US 4,048,619 A · Secure two channel SCA broadcasting system

Abstract

A secure information broadcasting system including a central broadcasting station for encoding data in binary form utilizing a keyword and transmitting on one frequency a FM-SCA signal phase shift modulated by the encoded data. The encoded data is also supplied to one or more remote broadcasting stations, typically via telephone lines, where it is transmitted on a second frequency as a FM-SCA signal phase shift modulated by the encoded data. Each remote station transmits a relatively low power signal in a predetermined local area, such as an office building, while the central station transmits a relatively high power signal in a general area including one or more of the local areas. The general area signal is transmitted with a time delay relative to the remote stations. Each of a plurality of portable receiving terminals has an identification number stored therein. When a subscriber desires to display the broadcast information on his terminal, he enters a unique password which is combined with the identification number to generate the keyword. The keyword is utilized to decode the received binary data. The terminal alternately tunes in the two frequencies and will lock on the first frequency signal when the terminal is within the general area but outside the local areas. The terminal will lock on the signal first received in the local area and a reset switch is provided to force the terminal to lock on the second frequency signal when the first frequency signal is present and is first selected in a local area.

Claims11

Dependent claims

A secure two channel information broadcasting system comprising:

a central broadcasting station for encoding and transmitting, as an SCA component of a FM carrier signal having a first frequency, data received from an information source;
a remote broadcasting station for transmitting, as an SCA component of a FM carrier signal having a second frequency, said encoded data received from said central broadcasting station;
and
a terminal for receiving, decoding and displaying said encoded data including means for receiving FM carrier signals in a frequency band including said first and second frequency carrier signals, means for alternately generating first and second reference signals each having a frequency which differs by a predetermined frequency from the frequencies of said first and and second frequency carrier signals respectively, means responsive to said receiving means and to said reference signal generating means for combining said first frequency carrier signal with said first reference signal and for combining said second frequency carrier signal with said second reference signal to generate a difference signal having said predetermined frequency, means responsive to said difference signal for detecting said SCA components and for directing said reference signal generator means to continue to generate the one of said reference signals associated with the one of said carrier signals having its SCA component first detected whereby said receiving means locks on said one carrier signal, and means for decoding and displaying said encoded data from said SCA components of said carrier signals.

1 more element

Dependencies are inferred from the claim text.

Secure two channel SCA broadcasting system

Life of this patent

Secure two channel SCA broadcasting system

Life of this patent

Abstract

Claims11