locked Re: Theoretical maximum for one FT8 band channel? #FT8

Bill Somerville

On 21/01/2021 14:11, Bruce KX4AZ wrote:
With the ever-increasing popularity of the FT8 mode, there are times when I am decoding in excess of 36 stations on a single channel (JTAlert display slot maximum).  And I am practically forced to transmit on a slot that straddles two adjacent stations, hoping that increases the chances of being decoded, without impairing the neighbor's decodes.

This has me wondering if anyone has ever tried to estimate the theoretical maximum station capacity of a 0-2500 Hz FT8 channel, beyond a simple non-overlapping calculation (using the individual FT8 signal bandwidths).  Given all of the variables (signal strength, timing, degree of overlap, etc) this would be a challenging calculation, but maybe an idealized case with all the same strengths & 50% overlap might be possible.  And the way the software uses the subtraction & additional decoding passes you can even have stations sharing the same audio channel, which I find amazing.

Lacking a theoretical calculation, it would be interesting to hear what maximum station counts people have observed when a FT8 band is packed full.
Hi Bruce,

we have example .WAV files that decode as many as 60 signals. Of course propagation variations and geographical distribution will mean that many more stations can be actively engaged in QSOs on one SSB width channel World wide. Those with SDRs and other receivers with wider bandwidths can extend their operation to more than a typical 2400 Hz width, others less fortunate can always tune up of down a bit to capture signals of interest, even though they may not be able to decode all signals present at once.

One thing is certain, if everyone obeyed there licence conditions and used the minimum power necessary to complete QSOs there would be even higher occupancy.


Join main@WSJTX.groups.io to automatically receive all group messages.