Having a look at the SMD Regulator ICs in LMR SDR 1.1

The AMS1117-5.0V is a popular low-dropout (LDO) linear voltage regulator designed to provide a stable 5V output at currents up to 1A. It is widely used in electronic designs like Arduino and ESP8266 projects due to its efficiency and compact surface-mount size. In the LMR SDR 1.1 circuit it takes 12V from the power supply and gives an output of 5.0V for the corresponding power rail which goes to some integrated circuits, transistors and the next level regulator IC AMS1117 3V3.

AMS1117 3V3 is taking the 5V output from AMS1117-5.0V and giving an output of 3.3V. That gives power to the clock generator circuit with Si5351. 3V3 rail powers another IC in the LMR SDR circuit as well. The AMS1117-3.3 is a popular Low Dropout linear voltage regulator used to provide a stable 3.3V DC output. It is widely used in hobbyist electronics, specifically for powering 3.3V components like the ESP8266 and ESP32 from a 5V or higher source.