Quantity   Component name
1 × Blue Pill the ever-popular STM32F103C8 development board
1 × ublox NEO-6M GPS module an extremely common GPS module breakout board
1 × Si5351A breakout board a popular frequency synthesizer module
1 × Low-pass filter for harmonics as per band of interest For the 20 m band, I constructed a 7-element chebyschev with 2 pcs 180 pf, 2 pcs 390 pf, 2 pcs 0.77 uH, and 1 pcs 0.87 uH. The coils were hand-wound on T37-6 (yellow) toroids using #24 magnet wire. See post [Harmonics](https://hackaday.io/project/166875/log/167791-harmonics) for more details.
1 × Power Amplifier Not strictly required; the Si5351a can provide about 11-12 mW which is enough for WSPR in some cases, but you might like a power amplifier to get a little more energy out there. I built a simple class E amplifier to get about 10x that output. Details in the log https://hackaday.io/project/166875/log/168080-power.