Since ICOM no longer produces the ICF-121, official sources are limited, but users can still track down the manual via:

Four dealer-programmable keys that can be assigned specific functions (e.g., Scan, Scrambler, or Emergency).

Disclaimer: Ensure you are using the correct manual for the VHF IC-F121 and not the UHF IC-F221, although many operating procedures are shared between the models. If you'd like, I can help you: Find the specific needed for programming Explain the pinout for the microphone connector

Rotate the volume control knob clockwise until a click is heard. The display will momentarily light up all segments before displaying the last selected channel. Rotate the knob further to set the desired audio level when receiving a signal. Selecting Channels and Zones

The Icom IC-F121 is a rugged, commercial-grade VHF mobile transceiver built for public safety, business, and industrial communication. Known for its durable construction and straightforward interface, it remains a reliable choice for mobile fleets.