What do you need to make a radio transmitter? There are builds that work with just a couple of transistors. But how about a GPS-disciplined small signal beacon? You can actually get the job done for less than the cost of a fancy hamburger, thanks to [RPiks]’s pico-WSPR-tx and the Weak Signal Propagation Reporter Network (WSPR).
WSPR is a digital protocol where a beacon encodes its callsign, location, and transmitting power, and then sends it out to a network of receiving stations worldwide. The idea is to use the data coming from the beacons to determine whether radio propagation conditions are good or not; if you hear a quiet signal from afar, they’re good in that direction. [RPiks]’s beacon design simply includes a Raspberry Pi Pico and a GPS receiver. Everything else is software.
Of course, this means that it’s using the Pico’s GPIO pins for transmission. Maybe you want to add some filtering to take off the rough square-wave edges, and/or maybe you want to boost the power a little bit with an external amplifier. If so, check out our own $50 Ham column’s advice on the topic. But you don’t need to. Just a Pico and a GPS should get you working, if you want to test the WSPR waters.