Empty signal detector

Application Number: 00103261
Application Date: 2000.03.20
Publication Number: 1274212
Publication Date: 2000.11.22
Priority Information: 1999/3/18 JP 72931/1999
International: H04H1/00;H04L27/32
Applicant(s) Name: Matsushita Electric Industrial Co., Ltd.
Inventor(s) Name: Sato Kazuhiko;Segawa Hiromoto
Patent Agency Code: 72002
Patent Agent: han hong
Abstract A null signal detecting device, wherein when digital information is transmitted via a plurality of frame signals, a null signal is inserted between each of the frame signals to identify each of the frame signals. The null signal has an amplitude smaller than that of each of the plurality of frame signals. The plurality of frame signals and the null signals are subjected to frequency division to generate a plurality of carrier waves which are then modulated. The plurality of modulated carrier waves are transformed into an RF signal which is then transmitted as digital information. The null signal is detected by demodulating the RF signal. The null signal detecting device includes a frequency transformer section for transforming the RF signal into a signal having an intermediate frequency fC; a band pass filter section for receiving an output signal from the frequency transformer section and extracting a signal having a frequency band width fB around the intermediate frequency fC such that the plurality of modulated carrier waves are included therein; a null signal detector filter section including a filter and a null signal detector section.