What is the purpose of delaying RF output after activating a transmitter’s keying line to an external amplifier?

When using an external amplifier, the transceiver must signal the amplifier to switch its internal relays from 'receive' to 'transmit' mode. This action physically disconnects the antenna from the receiver and routes it to the amplifier's high-power output. Because these relays are mechanical devices, they take a few milliseconds to physically move and settle. If the transceiver starts outputting RF power before these relays have fully closed, a destructive condition known as 'hot switching' occurs. Hot switching forces high-power RF energy to jump across the tiny gaps in the moving relay contacts, causing severe electrical arcing. This arcing can permanently damage the relay contacts and potentially harm the transceiver or amplifier. Delaying the RF output ensures the mechanical connection is solid before power is applied.