The present invention provides a technique and system for modifying the modulation of the 66.5 kHz subcarrier in such a way that its spectrum will not overlap that required by the 57 kHz subcarrier, while at the same time maintaining compatibility with existing subcarrier receivers. A special signal is created whose spectral shape is asymmetrical with respect to the 66.5 kHz subcarrier. In the frequency domain, the lowest frequency part of the symmetrical spectrum is cut off, flipped about the carrier frequency and then added to the highest frequency part of the spectrum. This technique and system takes advantage of the fact that the receiver, with which the system is designed to operate, uses a sampling process which products frequency aliasing. With the present invention, the spectral shape produced at the transmitter is such that the aliasing caused by sampling in the receiver results in the lower-than-carrier and higher-than-carrier portions of the spectrum being adding together, producing in the receiver a symmetrical spectrum.
A receiver is provided capable of receiving both RDS (Radio Data System) and DARC (DAta Radio Channel) system FM multiplex broadcasting. An RDS signal demodulating circuit is provided with a PLL circuit which comprising a first frequency divider for dividing an output of a crystal oscillator, a phase comparator for inputting an output of the first frequency divider, a low-pass filter connected with the phase comparator, a VCO connected with the low-pass filter, and a second frequency divider for dividing an output of the VOC and outputting the divided output signal to the phase comparator. An output of the VCO is transmitted as a reference clock RDSCL for demodulation of an RDS signal.
A tuning system and a tuning method in a broadcast signal receiver, in which a radio frequency (RF) spectrum signal adopting an inverting method is filtered by an asymmetric bandpass filter of a tuner to improve the receiving sensitivity. This tuning system includes a first mixer, a filter and a second mixer. The first mixer mixes a predetermined oscillation frequency with an inverted 8 VSB digital broadcast signal in the idle space between upper and lower normal NTSC broadcast signals of high frequency band received from a transmitter, transfers the upper NTSC broadcast signal to the lower side and the lower NTSC broadcast signal to the upper side, inverts the transferred NTSC broadcast signals, and changes the state of the 8 VSB digital broadcast signal into a normal state. The filter attenuates the inverted upper and lower NTSC broadcast signals output from the first mixer to a predetermined band and amplifies the normal 8 VSB digital broadcast signal into a predetermined band. The second mixer mixes a predetermined oscillation frequency with the attenuated NTSC broadcast signals and the amplified 8 VSB digital broadcast signal output from the filter and lowers the frequency of the mixed signal to a predetermined frequency band. Accordingly, an RF spectrum transmission method is changed from a normal method to an inverting method, so that the DTV interference of adjacent NTSC signals is minimized.
A frequency processing circuit has a suppressing circuit for suppressing a lower sideband wave of an input FM signal whose frequency is modulated, a frequency conversion circuit for converting the frequency of an output of the suppressing circuit, and an emphasizing circuit for emphasizing a lower sideband wave of an output of the frequency conversion circuit. The emphasizing circuit emphasizes a share of the amount of the wave suppressed by the suppressing circuit.
Selectable receiver addressing is used to control how messages are output from different receivers. Users selectively enable and disable personal addresses in the receiver. The receiver polls time slots where the data for enabled addresses may be transmitted. Enabled addresses are compared with transmitted receiver addresses. If the transmitted address matches one of the enabled receiver addresses, the message is output to the receiver user. If the transmitted address does not match the receiver address, the message is not processed and, accordingly, the receiver operator is not disturbed.
Pager data is transmitted at different subcarrier frequencies on different FM broadcast channels. The subcarrier frequency of the pager data is selected to avoid conflicts with signals transmitted from other systems. The pager receiver decodes data at any one of the multiple subcarrier frequencies according to the active subcarrier used on the currently tuned broadcast channel. In one embodiment, the subcarrier frequency of the pager data is contained in control packets of a time division multiplexed data frame. The receiver decodes the control packets to determine which broadcast frequencies and associated subcarrier frequencies contain potential pager signals. The receiver accordingly searches the identified broadcast frequency and automatically reconfigures a circuit demodulator to decode data packets at the identified subcarrier frequencies.