The TDU-4000 provides protection for phones from being used as clandestine listening devices. The unit electrically disconnects the telephone line from the phone when the phone is in the “on hook” position. During disconnect the telephone line is left open, while the voice path on the phone is grounded. This disables room audio from being transmitted onto the telephone line to prevent any eavesdropping. The phone will only connect to the telephone line when it is in the “off hook” position. The “Off Hook” detect and “Ring” detect signals are also opto-isolated from the phone.
A typical link consists of one TDU-4000 with connections to the POTS line and to the subscriber’s phone. FiberPlex recommends “R” units for high security applications because the units have added shielding and filtering for RFI suppression.
Flexible Mounting and Powering Options
The TDU-4000 is part of the FOI line of products designed for ruggedized mil applications. It is housed in the familiar FOI shielded can enclosure. For standalone applications it can be powered by adding a PSQ-3909 AC supply or a PSQ-3920 DC power supply (not included). Optionally, up to 8 FOI units can be mounted on CMA chassis adapters and installed in an RMC-3101 or RMC-2101 rack mount chassis. The units are powered redundantly by a common back plane connection.