A method of communicating between a transponder and an interrogator. The interrogator (10) transmits a wireless RF interrogation which is received by the transponder (12). The transponder (12) then transmits a wireless RF response. The wireless RF response has a first channel response centered at frequency FDX1=RF+SC, a second channel response centered at frequency FDX2=RF-SC, and a third channel response centered at frequency FDX3=SC. The third channel response is a spurious signal resulting from using a non-linear element (32) as the transponder modulator (32,34). The interrogator (10) receives this wireless RF response. The response is received in the three channels with a first circuit (82) operable to receive said first channel response, a second circuit (86) is operable to receive said second channel response, and a third circuit (86,88) is operable to receive said third channel response. A controller (102) then selects the response from one of said first, second, or third circuits (82,86,88) for demodulating. A demodulator (100) may then demodulate one the selected channel responses. Other arrangements, systems, and methods are disclosed.
A method and apparatus for accurately decoding a Manchester data stream having transition time distortion and noise spikes. Briefly, in an embodiment using a protocol where a falling edge at the mid-point of a bit represents a "1" bit and a rising edge at the mid-point represents a "0" bit, the coded data can be accurately determined by comparing the time period tp.sub.1 from the start of the bit to the first falling edge and the time period tp.sub.2 from the last rising edge to the end point of the bit. If tp.sub.1 is less than tp.sub.2, the bit represents a bit value of "0" and if tp.sub.2 is less than tp.sub.1, the bit represents a bit value of "1".
A high gain input stage for a radio frequency transponder uses an amplifier for increasing a magnitude of an input signal. A DC bias circuit is used for controlling the operation of the amplifier. A resonant circuit is coupled between the amplifier and the DC bias circuit. The resonant circuit is used for receiving a signal generated by an electromagnetic field and for generating the input signal which is amplified by the amplifier. The resonant circuit has an inductor which is used to bias the amplifier thereby removing the need for a decoupling capacitor between the tuned circuit and the DC biasing of the amplifier. Multiple transponder inputs may be implemented in a single integrated circuit package.
Airplanes have transponders which receive and transmit signals to communicate information regarding the flight of the airplane. A transponder testing apparatus is integrated into the transponder and verifies that the transponders are operating in accordance to Federal Aviation Regulations.
A security system which is suitable for use in a vehicle. The security system is a passive entry and passive re-mobilization system in which a security controller transmits a command signal LCs to a remote transponder, which replies with a LF response signal LRs. If an LF response signal is not received in response to the transmission of a command signal LCs, the security controller re-transmits the command signal, again as an LF command signal LCs. On determining that a command signal is a re-transmitted command signal, the remote transponder re-transmits the response signal as an UHF response signal URs.
A self-tuning receiver/decoder for reception of FSK data transmission. An RF stage with resonant circuit (10) is tuned to a first of four possible transmitted frequencies for reception of such frequencies according to interrogation at such frequencies in sequence. Threshold (18) and counter circuits (12, 16) detect each frequency shift change of transmitted frequency and accordingly retune the resonant circuit to a subsequent unknown frequency by counting through a predetermined sequence for possible reception of each of such frequencies. Provision (24) is made for latching frequency shift data bit signals accordingly as output in a format identical to the frequency shift-keying RF format received. The receiver/decoder is especially useful for miniaturized transponder operation in which it alternates between receiving and transmitting modes, and is powered by capacitively stored charge in response to continuous transmission of the first frequency over a period.
