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

[Bill S. <g4...@cl...>]

On 06/04/2018 14:08, David Alloza wrote:
> Dear developers,
>
> 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?
>
> Regards,
> David F4HTQ.

Hi David,

modes used for EME and other VHF and up propagation paths necessarily 
have to deal with changing frequency. I don't believe FT8 has explicit 
compensation. Given that, so long as the drift is no more than half the  
tone spacing over a transmission I doubt there is much impact. So that 
would be a drift rate of less than 12.5Hz/minute (50Hz ÷ 8 ÷ 2 = 3.125Hz 
× 4 per minute), above that degradation will be rapid.

73
Bill
G4WJS.