A tone burst decoder requires a specific tone frequency such as 2250 Hz for a specific minimum period of time (120 milliseconds) before it will provide an output. This delay prevents voice signals or other random on-frequency signals from falsely activating the decoder. A function generator equipped with tone burst capability can generate the signals necessary to test the delay time as well as frequency response and sensitivity of tone burst decoders.

1. Connect equipment as shown in Fig. 20. With the generator initially in the continuous run mode, set its range and frequency to the decoder’s acceptance frequency. This should be found in the manufacturer’s service literature or may be marked on the unit. Use a frequency counter if a high degree of accuracy is required.