I've been watching this thread with interest, having recently taken the plunge and experimented with FT8 (but got bored very quickly!). Three comments on aspects that I don't think have been covered:
1. FT8 is very new (albeit it seems to be taking the world by storm) and I suspect many operators are unaware of where it exists on the bands, unless they are data modes operators themselves (which, typically, many long-term topband operators are not) 2. Many FT8 "users" are actually computers - I know of a number of folk who have automated FT8 to the extent that they go to bed at night and in the morning look to see what their PC has "worked". As far as I know, their PC doesn't specifically check for a clear channel although it will normally be trying to find a slot between other FT8 signals within the audio bandwidth. 3. Apropos of which, most FT8 QSO are split frequency - it makes no sense to call a station co-channel. So even if a frequency appears to be clear, it may be that there is a station already in QSO with an FT8 QSO partner 1kHz or more away (the WSJT software handles this "split" operation automatically). So a quick "QRL?" will not be heard. As is usually the case in life, nothing is simple! 73 Don G3XTT On 29 November 2017 at 15:49, Roger Parsons via Topband < [email protected]> wrote: > 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 > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
