ReverseFrequency

That is, the transmission frequency and receiving frequency of the intercom will be swapped, and the setting of the setting is also interchangeable.

When there is a relay, one party does not use relay or relay suddenly does not work, but is a common way to use the two receiving frequencies of relays. The inverted frequency connection has a signal directly (not through the relay), and does not change the method of using the other party's use of relay, so it is suitable for direct testing in the case of unknowingly.