Re: Over-Driven FT-8 QRM #FT8 QRM #FT8


Tony .

These modes  are  ' base band heterodyned'  as in the  generation  is  performed  at the  base band , in this case  audio  ,  the  ' waveform'   is then  heterodyned / mixed to the  wanted  frequency ,   the  opposite  of the  RX process ,  where  audio is  presented to the  DSP , after the  RX has recovered the  'Audio  wave' , Tx power should not  alter the  side band ratio  ,  as long  its  its linear , 

Alc could  provide a  leading edge over shoot  and tilt  of the  TX envelope , that's something,  the on/off  keying  , deployed in 
Opera  is  susceptible too , its necessary to  reduce the  drive to the  onset of  ALC to  prevent a  spike on the  leading  edge,if the  audio  keying  is used , 

Replacing the  CW-Key  on the  other hand ,  the  signal  utilises the  TX envelope  shaping , the  system was developed , using the  20 wpm  test signal from the  racal ma1723 as the  standard  'shape'  

Power wise ,  that's  a  unfortunate situation , the  concept of  narrow b/w  short burst signal is really  counter productive , as can be seen from the levels  deployed ,  multiple  access  at  low s/n  is best provided  by  the  appropriate  techniques , making  use  of the  SSB b/w channel ,  requiring a  second  layer in the  coding    applied to the  'modem' ie the  tone placement  routines . 


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