Topband: FT-8 question

[Jim Thomson]

Folks on FT-8 use a 2.5 khz  ssb wide RX  filter.    FT-8 is supposed to be good for 20 db  below the noise floor. 
I assume that means 20 db below the noise floor of the 2.5 khz RX filter ? 

But a 250 hz cw filter would drop the noise floor by 10 db... vs the 2.5 khz wider filter... if CW mode used. 

So  if Im reading this correctly,  FT-8 mode, using a 2.5 khz filter....is really only 10 db better than a 250 hz cw filter, using cw mode ? 

If that is the case,  being able to copy signals 10 db  weaker than the noise floor of a  250 hz filter is still nothing to sneeze at. 

The issue I see with FT-8.. on any band is the requirement for a  2.5 khz filter.... and possibly being prone to qrm. 

Right now, my issue is extreme high noise levels on 160m... on a 100 by 130 city lot.    Point a semi directional RX ant in the desired direction.... and its 
also pointed at a noise source.  Seems like I am surrounded by noise on 160m.   Im going to drag out by noise canceller and try some more rx experiments,
b4 I throw in the towel.    FT-8 might just be an option for folks like myself that are plagued with high levels of noise.   Another possible option might be 
the use of real time  remote RX.   Another possible option might be using my 80m rotary dipole for 160m RX.   As is, its infuriating listening to high noise 
levels on 160m.   If I cant hear on 160m...except for the usual louder stations,  Im not going to even try TX. 

I have tried using a pair of  500 hz filters, and also a pair of 250 hz filters, and also a 125 + 250 combo, in both my MK-V..and also 1000-D. 
The MK-V also has a 240-120-60hz  dsp filter.  The 1000-D has a tunable audio cw filter.   The problem with the narrow xtal filters is...
with noise levels so high, the noise...  rings out the filters.   The signals coming out of  each filter... get stretched a bit in time duration.
What Im left with is this mess whereby the desired signals +  noise end up all mashed together.  Typ noise on 160m, using a 2.4 filter
is S9 to S9 + 10 db.   Right now, Im trying to evaluate if 160m is even worth the effort required.   Are the  rest of you on 5 acres out in the woods ? 

Jim   VE7RF