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

Setting your transmit frequency at the edge of an amateur band or sub-band is not advisable for several important technical reasons.

First, if transmission is at the exact edge, even slight inaccuracies in the calibration of the transmitter’s frequency display could mean that the actual transmitted frequency may extend beyond the allowed band limits. This could lead to unintentional interference with adjacent bands, which is against regulation and can cause problems for other operators.

Additionally, modulation sidebands—the extra frequencies produced alongside the main signal during modulation—can extend outwards from the carrier frequency. If your carrier is positioned right at the edge of the band, these sidebands may unintentionally spill over into frequencies that lie outside the legal operating range. This can create harmful interference to other users on adjacent frequencies.

Lastly, even small variations in temperature, power supply changes, or mechanical shifts can cause frequency drift. Such drift might change the actual frequency being transmitted, which again could push the signal outside permitted limits.

Because all of these factors—calibration errors, modulation sideband extension, and potential frequency drift—are relevant to the operation of an amateur radio transmitter, selecting a frequency comfortably within the band is essential to ensure compliance with regulations and to minimize interference with others. Hence, the comprehensive rationale