Why should you not set your transmit frequency to be exactly at the edge of an amateur band or sub-band?

When selecting a transmit frequency for amateur radio operations, it's important to avoid positioning the frequency exactly at the edge of a band or sub-band for several technical reasons. Each of these considerations helps ensure effective communication and adherence to regulations.

Setting your transmit frequency precisely at the edge can lead to modulation sidebands extending beyond the intended frequency limit. Every signal modulates, meaning it generates additional frequencies known as sidebands. If the main signal is at the very edge, these sidebands might spill over into adjacent frequency bands, potentially causing interference to other operators and breaking rules that ensure band integrity.

Calibration error in the transmitter frequency display can also play a role. Most frequency displays are not perfectly accurate, and slight discrepancies can occur, meaning the actual frequency might not be where the operator believes it is. By leaving some buffer space away from the edge, you mitigate the risk of unintentionally transmitting outside of the allocated band.

Additionally, transmitters can experience frequency drift due to temperature changes or other factors. This drift can move the actual transmit frequency slightly over time, making it possible for a transmission that begins within the permitted range to gradually slide beyond it. By not setting the frequency at the band edge, there is a safeguard against such drift leading to rule violations.

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