摘要:
A wristwatch paging receiver is provided with an antenna matching network that automatically retunes the network at the beginning of a listening interval. During the retuning operation, a control signal is applied to a variable tuning element in the matching network, such as a varactor diode, and is swept from a minimum value to a maximum value. This sweeping is desirably performed in discrete voltage steps that correspond to unit increments of varactor capacitance. A feedback signal from the receiver, such as an AGC signal, is monitored during this operation to note which varactor bias signal yields the maximum AGC signal. After the sweep is concluded, the apparatus applies to the varactor the bias voltage that yielded the maximum AGC signal during the sweeping operation. This bias voltage is maintained through the end of the listening interval. At the beginning of the next listening interval, the process may be repeated.
摘要:
An FM receiver is self tested by connecting a positive feedback network in circuit with a wideband, front end r.f. amplifier of the receiver, so that the amplifier is converted into an oscillator. R.f. and i.f. characteristics of the receiver are determined by comparing the amplitude of an i.f. signal with a predetermined reference value while the amplifier is converted to an oscillator. Noise characteristics of the receiver are determined by comparing the amplitude of an audio frequency signal of the receiver with a predetermined value while the amplifier is converted to an oscillator and the amplifier derives an unmodulated r.f. output. Baseband characteristics of the receiver are determined by varying a reactance in the positive feedback path to impose FM on r.f. oscillations derived by the amplifier and by comparing the amplitude of the output of the audio frequency amplifier with a predetermined value. By varying the value of the reactance in the feedback loop, the oscillating frequency is swept to determine the center operating frequency and i.f. bandwidth of the r.f., amplifier.
摘要:
A device for generating a tuning frequency set command signal for a tuner system having a manual tuning mode and an automatic channel scanning mode, including a manually operable means for generating an up control signal for raising the tuning frequency and a manually operable means for generating a down control signal for lowering the tuning frequency, and timing means for measuring the duration of the up or down control signal, and control means for automatically selecting the automatic channel scanning mode when the duration of the up or down control signal becomes longer than a predetermined time period, is characterized by a reset means for resetting the timing means each time when the up or down control signal disappears, thereby alleviating the fear that the automatic channel scanning mode is erroneously selected when the means for generating up or down control signal is operated more than one time within the predetermined time period.
摘要:
A signal-seeking tuning system for a television receiver scans the VHF and UHF signal bands until a present TV channel signal is detected. Tuning voltage is developed by a digital-to-analog converter in response to a binary word stored in an up/down counter. The value of the binary word increases when a scan-up signal is applied and decreases when a scan-down signal is applied. Band signals are automatically sequenced to the next higher frequency band when the binary word "rolls-over" from a maximum to a minimum value, or to the next lower frequency band when the binary word rolls-over from its minimum to its maximum value. Scanning is stopped by inhibiting changing of the binary word when a valid sequence of AFT signals is detected.Thereafter, the tuning voltage is compensated for drifts by incrementing or decrementing the binary word whenever the AFT signal departs from a predetermined condition. This correction is inhibited, however, when the binary word is at its minimum or maximum value so that unwanted bandswitching is avoided.
摘要:
A search tuning type channel detector system for television receivers. When AFC voltage of a tuner has attained a first predetermined voltage level, frequency sweeping direction for tuning is reversed and stopped thereby to tune the tuner at an optimum tuning frequency. Means are provided to allow the inversion as well as stoppage of the frequency sweeping only when AFC voltage has attained a second predetermined voltage level, thereby to exclude possible erroneous operation due to noise or the like spurious signal components.
摘要:
There is disclosed an electronic selection apparatus comprising a surface acoustic wave comb filter, in which the local oscillator frequency of an electronic tuner is swept up to a frequency higher than a peak frequency of the surface acoustic comb filter corresponding to a desired channel number (an upward direction), and then swept toward the opposite direction (a downward direction) until a predetermined number of peaks of the comb filter is counted while checking the presence of an AFC signal, whereby an erroneous tuning operation may be prevented, provided that the signal of the desired channel is present within a predetermined range in the vicinity of the receiving frequency of the desired channel.
摘要:
An automatic tuning scheme for use in TV receivers includes a start/stop circuit which creates a search start signal and a search stop signal upon the receipt of a search start instruction and a detected incoming signal, respectively, a tuning voltage generator which generates a gradually varying tuning voltage under control of the search start signal and search stop signal, and a memory circuit for storing the tuning voltage from the generator when desired. The tuning voltage stored in the memory circuit is supplied to a tuner including a well known voltage-sensitive capacitance diode.
摘要:
An automatic TV tuner circuit responsive to a tuning voltage for tuning over a desired frequency reception range. The tuning voltage is generated by a staircase voltage generator. A discriminator produces an output signal having a nominal value when the receiver is tuned to a transmitted broadcast frequency and at a discriminator output having a predetermined difference from the nominal value, a sequence control circuit halts the operation of the staircase generator and regulates the tuning voltage in a continuous manner under control of the discriminator output signal to complete the tuning process.
摘要:
A channel selection apparatus of the scanning tuning type in which a tuning frequency is swept by a sweeping voltage to select a given tuning frequency. The sweep of the frequency is controlled for each channel by a control signal stored for each channel in the form of a number of pulses to attain exact instant tuning to a specified channel. An operating unit which compensates for temperature drift of the elements comprising the apparatus is provided to correctly compensate for temperature drift of these elements thereby attaining exact tuning.
摘要:
A tuning system for digitally controlled electronically tuned tuner with automatic fine tuning (AFT) constantly operable to hold the tuner at a predetermined optimum frequency setting, especially a television channel. A reversible counter provides the digital signal to control the tuning of the tuner and is, itself, deliberately shifted from one setting to another by pulses from a source, such pulses being applied to the UP input terminal of the counter as the up-tuning pulses to shift the tuner frequency higher. Pulses from the same source are also used as down-tuning pulses when applied to the DOWN input terminal of the tuning pulses to a lower frequency supplied to two AFT AND circuits. One output logic up-tuning instruction signal E.sub.U of the AFT circuit enables the up-tuning AFT AND circuit only in a certain sub-range below the desired frequency. The other output logic down-tuning instruction signal E.sub.D of the AFT circuit enables the other AFT AND circuit only in a certain sub-range above the desired frequency. Consequently, deliberate application of up-or-down-tuning pulses to the UP or DOWN terminals changes the count as desired, being only partially counteracted by the lower frequency, AFT-controlled pulses to the opposite counter terminal.