I'm not sure how many people have actually compared the new digital
modes with CW as far as low signal level decoding. I did that for a
long time when JT-65 first became available. Back then it was much
easier to separate one station and compare the reported S/N to what I
see on my receiver when using a very narrow passband. There was always
a huge disparity, usually 30 to 40 dB. Most of those numbers were taken
right off the main screen of a TS-990s, so the accuracy may not be a lot
but it's a pretty good indication of how close the signal is to the
noise floor.
Then I found this:
http://www.arrl.org/forum/categories/view/31/page:2
You have to sign in to the ARRL site and look for the article titled
"JT65, JT9, FT8, SNR explained".
That article says that the S/N reported by JT-65 is actually 29.7 dB
more than it should be and JT-9 is 31.6 dB more than it should be. That
agrees pretty closely with what I have been observing although my
measurement show a slightly larger difference than that, but that could
be because my measurements didn't have enough accuracy.
I used to try to identify a signal at that was close to the noise floor
and see if JT-9 would decode it. It never did. At a level where JT-9
does decode the signal, it would have been easy copy on CW. So for me,
I see no low level signal advantage to these digital modes. I continue
to wonder why other people say there is. I wonder if others are using a
wide passband when making comparisons (if they really do make
comparisons). For low level CW I usually use 150 Hz, sometimes a little
less if there is QRM.
Jerry, K4SAV
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