signal chain
RF, IF and LO Explained
The three frequencies in a heterodyne receiver, why the image sits 2 × IF from the wanted signal, and how that plan decides the preselector and the local oscillator.
Section
RF Signal Chain
System-level guides to RF, IF and LO planning, up and downconversion, mixer conversion loss, image rejection and preselection.
How frequency sources, mixers, filters and amplifiers combine into a working receiver or transmitter chain.
Start with RF, IF and LO explained — the three frequencies, the image at 2 × IF, and why the IF filter cannot reject it. Then upconverter vs downconverter if the question is direction rather than placement.
The hardware that usually implements the preselector and the LO is in YIG-tuned filters and YIG-tuned oscillators.
signal chain
Upconverter vs Downconverter
Downconverters translate RF to a lower IF; upconverters translate IF to RF. Same mixing identity, opposite direction — the unused product is a frequency-plan problem in both.