I have seen this sort of post many times on the Forum and FB and I wanted to throw some of my observations out there. Many times, I see a CQ and I do respond but many times do not get a connection. Sometimes it could be that the station is already in a QSO but I am also seeing another issue with stations where the SNR is severely imbalanced.
In the example below I am decoding a station 20dB better than they can hear me running 80W. If the path were worse and I was not receiving the other station at +5 to +10dB, but say -10dB that would put my signal way down from what VARA can decode, and -10dB is not a bad signal.
I see this phenomenon frequently.
Conversely there are many stations where we have a very balanced SNR, even through a long QSO. Both stations running like power. With SNR in line like this the data transfer goes very smoothly and fast.
Why there are some instances where the SNR is so out of wack could be high noise floor at the station, or improper level settings in VARA.
In my case, I have a nearly constant S6 noise level on 20, and worse reception on 30. I think it's astounding that the VARA-HF software modem works as well as it does! Thanks for the well thought out post, Gary.