Radio Room Clock

## Maritime radio facilities were mandated to maintain silence on two frequencies: 500 kHz for Morse code transmission, and 2182 kHz for voice communication. The silence intervals varied throughout the hour. From 15 to 18 minutes past the hour and from 45 to 48 minutes past the hour, silence was obligatory on the 500 kHz frequency. Additionally, on 2182 kHz, silence was required from the beginning of the hour for three minutes and again for three minutes following the half-hour mark. These regulations aimed to ensure efficient communication by allowing essential messages to be transmitted without interference during designated periods. This protocol was critical for maritime safety, as it facilitated clear communication between vessels and shore stations. By adhering to these rules, radio operators could maintain effective channels for distress calls, navigational assistance, and operational coordination. These practices upheld the integrity and reliability of maritime communication networks, fostering safer navigation and response to emergencies at sea. Compliance with these regulations was imperative for all maritime radio stations to fulfill their duty in facilitating secure and efficient communication within the maritime community.

According to 47 CFR 80.304, maintaining radio silence on 2182 kHz remains mandatory, as specified during silent periods.

As a reminder, on a ship’s radio room clock, the intervals of silence on 500kHz would be indicated by shading the sectors from h+15 to h+18 and h+45 to h+48 in red. Similarly, sectors from h+00 to h+03 and h+30 to h+33, corresponding to the silence periods for 2182 kHz, would be marked in green.

Anyone violating the regulations would promptly receive “QRT SP” in Morse Code, signaling “STOP SENDING — SILENT PERIOD!”

I created a digital clock software for my shack that emulates the design of a Radio Room Clock.