Re: [wsjt-devel] FT8 and frequency drift .

[David A. <da...@al...>]

Hi Joe,
This question was pure technical curiosity, I do not ask any improvement.
Bill's answer was very understandable.
Some OMs use TCXOs based tranceiver, and some do not. May it be necessary to
indicate in the documentation of WSJT-X the level of maximum drift which
does not degrade the transmission?
Thank you for your answer,
Have a good day,
David, F4HTQ.

-----Message d'origine-----
De : Joe Taylor [mailto:jo...@pr...] 
Envoyé : vendredi 6 avril 2018 16:56
À : WSJT software development <wsj...@li...>
Objet : Re: [wsjt-devel] FT8 and frequency drift .

David --

On 4/6/2018 9:08 AM, David Alloza wrote:

> I am wondering how we can decode  FT8 message send by a frequency 
> drift transmitter .

> Do we know from what level of frequency drift a message become 
> impossible to decode ?

> Do you have any idea how the minimum SNR decoding level is impacted by 
> a frequency drift?

You don't say what has motivated your questions.  Bill already provided
basic answers corresponding to the "stock" FT8 decoder. There will be little
sensitivity loss for frequency drifts up to ~3 Hz over a 12.6 s
transmission.  Things will degrade significantly if the drift is much
larger.

With sufficient motivation, it would not be very difficult to add "AFC" 
capability to a specialized FT8 decoder.  WSJT-X already includes such
features for JT65 and JT9.

	-- Joe, K1JT

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