AM, FM, USB and LSB Explained
Learn what common radio modes mean and why both ends of a contact need compatible settings.
AM and FM
AM varies a carrier’s amplitude and FM varies its frequency. Their audio characteristics, receiver behaviour and permitted use depend on the radio service and equipment rules.
Single sideband
SSB transmits one sideband and suppresses the carrier compared with conventional AM. USB is upper sideband and LSB is lower sideband. SSB is widely used for HF voice and long-distance contacts.
Why tuning matters
SSB voice can sound distorted if the receiver is not tuned close to the transmitted signal. Small tuning adjustments can make speech clearer, but do not transmit outside permitted channel or frequency limits.
Digital modes are different
Modes such as FT8 encode data into a defined signal format. They are not simply another voice setting, and software compatibility, bandwidth and applicable regulations must be considered.
Before changing modes
Read the radio manual and confirm which modes and equipment are permitted for your specific service and country.
Further reading
Always check current rules for the country and radio service you are using. A community convention or software feature is not proof that a transmission is authorised.
This guide is educational and may need updating as regulations, software and community information change. Check linked primary sources before relying on technical or regulatory details.