I have made some changes to the code I found in this group's file download section to do some testing. I am deciding whether I would need to increase the RF output of the SI5351 to ensure its reports are heard during a balloon mission. I am still waiting for parts to build the amplifier to get 200-500 milli-watts output to the antenna.
In the mean time, I have been running a WSPR transmitter using a SI5351 module with the output at about 10 mW. I am in northwest Ohio, USA, and have received reception reports from Alaska to Germany to Brazil; over 1000 reports a day. So I'm not sure if spending the additional amperage would be worth it when sunshine and supercaps are all I have for a power supply.
My antenna right now is longer than what I will have on the flight, but it's fun to check out the results. If interested, check out the W8AN TX reports at and .
The transmitter is just an Arduino Nano connected to a generic Si5351 module. There is a GoouuuTech GT-U7 GPS module attached for position and time information. My antenna is a 160 meter off-center-fed Windom up about 35 feet. I do have 5 low pass filters from that are switched in based on the band of transmission.
Steve S
Steve S