UAVcast is working very well with Ardupilot but I think the water environment is causing a bit of a problem. See above link. @Sinamics
I added two small whip antennas with crc9 connectors to the modem and now everything works fantastic. So this problem is solved
Good to hear that David.
You had the antennas sitting around at home but did not use them before right.
Can you please share a link to the antenna product? There are several different types…
I will be where you are sometime in the future 
Karl
Yes I had these already on hand but did not try them until yesterday.
They don’t look like much but made a huge difference.
Ah thank you. You have the long antennas, I think there are some short models as well.