Caution Urged in Using High Duty Cycle Digital Modes via Satellite

Amateur Radio Satellite FO-29

Amateur Radio Satellite FO-29

A report in ANS-288 discussed an experiment operating with the WSJT-X FT8 digital mode via satellite. Satellite operators have gained more experience with this mode over this past week.

As a result of on-the-air observation other satellite users planning to try FT8 or MSK144 modes via satellite are encouraged use caution using these modes and possibly avoid their use completely in light of problems.

Dave, KG5CCI wrote, “He noticed a very hard time getting into the transponder. The pass was nearly overhead, and the 3w-4w that is normally sufficient was barely cutting it. I also noticed it was ‘up and down’ alot, whereas some moments it was easy to get in, then it would be nearly impossible. There were also pockets of ‘noise’ all over the transponder, that sounded somewhat digital, but I just couldn’t place them.” Further investigation revealed that an MSK144 signal in the transponder passband was causing the problems.

Matthew, NJ4Y noted, “Experimentation isn’t the problem, too much power is. It’s bad enough on SSB, worse with CW, and killer on constant duty cycle modes like FT8.”

To gain a full understanding of the situation readers are encouraged to follow the amsat-bb message thread which can be accessed at

Source: AMSAT News Service