I just posted this in another thread.

I’m just staring to build a T41 SDR QRP Transceiver

SDR = Software Defined Radio, 
QRP is the Q code for reduce power, QRP radios are meant for low power operations.

Not sure if you want to go down the kit route but it will teach you a bit about RF (Radio Frequency) theory and practical electronics (If you don’t already know). It’s also very modular and there are other options for the RF amplifier section so it does not have to be QRP, there is a 20W and 100W board available as well.

Be warned that this kit will take a lot of time, reading, careful soldering of tiny SMD (Surface mount devices) components, etc. There is a good book about the kit, the theory, programming the Tensy (the microcontroller heart of the t41), etc.

http://4sqrp.com/T41main.php

https://www.amazon.com/Software-Defined-Radio-Transceiver-Construction/dp/B09WYP1ST8

Note: I know most in this community will know the acronyms, I spell them out for others that may happen by