The Walker PTT-500M-NC-1 Push-to-Talk (PTT) handsets Address the need for security in environments where background conversations must not be over heard on the telephone. With a Walker PTT handset any conversation can be conducted without the worries of eavesdropping. PTT solutions are also recommended for environments with loud intermittent background noise. This handset (PTT500MNC1) includes a pre-installed noise canceling microphone (NoiseCensor ). The Walker Noise Censor reduces sidetone noise up to 80%, making calls clearer for the user. Technical Features: Transmitter Type: Carbon Compatible Electret (ET). The transmitter element is designed into an amplified circuit to act as a Carbon microphone without variations PTT handsets do not require a hook switch in the cradle G-Style / 500-Style: Round Receiver & Transmitter Ends Connector: 4 conductor modular jack (RJ22) Compatible with Cortelco 2500 and 2554 series telephones Color: Black (00) Installed Upgrades: NoiseCensor: (NC-1) A unique noise canceling system using directional microphone housing. Output Level@ 1000 Hz: -26 dBV (98 dBSPL) Frequency Response:180 Hz to 5000 Hz (meets EIA RS-470) Output Impedance: 50 Ohms nominal Cancels Noise: up to 30 dB Receiver (@ 1000 Hz) Output Minimum (-20 dBV drive): 96 dBSPL Input Impedance: 150 Ohm Amplitude Limiting: 124 dBSPL Receive distortion: less than 5% Compatible with hearing aids