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Author Topic: Dumb question RE FT8  (Read 356 times)

Offline BoomboxDX

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Dumb question RE FT8
« on: June 10, 2024, 1120 UTC »
Hi all,
Like many SWL's, I've heard a lot of FT8 in the HF ham bands. Sometimes the presence of FT8 can indicate the propagation of certain ham bands... Not having the decoding software, it's just sick ice cream truck sound on my radios, but I still tune into those channels and mark down the presence of FT8 in my logbook.

That said, I'm curious as to what I'm hearing. It seems that the FT8 signals are time governed, and I can hear that. They all start at the same time.

But what am I hearing? 4-5 stations transmitting simultaneously? Or 10 stations transmitting simultaneously? It sounds like I'm hearing a bunch of them, but I'm not sure.

Also, if there are so many transmitting at the same time, how does the receive software determine what it's decoding? Does it decode all 5 or 6 signals simultaneously, all being decoded at the same time? Do some FT8 signals get flooded out by the stronger signals?

And does anyone use JT65 anymore? The FT8 sounds a lot different than it used to sound in the 2010's.

Thanks for your patience.
Boombox
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

Offline autovon

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Re: Dumb question RE FT8
« Reply #1 on: June 10, 2024, 1204 UTC »
Q:But what am I hearing? 4-5 stations transmitting simultaneously? Or 10 stations transmitting simultaneously?
A: Depending on the band, you might be hearing 5, 10, 20, 30 signals or more at the same time. 

Q:Also, if there are so many transmitting at the same time, how does the receive software determine what it's decoding?
A: The mode/software is pretty amazing.  There is some very detailed reading as to how it goes about doing what it does on the WSJTX page.   Timing is very important with the software and having the computer clock synced within about 1 second is needed.

Q:Does it decode all 5 or 6 signals simultaneously, all being decoded at the same time?
A:  Yes, decodes all of them at the same time.  The user sees this decode right at the end of the 15 second cycle. It's not exactly 15 seconds, but for the purpose of basic understanding, it's 15 sec TX and 15 sec RX.

Q:Do some FT8 signals get flooded out by the stronger signals?
A: Yes, but also again the mode/software is pretty resilient.  It can decode signals that are right on top of each other often times.
Default RX location is Wisconsin using various wire antennas. Other RX will be noted.

Offline skeezix

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Re: Dumb question RE FT8
« Reply #2 on: June 10, 2024, 1504 UTC »
Each of the signals is 50 Hz

This is a screenshot from the waterfall in WSJT-X for 6m, 12m, and 15m.


Minneapolis, MN

Offline BoomboxDX

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Re: Dumb question RE FT8
« Reply #3 on: June 11, 2024, 0526 UTC »
Thank you for your replies. It really helps.
Boombox
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

 

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