GRANIT-8 telephone line protection filter is used to protect voice data against leakage through the two-wire lines of open telephone, conference and dispatch communications by way of acoustoelectric conversion.

The filter is meant to let the voice frequency band signals through under the normal mode of phone line’s operation, and weaken the high-frequency signals that can be supplied to the line in the event of high-frequency intrusion.

The Product is a four-terminal device that consists of two U-shaped inductive-capacitive segments and one diode bridge. The circuit’s diode bridge represents the Product’s input and is used to decrease the transmission coefficient under low signal levels. The signals that can be generated on the output of IT devices as a result of acoustoelectric conversions are suppressed. The circuit’s filter serves as an output segment of the four-terminal device and represents a low-pass filter with the cutoff frequency of no more than 28 KHz.