet.

My 0.02 Euros worth - please adjust for currency devaluation, Brexit & etc.

 de RadioRay ..._  ._

Ps. Remember, for digital QRP,  include the COMPUTER power drain in the power budget calculations. Morse uses no computer, other than the brain.
Title: Re: FT8 digital comms mode
Post by: gil on November 02, 2017, 04:16:36 AM
Quote
I've found that CONTESTIA 4/250 has a very good resilience -vs- speed and bandwidth.

Thanks Ray, I remember you mentioned it before. I'll test it as well. What an awful name though :o

Gil.
Title: Re: FT8 digital comms mode
Post by: RadioRay on November 03, 2017, 10:00:12 PM
"What an awful name though" :o

Mooooo- ha ha ha ha!  True

of course, a REAL CONTESTERS mode would just be hardwired to send "5NN" and maybe their call - 20 KHz high - of course.

Title: Re: FT8 digital comms mode
Post by: gil on November 04, 2017, 04:01:43 AM
Quote
of course, a REAL CONTESTERS mode would just be hardwired to send "5NN" and maybe their call - 20 KHz high - of course.

I think the software would be locked on QRP calling frequencies and 14300. Time between calls would also be hardcoded to 0.1 second. Minimum power 500 Watts.

Gil.