I agree with the comments thus far.  I also think there is a factor associated with the "robustness"  of PSK31 or lack thereof when compared to JT65A.  When i try PSk31 with basic wire antennas I frequently lose the contact after a brief exchange of a few sentences . Also, more often than i would like, with PSK31 I work a weak signal only to have another QSO start on top of my desired signal.  With JT65 this is much more rare, usually what you first decode is able to hold out for the 2-3 exchanges and less susceptible to QRM . 

Andy K3UK

Andy,  That's  quite so, but there is also ,as to  exactly what is  being  compared ,  psk is free running  live qso mode , where the  JT system's are  beacon , fixed format , psk is susceptible to path  phase distortion' rendering the  signal undetectable,  where as the  JT system in there  data 'decode' state are mfsk and as  such more  robust , in correlation,  [deep-s] the  whole of the  Tx is  treated as a single 'bit' , this  gives additional  processing  gain , whereas psk requires  round -10 -12 dB s/n ,  mfsk may achieve another  -10 dB [ or  save x 10 power] , the  idea of  multi pass , also enables additional  - dB's  to be achieved. 

I suppose the  split is ,  beacons, where the  detection  of the  other  station is  all important , or  live  qso , where the  accuracy of the  recovered data  payload is paramount ... more  concerning , in diminishing  'bandwidth'  is the  rush to  high speed wide  system's that  are capable of  only  supporting a  single  data  channel , 

73-Graham

G0NBD