I have built probably the easiest, reasonably rugged and most cost-effective 100mW WSPR (or FT8) beacon.
The Build
Here is my quick and dirty build with whatever I had lying around:
We have replaced the traditional expensive Mini-Circuits transformer with a cost-effective Bourns coupled inductor.
Analysis
Power consumption: Before RF generation starts ➔ 20mA @ 5v. After RF generation starts ➔ 52mA @ 5v. So the power input consumed in the RF generation process is more than 150mW it seems (which is good).
Theory
The first law of thermodynamics states that total energy of an isolated system is constant, energy can neither be created nor be destroyed but can be transformed from one form to another. We do not want to break it ;)
Results
Results: 6.6 Vpp sine'ish wave on the scope @ 28 MHz!
Cost
Cost: Around 600 INR. This can be easily reduced to 300 INR by using Adiy LuatOS RP2040 board! Beat this ;)
Software
Time to build: Less than 15 minutes
Software link: You can use pico-WSPR-tx or Pico-FT8-TX.