The DX Engineering TVSU-1A Time Variable Sequencer Unit is a microprocessor-based transmit/receive control signal delay unit. It provides 0-30 ms of delay programmable in 2 ms steps to as many as five outputs tied to the CW keying or push-to-talk (PTT) lines.

By controlling the receive-to-transmit (and back) timing of linear amplifiers, preamplifiers, and other sensitive equipment, damage caused by improper switching can be eliminated. This sequencer improves CW performance by eliminating annoying leading edge chopping or truncating of Morse characters. This is especially important in contests or pileups where sending accuracy is critical.