An impulse that, in a neutral circuit, causes the loop to open or causes absence of signal. In a polar circuit it causes the loop current to flow in a direction opposite to that for a mark impulse. A space impulse is equivalent to abinary zero.

• 在中性电路中，引起环路断开或造成信号消失的一种脉冲（信号）。在极性电路中，空号脉冲促使环路电流向传号脉冲相反的方向流动。空号脉冲相当于二进制零。