Topband: FT8 qrm

[Roger Parsons]

Perhaps I shouldn't have started this thread! 


The whole point of my original posting was that I was definitely transmitting more than 500Hz HF of the FT8 tones, so from an 'analogue' perspective there should have been no problem. As others have mentioned, FT8 is received though an SSB bandwidth filter. Where wideband noise is the limiting factor on reception (eg VHF) it is a valid technique to put the ultimate selectivity at the end of the receive chain. It is not valid where there are likely to be strong signals from some other mode within the receiver IF passband. Therefore, my opinion FT8 (and many other digital modes) are not suitable in situations where there is intense activity on nearby frequencies. I think it is unreasonable to suggest that there should be an unused 'guard band' just to overcome receiver and system deficiencies. 


(And of course I am aware that these limitations could be overcome using SDR architecture, but that is another story.)


73 Roger
VE3ZI