In a polar circuit it causes the loop current to flow in a direction opposite to that for a mark impulse.

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。

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In a polar circuit it causes the loop current to flow in a direction opposite to that for a mark impulse.

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。

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