For the last several days, I’ve been running the latest version of wsjtx using my RFSPACE SDRIQ software defined radio, and just logging the results. Previously, for most of my JT65 needs, I used JT65-HF, but I was interested in trying out the JT9 mode as recommended to me by numerous hams. JT9 uses a similar (the same?) encoding as JT65, but in a much narrower bandwidth. The current usage seems to be that for JT65, JT9 signals are 2Khz (or 2.5khz) higher in the band. What’s cool about using my SDRIQ as a monitor is that I can set it up to pull in 4Khz, and WSJT-X will decode both JT65 and JT9 signals at the same time. Because JT9 isn’t quite as popular (yet) that is rather convenient: you get twice the modes/signals for the price of one!

But this has led me to wonder: JT9 sends the same information in the same time, but with drastically reduced bandwidth (less than 10%). Why use JT65 on HF at all? Joe Taylor (Nobel Laureate, and author of WSJT-X) says that JT9 was optimized for “MF and LF”, but doesn’t really hint at why it wouldn’t be better more universally. Does anyone have any ideas where JT65 might be better? If not, then shouldn’t we all be good citizens and move towards JT9?

Just curious.