Amateur Radio frequency allocations require that your TOTAL RF emissions are contained within the allocated Amateur Radio bandwidth.
For example, on 20 meters, the allocation is from 14.000.000 to 14.350.000 MHz. This refers to your total emissions, not simply the Dial Frequency of the radio.
On USB, for example, (or DIGU) your Dial Frequency (or your suppressed carrier frequency) may read 14.348.000 MHz, but you must also factor in the transmit bandwidth of that USB signal, which can be up to 10 KHz wide, depending upon your Transmit Bandwidth settings (Low-Cut and High-Cut).
NOTE: Transmit Bandwidth is NOT the same as the Receive Filter you have selected in your Slice menu. The Transmit Filter Bandwidth is set by the Low-Cut and High-Cut settings in the "Radio Controls" Panel > P/CW sub-panel.
In the picture below, the High-Cut is 2900 Hz (or 2.9 KHz) which would be added to the radio's "Dial Frequency" to get the total frequency occupied by the radio.
Using the dial frequency of 14.348.000 MHz mentioned above, if your "High-Cut" TX filter setting is 3000 Hz (3 KHz) then your total occupied bandwidth would extend from 14.348.000 MHz to 14.351.000 MHz -- which is 1 KHz beyond the band edge of 14.350.000. The firmware in the radio will recognize the RF emissions are beyond the band edge and inhibit transmission. An interlock message is shown on the SmartSDR client software running on a PC, Mac, or Maestro and displays an "Out of Band" warning. Even 1 Hz beyond the band edge is enough to trigger the out-of-band interlock condition.
What does this look like on SmartSDR for Windows?
In this visual illustration, the radio's dial frequency" is set to 14.348.000 MHz.
The thin yellow line to the right of the dial frequency denotes the band edge frequency of 14.350.000 MHz.
The BLUE Bar represents the Receive Filter Bandwidth. (2.7 KHz wide - set from 100 Hz to 2800 Hz)
The Dark RED to the right of the slice RX Filter bar represents the part of the Transmit Bandwidth that is wider than the Receive Filter. Your radio will not normally show this red band, but it has been made visible for this illustration.
The TX Bandwidth "High-Cut" is set to 3000 Hz (3KHz) wide.
RF emissions to the right of the Band edge are "Out of Band" and any RF transmission will not be permitted.
What if you need to operate closer to the band edge?
Reduce your maximum Transmit Bandwidth. For example, If your dial frequency is 14.248.000, your HIGH-CUT must be set to 2000 Hz or less. This will reduce the higher audio frequency of your SSB signal, but you will be able to transmit and work the "rare DX."
Considerations for 60m Operation
In some locations, 60 Meters is authorized only on certain "Fixed" or "Channelized" frequencies that are limited to a maximum bandwidth of 2800 Hz (2.8 KHz). Primarily this is the US and the UK.
In normal operations, this means a Low-Cut of 100 Hz and a High-Cut of 2900 Hz.
If your "High-Cut" is set 2900 Hz or wider, then your radio will be "Out Of Band" and will not transmit.
If your "High-Cut" is set properly, but your dial frequency is off of the channelized frequency, your radio will be "out of band" and will not transmit.
Additionally, if your FT8 program is set for "fake-it" it will often shift the dial frequency up or down, possibly resulting in an out-of-band interlock condition when transmitting, which will trigger an "Out of Band" warning and inhibit transmission.