The paper considers the features of using signals of modern telecommunication systems in passive radars. The signals of modern systems of the 4th generation, WiMAX, LTE as well as digital TV signals by DVB­T2 standard may be used as sounding ones. The authors have studied the frame structure of the systems listed; the main signal parameters, such as a band, pulse duration, output power of a transmitting set, system operation frequency range were introduced. The paper presents the main factors affecting the system power budget as well as the values of radar cross section of targets which can be detected. The authors obtained the dependences of the system power budget on the target radar cross section at operation by the signals of WiMAX, LTE and DVB­T2. The highs and lows of the listed systems signals when using them in passive radars were described.