Abstract: A method is provided for equalizing OFDM symbol vectors received on AM in-band on-channel radio signal including a main carrier and first and second BPSK modulated subcarriers. The method comprises the steps of: computing a BPSK magnitude signal; filtering the BPSK magnitude signal; filtering complex samples received on the main carrier; using the filtered BPSK magnitude signal and the filtered complex samples received on the main carrier to compute a plurality of flat fade equalization coefficients; and multiplying the OFDM symbol vectors by the flat fade equalization coefficients. A receiver that includes an equalizer, which operates in accordance with the method is also provided.

Abstract: A method of tuning an antenna circuit includes: (a) receiving a signal on an antenna, (b) producing a received signal strength indication based on the received signal, (c) using the received signal strength indication to produce a control voltage, (d) using the control voltage to control a capacitance in an antenna matching circuit, (e) changing the control voltage to minimize a ratio of a change in the received signal strength indication to a change in the control voltage and (f) repeating steps (a), (b), (c), (d) and (e). An apparatus that implements the method is also provided.

Abstract: This invention provides a method of detecting time alignment of an analog audio signal and a digital audio signal in a hybrid radio system. The method comprises the steps of filtering the analog audio signal to produce a filtered analog audio signal, filtering the digital audio signal to produce a filtered digital audio signal, and using the filtered analog audio signal and the filtered digital audio signal to calculate a plurality of correlation coefficients, wherein the correlation coefficients are representative of time alignment between the analog audio signal and the digital audio signal. An apparatus for performing the method is also provided.

Abstract: An apparatus includes first and second speakers, and an antenna including a first pair of wires connected to the first speaker, a second pair of wires connected to the second speaker, and a conductive sleeve surrounding portions of the first and second pairs of wires, the sleeve forming a coaxial capacitor with the first and second pairs of wires. The apparatus can further include an inductor connected between the first and second pairs of wires and the sleeve, to form a resonant circuit with the coaxial capacitor.

Abstract: A method for detecting a digital radio signal includes the steps of receiving the digital radio signal including a series of symbols, developing a correlation waveform having a peak that corresponds to a symbol boundary, normalizing the correlation waveform, and calculating a peak value of the normalized correlation waveform, wherein the peak value represents the quality of the received digital radio signal. A receiver that performs the method is also provided.

Abstract: A method for detecting a digital radio signal includes the steps of receiving the digital radio signal, developing a correlation waveform having a peak that corresponds to a symbol boundary, normalizing the correlation waveform, calculating a peak value of the normalized correlation waveform, and dwelling on the received digital radio signal when the peak value exceeds a predetermined threshold. A receiver that performs the method is also provided.

Abstract: A method of broadcasting an AM compatible digital audio broadcasting signal includes: producing an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal, producing a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation (CPTCM) including a code mapped to overlapping partitions including an upper main partition, a lower main partition, an upper backup partition and a lower backup partition, and a non-overlapping tertiary partition, and transmitting the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals. Transmitters that broadcast the signal and receivers that receive the signal, and the reception method are also included.

Abstract: A method is provided for equalizing OFDM symbol vectors received on AM in-band on-channel radio signal including a main carrier and first and second BPSK modulated subcarriers. The method comprises the steps of: computing a BPSK magnitude signal; filtering the BPSK magnitude signal; filtering complex samples received on the main carrier; using the filtered BPSK magnitude signal and the filtered complex samples received on the main carrier to compute a plurality of flat fade equalization coefficients; and multiplying the OFDM symbol vectors by the flat fade equalization coefficients. A receiver that includes an equalizer, which operates in accordance with the method is also provided.

Abstract: A method of tuning an antenna circuit includes: (a) receiving a signal on an antenna, (b) producing a received signal strength indication based on the received signal, (c) using the received signal strength indication to produce a control voltage, (d) using the control voltage to control a capacitance in an antenna matching circuit, (e) changing the control voltage to minimize a ratio of a change in the received signal strength indication to a change in the control voltage and (f) repeating steps (a), (b), (c), (d) and (e). An apparatus that implements the method is also provided.

Abstract: A method for symbol tracking in AM in-band on-channel radio receivers comprises the steps of: receiving a stream of time domain samples; assembling a set of the time domain samples equal to a symbol time plus a half symbol delay in response to a symbol timing adjustment value for each symbol period; interpolating the time domain samples; partitioning the interpolated time domain samples into a first group of samples representing half-off symbols and a second group of samples representing on-time symbols; processing the first and second groups of samples to produce the symbol timing adjustment value; and outputting the second group of samples representing on-time symbols at a symbol rate. An apparatus that performs the method is also included.

Abstract: A method of broadcasting an AM compatible digital audio broadcasting signal includes: producing an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal, producing a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation (CPTCM) including a code mapped to overlapping partitions including an upper main partition, a lower main partition, an upper backup partition and a lower backup partition, and a non-overlapping tertiary partition, and transmitting the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals. Transmitters that broadcast the signal and receivers that receive the signal, and the reception method are also included.

Abstract: A transmitter for broadcasting an AM compatible digital audio broadcasting signal includes an analog modulator for producing an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal, and a digital modulator for producing a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation including a code mapped to overlapping partitions. In a first operating mode the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals are in a 20 kHz channel and in a second operating mode the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals are in a 30 kHz channel.

Abstract: A method for carrier tracking in AM in-band on-channel radio receivers comprises the steps of receiving an input signal, generating a local oscillator signal in response to an oscillator control signal, mixing the input signal with a local oscillator signal to produce a first signal, filtering the first signal to produce a filtered first signal at a decimated sample rate, detecting the phase error and frequency error of the filtered first signal normalized to mitigate effects of signal fades, and using an adaptive loop filter to produce the oscillator control signal in response to the phase error and frequency error of the filtered first signal. An apparatus that performs the method is also provided.

Abstract: A method is provided for equalizing OFDM symbol vectors received on AM in-band on-channel radio signal including a main carrier and first and second BPSK modulated subcarriers. The method comprises the steps of: computing a BPSK magnitude signal; filtering the BPSK magnitude signal; filtering complex samples received on the main carrier; using the filtered BPSK magnitude signal and the filtered complex samples received on the main carrier to compute a plurality of flat fade equalization coefficients; and multiplying the OFDM symbol vectors by the flat fade equalization coefficients. A receiver that includes an equalizer, which operates in accordance with the method is also provided.

Abstract: A method of broadcasting an AM compatible digital audio broadcasting signal includes: producing an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal, producing a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation (CPTCM) including a code mapped to overlapping partitions including an upper main partition, a lower main partition, an upper backup partition and a lower backup partition, and a non-overlapping tertiary partition, and transmitting the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals. Transmitters that broadcast the signal and receivers that receive the signal, and the reception method are also included.

Abstract: A method of transmitting digital audio broadcasting signals comprises the steps of generating a plurality of output frames of information to be transmitted, wherein each of the output frames includes a plurality of blocks of data and each of the output frames is synchronized with an absolute time reference, and transmitting the output frames to a plurality of receivers. Transmitters that broadcast in accordance with the method and receivers that receive the transmitted signal are also disclosed. A method is also provided for receiving digital audio broadcasting signals comprising the steps of receiving a digital audio broadcasting signal comprising a plurality of output frames of information, wherein each of the output frames includes a plurality of blocks of data and each of the output frames is synchronized with an absolute time reference, and determining the start of each output frame relative to an absolute time reference.

Abstract: A method of reducing peak-to-average power ratio in an OFDM signal comprises the steps of modulating a set of subcarriers with a set of data symbol vectors to produce a first modulated signal, limiting the magnitude of the first modulated signal to produce a first limited modulated signal, demodulating the first limited modulated signal to recover distorted input symbol vectors, constraining the distorted input symbol vectors to values greater than or equal to a minimum threshold value to produce constrained data symbol vectors, constraining out-of-band spectral components to lie within a predetermined mask, and remodulating the constrained data symbol vectors. A transmitter that performs the method is also included.

Abstract: A method for synchronizing an exciter clock with a modem frame clock in a broadcasting system comprises the steps of receiving a plurality of modem frame pulses that are representative of the start of modem frames of audio signals and data signals, wherein timing of the modem frame pulses is controlled by a modem frame clock, producing an exciter clock signal, counting pulses representative of the exciter clock signal to produce a count representative of timing error of each incoming modem frame pulse, and controlling the exciter clock signal in response to the count. An apparatus that performs the method is also provided.

Abstract: An apparatus includes first and second speakers, and an antenna including a first pair of wires connected to the first speaker, a second pair of wires connected to the second speaker, and a conductive sleeve surrounding portions of the first and second pairs of wires, the sleeve forming a coaxial capacitor with the first and second pairs of wires. The apparatus can further include an inductor connected between the first and second pairs of wires and the sleeve, to form a resonant circuit with the coaxial capacitor.

Abstract: A method of processing a baseband multiplex signal comprises the steps of frequency modulating the baseband multiplex signal to produce a first modulated signal, filtering the first modulated signal to produce a first filtered signal, demodulating the filtered signal to produce a demodulated baseband multiplex signal, correcting the demodulated baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the demodulated baseband multiplex signal to produce a corrected signal, and frequency modulating the corrected signal to produce a second modulated signal. An apparatus that operates in accordance with the method is also provided.