Abstract: The number of oscillators required to construct a digital radiocommunication terminal can be reduced and a circuit used for the digital radiocommunication terminal can be reduced in size. For this purpose, the digital radiocommunication terminal for effecting information transmission using an N (integer)-phase-shift-keyed signal (identification symbol number N=4 upon .pi./4 shifted QPSK modulation), is constructed such that an oscillation frequency generated from a reference oscillator employed with a frequency synthesizer is selected to have a common multiple of a second intermediate frequency and an identification symbol phase N and is supplied to a detector for outputting received data therefrom.

Abstract: A FM (Frequency Modulated) DCFB (Deviation Compression Feedback) signal demodulator can be achieved by utilizing FM deviation compression feedback techniques. An FM signal is coupled to a mixer (10) wherein a signal from a local oscillator is mixed with the input signal. The output of the mixer is then coupled to a variable selective IF amplifier. The IF amplifier couples the signal to a limiter amplifier, the output of the limiter amplifier is FM demodulated and fed to an output. The output signal is simultaneously fed back through a variable Frequency Compensation Network (FCN) (Loop Filter). The output signal of the FCN is then fed back to a local oscillator (17). The output of the local oscillator (17) is in turn fed back into the original mixer (10). The improved demodulated signal is sampled at an output (26).

Abstract: A receiver and a method of setting the frequency of the reference signal in the receiver, the receiver comprising a voltage controlled crystal oscillator which provides the reference frequency for a synthesizer. The synthesizer in turn produces the local oscillator frequency signal in the receiver. Temperature fluctuations in the crystal are compensated for by microprocessor control of the oscillator. The reference frequency is accurately set by incrementaly scanning the signal channel until a signal of magnitude greater than a predetermined level is detected, whereupon the receiver locks onto said detected signal and instructs the oscillator to produce a reference frequency signal of a certain frequency according to the frequency of said detected signal.

Abstract: In a radio receiver a PLL oscillator generates a phase locked oscillation signal with a controllable frequency and a frequency multiplier multiplies the controllable frequency with a controllable factor into a local oscillation frequency to provide a local oscillation signal for mixing into an IF signal with a radio signal reaching the receiver, the IF signal is monitored to raise the controllable frequency and to reduce the controllable factor when a spurious signal coexists with the radio signal. This coexistence is detected by monitoring a level difference between the IF signal and an output signal of an IF filter. Preferably, the oscillator comprises in a PLL two VCO's for generating phase locked oscillation signals of higher and lower oscillation frequencies, such as 260 and 65 MHz, and a controllable prescaler supplied with high and low voltage signals when the VCO's are put in operation at the higher and the lower oscillation frequencies.

Abstract: A peak and valley measuring circuit (40) featuring a single digital-to-analog converter (DAC) (100), a peak counter (110), a valley counter (120), and a comparator (130). The peak and valley measuring circuit (40) uses the peak counter (110) when detecting peaks of the recovered audio signal and the valley counter (120) when detecting valleys of the recovered audio signal. The DAC (100) is used in conjunction with one of the counters (110) or (120) depending on whether peaks or valleys are being detected, and is preferably a current-mode DAC.

Abstract: In a radio receiver for receiving a radio signal, a counter (32) counts an eventual intermediate frequency of an amplified signal based on a reference signal as a count datum. A frequency controller (27) controls a reference frequency of the reference signal according to the count datum. A reference oscillator (25) is controlled by the frequency controller to produce the reference signal. Receiving a radio signal by double superheterodyne, the radio receiver gives the eventual intermediate frequency to the amplified signal. In the amplified signal, the frequency controller suppresses an eventual frequency drift which results from frequency drifts of a first local oscillation and a second local oscillation. The radio receiver may be a single superheterodyne receiver.

Abstract: A television receiver having an electronically controlled tuner is presented. A controlled local oscillator provides a local oscillator signal for the mixer. The controlled local oscillator includes an first input terminal for receiving a control signal for controlling its frequency and a first output terminal for providing an output local oscillator signal. A phase-locked loop includes a second input terminal for receiving the local oscillator signal and a second output terminal for providing a signal back to the first input terminal of the controlled local oscillator for controlling its frequency. At least a portion of the coupling between the first output terminal and the second input terminal, and the second output terminal and the first input terminal, have a common line.

Abstract: The PLL circuit provides both the advantages of analog phase control, in which a good C/N ratio can be realized, and the advantages of digital phase control, in which broad-band lock can be performed. A multi-channel FM receiving method and apparatus are able to utilize the PLL circuit to reduce the influence of the leakage occurring among input signals and suppress image disturbance.

Abstract: An automatic frequency control circuit mounted on a mobile station in mobile communication. The automatic frequency control circuit performs feedback control of an oscillation frequency of a local oscillator used in conversion of a reception frequency to an intermediate frequency signal in response to the count result of the frequency of the intermediate frequency signal. If a receiver is not in the hand-off state, counting is performed for comparatively long time; if in the hand-off state, counting is performed for comparatively short time conforming to required stabilization performance at hand off. Occurrence of variations in count values caused by fading is detected, and only the count values worthy of trust are used as a base of control. A level drop caused by fading is compensated by self-oscillation.

Abstract: An apparatus and method for automatically controlling a reference frequency (120) in a receiver (104) that receives either analog (116) or digital (136) information signals. The receiver (18) includes a frequency translator (109) for translating a carrier frequency (137) to an intermediate frequency (118) and maintaining the intermediate frequency (118) at a desired value responsive to the reference frequency (120). A first measure of frequency error (211, 212) is detected between the reference frequency (120) and the intermediate frequency (118). A second measure of frequency error (125, 126) is detected between the reference frequency (120) and the intermediate frequency (118). A current signal (213) is produced responsive to the first measure of frequency error (211, 212) when the receiver receives the analog information signal (116) and responsive to the second measure of frequency error (125, 126) when receiver receives the digital information signal (136).

Abstract: A superheterodyne receiver has a receiver circuit formed into a single semiconductor chip comprising a pseudo band-pass filter employing components equivalent to those of an intermediate-frequency filter of the receiver circuit and an oscillation circuit employing the pseudo band-pass filter as a feedback path thereof.The oscillation circuit oscillates at a frequency equal in value to the center frequency of the intermediate-frequency filter. The semiconductor chip is further equipped with a PLL circuit allowing the frequency-division ratio of a variable frequency-divider circuit to be varied in order to control a reception frequency, and the oscillation frequency of the oscillation circuit is monitored. Data representing the reception frequency is derived from the monitored oscillation frequency and the value of the frequency-division ratio of the variable frequency-divider circuit, and then output to a display element to display the reception frequency.

Abstract: According to this invention, an SAW electric part includes an SAW filter and an SAW oscillator formed on a substrate having the same temperature characteristics as those of a substrate on which the SAW filter is formed. A frequency converter includes the SAW electric part, a second local oscillation circuit, a frequency converter, a first mixer, and a second mixer. The second local oscillation circuit oscillates a second local oscillation signal using the SAW oscillator. The frequency converter converts a frequency of the second local oscillation signal to generate a first local oscillation signal. The first mixer mixes the first local oscillation signal with an input signal to output a composite signal to the SAW filter. The second mixer mixes an output from the SAW filter with the second local oscillation signal to output a frequency conversion signal.

Abstract: A double conversion frequency converter includes first and second mixing stages. The first mixing stage includes a first programable Local Oscillator (LO) synthesizer and a first mixer, and the second mixing stage includes a second programable LO synthesizer and a second mixer. The first and second LO synthesizers have a wide band tuning range for receiving a separate predetermined reference signal and generating therefrom first and second LO output signals, respectively, which each are changeable by predetermined large frequency steps. The first mixer mixes an input signal to the frequency converter with the first LO output signal for generating a first predetermined mixer output signal. The second mixer mixes a predetermined sideband generated in the first predetermined mixer output signal with the second LO output signal for generating a second predetermined mixer output signal which is use for the output signal for the frequency converter.

Abstract: A frequency converter circuit which includes a first frequency conversion unit which mixes a received signal and a first local oscillation signal to produce a first intermediate frequency signal and a second frequency conversion unit which mixes the first intermediate frequency signal and a second local oscillation signal to produce a second intermediate frequency signal. Here, the first frequency deviation included in the first local oscillation signal and the second frequency deviation included in the second local oscillation signal are combined and applied to the reference oscillation unit. The oscillation frequency of the reference oscillation unit is subjected to feedback control so that the combined frequency deviation becomes zero. This feedback is formed so that a first and second local oscillation signals are produced based on reference signals obtained by dividing a reference signal having the oscillation frequency by a first dividing ratio and a second dividing ratio.

Abstract: A quadrant generator for generating a pair of pulse trains maintained in perfect phase quadrant with one another. The quadrature generator includes a feedback control loop for altering the duty cycle of an oscillating signal applied to a master-slave flip-flop pair configured to generate a pair of pulse trains maintained in a relative phase relationship. The feedback control loop controls the duty cycle of the oscillating signal applied to the master-slave flip-flop pair which, in turn, is determinative of the phase relationship between the pulse train pair generated by the master-slave flip-flop pair. When the pulse trains generated by the flip-flop pair are beyond phase quadrature, a control signal generated by the feedback control loop alters the duty cycle of the oscillating signal applied to the flip-flop pair to alter the phase relationship between the pulse trains of the pulse train pair.

Abstract: A superheterodyne receiver comprises a variable frequency oscillator of PLL (phase-locked loop) type for implementing a first local oscillator and a variable frequency oscillator not of PLL type for implementing a second local oscillator. At least the frequency of a first locally generated signal is varied at reception to vary a received frequency, the frequency of the first locally generated signal is set at frequency calibration to a level equal to the frequency of a first intermediate-frequency signal, the second intermediate-frequency signal is frequency-converted by a BFO signal to a signal having a frequency of voice band, and the frequency of a second locally generated signal is calibrated to set the frequency of the frequency-converted signal to a specified level.

Abstract: A double super-heterodyne tuner provided with an up-converting section and a down-converting section, and including an input filter constituted by single tuning to be supplied with an input signal, an RF amplifier for amplifying the signal passing through the input filter, and an inter-stage tuning circuit constituted by single tuning connected to an output end of the RF amplifier and provided at an input portion of the up-converting section. The input filter and the inter-stage tuning circuit are supplied with a tuning voltage different from that supplied to a first local oscillator so as to alter its filter characteristics for simplification of the circuit construction and improvement of NF (noise factor).

Abstract: The present invention relates to a radio receiver for receiving a radio signal, a first circuit for beating the signal to zero intermediate frequency in phase and quadrature shifted signals, a circuit for amplifying the in phase and quadrature shifted zero intermediate frequency signals, a second circuit for beating the amplified intermediate frequency signals to predetermined non-zero intermediate frequency in phase and quadrature shifted signals, a summer for summing the non-zero signals, and a circuit for applying the summed signals to a discriminator to obtain an output signal. Other embodiments are extended POCSAG for enhanced battery saving, paging sequence numbers for reception integrity control, digital AFC, script control of the pager for organizer/schedule applications, a vibrator holster for improved pager format and saving of battery power, intelligent low battery detection, and features arising from electronic on/off function.

Abstract: A radio receiver for use with a time slot paging system which receives intermittent data includes a direct coupled zero IF receiver circuit with at least one automatic gain control (AGC) amplifier stage. DC offset errors are removed from the AGC amplifier stages by a timed zero adjustment circuit that is switched into the AGC circuit just prior to the receipt of data. The resulting zero IF circuit may be miniaturized in monolithic form making it ideal for use in a wristwatch sized pager.

Abstract: A frequency modulation (FM) stereo broadcast receiver detects the onset of multipath interference and initiates corrective action to minimize the audible effects of multipath. Under an unacceptable multipath interference condition, a multipath detection signal disables the FM RF mixer thereby preventing any further energy in the multipath event from entering succeeding sections of the receiver. This action reduces noise generated by multipath interference and allows the output to return to normal in a shorter time. In another aspect of the invention, a phase-locked loop employed in a stereo decoder circuit is latched during the multipath disturbance in order to avoid rapid changes in the phase of the regenerated pilot employed in the stereo decoder.

Abstract: A receiver having an RF section, a mixer stage and a signal processing stage, the mixer stage receiving a mixing frequency from a frequency synthesis circuit which includes a phase-locked loop provided with a phase detection device having a current output, a loop filter including a .pi.-shaped RC network having an input shunt path and an output shunt path which are connected to respective ends of a series resistor incorporated in a series path, and to ground, and include first and second capacitances, respectively, and with a voltage-controlled oscillator, a reference frequency being applied to the phase detection device.

Abstract: An electronic apparatus includes at least a receiver having a synthesizer section for selecting a receiving frequency and providing an information signal corresponding to the selected receiving frequency, a microcomputer operating on a clock signal for controlling the synthesizer section, and a circuit responsive to the information signal for shifting the clock frequency when the selected receiving frequency is a frequency disturbed by a higher harmonic of the clock frequency, thereby to avoid disturbance of reception of the broadcast signal without requiring undue reduction of the clock frequency.

Abstract: A heterodyning lock-in amplifier in which the reference signal is shifted up in frequency (as in prior art designs), but then shifted back down in frequency prior to mixing with the input signal.

Abstract: Both the low and high intermediate frequencies (IF) are amplified simultaneously in a single IF amplifier strip. For proper operation it is required that the two IFs be sufficiently isolated from each other so that independent tuning can be achieved. In operation, the RF signal is amplified and mixed down by a first local oscillator (LO). The RF signal is amplified in the IF strip to obtain IF #1. IF #1 from the strip is mixed down with a second LO in a feedback arrangement to obtain IF #2 simultaneously with IF #1 from the strip.

Abstract: A first control circuit is provided with a temperature detector and a memory in which temperature related control data is stored. The control circuit outputs a control signal, which varies with ambient temperature, to a local oscillator which is connected with a mixer. The mixer receives an incoming radio frequency signal and a local frequency signal from the local oscillator and outputs an IF signal. The local oscillator is controlled in a manner wherein the frequency of the IF signal parallels the temperature dependent shift in center frequency of a surface acoustic wave type IF filter. The IF signal is applied to a second mixer to which a second control circuit is coupled. The second control circuit maintains the output of the second mixer at a predetermined value to compensate for the first IF's frequency shift caused by the first control circuit.

Abstract: A TV signal receiving system, in order to tune a broadcasting frequency of a desired channel after receiving a TV signal, converts the TV signal into an intermediate frequency having a frequency higher than the maximum frequency in a TV broadcasting frequency band and then converts again the frequency of the signal into another intermediate frequency in conventional TV systems so as to improve the rejection characteristics of image and IF signals. The system comprises a first converter for tracking a desired channel frequency from a TV RF signal and converting the frequency into a first IF of 2 GHz, a band-pass filter of the 2 GHz IF for filtering only the first IF frequency signal in the first converter, and a second converter for converting the filtered first IF into 45 MHz of the conventional TV IF.

Abstract: A tuner station apparatus includes a first mixer for combining an input signal and a first local oscillation signal, and a second mixer for combining an output of the first mixer and a second local oscillation signal. The first and second local oscillation signals are generated by first and second PLL circuits, respectively. Each of the first and second PLL circuits include a frequency divider, a variable frequency divider, a phase comparator, a low pass filter, and a voltage controlled oscillator. The frequency divider of the first PLL circuit has a higher frequency division ratio than that of the second PLL circuit.

Abstract: A second IF signal is counted either directly or indirectly. An AFC operation is performed based on the counting result. A plurality of count periods (A1, C1) are provided within a video signal period (Y+H) including a horizontal blanking period, and the plurality of count periods (A1, C1) are randomly shifted for each field. An AFC operation is performed based on a plurality of counting results in a plurality of field periods which correspond to one cycle of an energy diffusion signal.

Abstract: A D.C. modulated phase locked oscillator (220 or 264) is usable separately to provide an output that is both phase locked and D.C. modulated or is usable in a radio frequency receiver (200). The D.C. modulated phase locked oscillator (220or 264) includes a phase locking oscillator (222 or 266) and a D.C. modulator (224 or 268). Both a forward path (14) and a feedback path (16) are D.C. modulated. In one embodiment. D.C. modulation of the feedback path (16) includes using a modulation oscillator (64) and two flip-flops (228 and 164) to develop quadrature square waves, and using a quadrature phase shift keying (QPSK) mixer (234) to subtract a frequency of one of the square waves from the frequency in the feedback path (16). In another embodiment, D.C.

Abstract: A Doppler compensating device which conserves power and can be used with hand-held communication devices comprises a phase lock loop for tracking a Doppler phase offset and a Doppler offset calibration loop which generates a Doppler offset curve. The Doppler offset calibration loop extracts Doppler offset points from the phase lock loop, and from these points calibrates a set of three parameters defining the Doppler offset curve using an estimation algorithm such as the least squares algorithm. After the curve is defined, the compensation device extracts points from the Doppler offset curve and deactivates the phase lock loop. This process preserves power within the hand-held communication devices.

Abstract: A method and apparatus is disclosed for automatic elimination of frequency instabilities in a receiver frequency converter. Such instabilities result from temperature variations and mechanical vibrations of the local oscillator of a first stage converter. A marker signal is introduced into the first stage down converter mixer and is subjected to the same variations in frequency conversion as is the received signal from an antenna. Intermediate down converted received signals and an intermediate down converted marker signal are received by a second stage converter where such signals are applied to a mixer, the output of which is free of frequency variations introduced by the local oscillator of the first stage converter.

Abstract: A direct conversion FM receiver that comprises a quadrature mixer, an A to D converter, a digital demodulator, a digital phase lock loop, and frequency offset setting means is disclosed. The quadrature mixer receives FM signals and mixes them with a local oscillator signal to produce an analog in-phase baseband signal and an analog quadrature baseband signal. The analog in-phase baseband signal and the analog quadrature baseband signal are converted into digital signals by the A to D converter. The digitally converted baseband and quadrature signals are digitally demodulated and filtered by the digital demodulator such that modulation information is produced. The modulation information is used, at least in part, to control the phase lock loop means.

Abstract: An FM detection system receives an FM input signal containing a plurality of carrier bands, including a tuned carrier band. The tuned carrier band is separated from side carrier bands by a frequency guard band. A detected, demodulated output signal is fed back to at least one local oscillator, which generates corresponding local FM signals having a deviation which is in phase with the deviation of the tuned carried. The FM input signal and the local FM signal are inputs to a guard band expansion device. The guard band expansion device includes a harmonics generator which produces an output spectrum which is a multiple of its input spectrum. In one embodiment, the harmonics generator operates directly on the FM input signal, its output signal then being beat by a mixer with the local FM signal. In another embodiment, the operations of harmonics generation and mixing are reversed.

Abstract: A receiver utilizing a plurality of small paraboloid antennas in lieu of a single large antenna of equal area, each antenna connected to a separate phase coherent heterodyne receiver channel includes a main channel and branch channels, the channels being summed to provide a carrier phase locked loop local oscillator signal that is distributed to all channels producing phase coherent IF signals in all the channels. These are summed to enhance the carrier margin or dB from the sensitivity threshold, of the system combining the receiver channels, to a level greater than that of the single antenna of equivalent area with its single receiver. The tendency toward cycle slipping near threshold is further reduced by providing summed additional amplified uncorrelated predetection receiver noise in the IFs of the branch receiver coupled to the main receiver.

Abstract: A direct conversion FM receiver that includes AC coupling and automatic gain control employs an offset frequency at the first local oscillator. The offset frequency prevents the frequency spectrum occupied by the signal modulation from being affected by AC coupling. The offset frequency is chosen so that it translates the frequency spectrum of the received signal outside the DC notch created in the spectrum by the AC coupling. To conserve battery supplied power, an error amplifier coupled between the output of the receiver and the first local oscillator maintains the offset frequency after it has been established by a frequency synthesizer, which is then turned off.

Abstract: A mobile station equipment for a mobile radio telephone system uses a voltage-controlled, temperature-compensated crystal oscillator (VC-TCXO) as a reference oscillator for local oscillators in frequency converters which convert an RF signal into IF signals. The oscillation frequency of the VC-TCXO is controlled by counting the second IF information and evaluating its difference from a certain reference value. At reception, the local oscillators have their reference frequency stabilized based on the stable frequency information from the base station. The equipment is compact and has reduced power dissipation and lower manufacturing cost.

Abstract: The tuner section of a communications receiver 10 includes a gallium arsenide voltage controlled oscillator 48 for upconverting the received signal in mixer 18. Phase noise and post tuning drift associated with oscillator 48 is impressed onto the signal supplied by a second oscillator network 46. Thus, the outputs of mixers 18 and 78 both contain noise and post tuning drift associated with the gallium arsenide oscillator 48. Mixer 28 is used to substract the noise and drift component on line 30 from that on line 32 to thereby provide an output 14 which is substantially free of the noise and drift associated with the efficient, but noisy gallium arsenide VCO 48.

Abstract: A dual branch receiver in which the frequency of the first local oscillator (32) is offset by a few hundred hertz from the input carrier in order to provide separate wanted and image components. Gain and phase control are provided to compensate for differences between the two branches (12, 14), the image signal being used to provide the required error signals. However in the event of the modulation frequency being equal to the offset frequency, the image signals cannot be distinguished from the wanted signals thus inhibiting gain and phase control. This drawback is overcome in the receiver in accordance with the present invention by wobbling the frequency provided by the first local oscillator (28). The wobbling frequency is preferably sub-audible so as not to be discernable to the ear.

Abstract: A muting control circuit is provided in which muting is performed when any one of a plurality of unlock detection signals is detected, indicating circuits is unlocked or when a data error is detected in a demodulator. In this way, reading time can be shortened to the minimum time required for muting. In addition, when one unlock detection circuit is triggered due to a disorder in the input, the unlock detection signal is provided immediately, so that the muting control signal is supplied and muting can be performed even when there is a time delay before the unlock detection circuit detects an unlocked state.

Abstract: A TVRO receiver for receiving frequency-modulated video signals, the receiver comprising a tuner including a superheterodyne circuit having a voltage-controlled oscillator (VCO), means for supplying a controlling input voltage to the VCO, and a mixer for combining incoming 1st IF signals with the output of the VCO to reduce the frequency of the 1st IF signals to a 2nd IF frequency which is sufficiently high to permit the output frequency of the VCO to be above the frequency range of the 1st IF signals, and a linear phase passband filter for passing a single video channel in the 2nd IF output from the mixer, the filter producing an output which is at least about 10 dB down from its peak at both +10 MHz and -10 MHz from the center of the passband of the filter.

Abstract: An FM receiver having a phase-locked loop demodulator and a control voltage correction circuit for the local tuning oscillator. The correction circuit includes a comparator for comparing the output frequency of the phase-locked loop demodulator with the output signal from a reference oscillator, the output of the comparator being connected through an integrator to provide a control signal for the local oscillator as part of an automatic frequency control loop. The comparator output is also fed through an integrator to an adder connected between the demodulator output and the demodulator oscillator controlled input, for setting the demodulator oscillator at the center intermediate frequency when no carrier signal is being received.

Abstract: An automatic fine tuning (AFT) circuit for a CATV receiver system of a double conversion type having a first local oscillator and a second local oscillator and a first mixer and a second mixer respectively supplied with oscillation outputs from the first and second local oscillators is disclosed. A reception signal is sequentially subjected to frequency conversation by use of the first and second mixers so as to attain an intermediate frequency signal of a predetermined value.

Abstract: In an RF receiver having a phase-locked loop demodulator and FLL tuning in its RF converter, the frequency of the VCO output signal in the phase-locked loop (PLL) demodulator is controlled indirectly by the FLL in the RF converter in response to a measurement of the VCO output signal in the phase-locked loop demodulator and comparison of such measured signal to a predetermined intermediated frequency. A microcomputer performs a refined FLL tuning algorithm to tune a selected RF carrier input signal and audio subcarrier input signals. The algorithm provides a means of assuring that the PLL demodulator is responding to an input signal derived from a carrier signal of a selected input frequency without having to use hardware to detect the presence of a carrier signal.

Abstract: Local frequency which is subject to fluctuate in a mobile subscriber set is locked to stable transmit frequency of a base station. A mobile subscriber set (FIG. 3) for angle modulated signal has a frequency mixer (3.6, 3.9), for converting wireless receive frequency to an intermediate frequency by using local frequency (F.sub.L1, F.sub.L2), a limiter (3.11) for limiting amplitude of intermediate frequency signal, a discriminator (3.12) for demodulating angle modulated signal, a standard oscillator (3.1) by using a quartz crystal oscillator and a synthesizer (64) for providing local frequency for said mixer (3.6), a digital frequency counter (3.14) for measuring intermediate frequency, and control means (3.16) for adjusting said standard oscillator (3.1) depending upon error of intermediate frequency measured by said counter (3.14).

Abstract: Apparatus for reducing the effects of mixer leakage in a zero IF transmission system includes first and second mixers having relatively equal leakage amounts from an oscillator port to an input port, with the input port of said first mixer adapted to receive a zero IF receiver input signal and with the output port of said first mixer capacitively coupled to the input port of the second mixer. The oscillator ports of the first and second mixers are coupled to a local oscillator output, with the output ports of said first and second mixers coupled respectively to an adder and subtractor circuit to provide respectively a DC signal indicative of the leakage and an output signal indicative of the magnitude of said input signal as effected by leakage to thereby enable the determination of said input signal after mixing.

Abstract: A method of reducing terrestrial interference is provided for a TVRO earth station receiver comprising a super-heterodyne circuit including a voltage-controlled oscillator (VCO), a mixer for combining incoming first IF signals with the output of the VCO to reduce the frequency of the first IF signals to a second IF range having a predetermined nominal center frequency, a pass band filter for filtering the second IF signals and having a pass band centered on the nominal second IF center frequency, and a microprocessor for controlling the input voltage to the VCO and for automatically setting the controlling input voltage at prescribed levels in response to a "channel select" command signal, so that the VCO produces an output frequency which centers the received signal for a selected channel on the nominal second IF center frequency.

Abstract: A TVRO receiver for receiving frequency-modulated video signals, the receiver comprising a tuner including a superheterodyne circuit having a voltage-controlled oscillator (VCO), means for supplying a controlling input voltage to the VCO, and a mixer for combining incoming 1st IF signals with the output of the VCO to reduce the frequency of the 1st IF signals to a 2nd IF frequency which is sufficiently high to permit the output frequency of the VCO to be above the frequency range of the 1st IF signals, and a linear phase passband filter for passing a single video channel in the 2nd IF output from the mixer, the filter producing an output which is at least about 10 dB down from its peak at both +10 MHz and -10 MHz from the center of the passband of the filter.

Abstract: A frequency converting circuit converts an input frequency into a desired frequency. To obtain the desired frequency, a first frequency converter converts the input frequency, by using an output frequency of a first local oscillator, into an intermediate frequency. The first local oscillator is a voltage controlled oscillator as a part of a phase locked loop circuit. A second frequency converter converts the intermediate frequency into the desired frequency by using an output frequency of a second local oscillator. A phase comparing circuit compares the phase of the output signal of the second frequency converter with that of the output signal of the first local oscillator. The phase comparing circuit is contained in the phase locked loop circuit. The result of the comparison is used for controlling the oscillating frequency of the first local oscillator.

Abstract: A demodulator of the type employed in a "zero-IF" system uses a local oscillator for providing quadrature output signals at the center frequency of a received signal to be demodulated. The demodulator has first and second mixers for separately mixing the received signal with the quadrature signals to provide a first and second output signal each in quadrature at the outputs of said mixers. These signals are low pass filtered. The demodulator includes third and fourth mixers with each mixer respectively receiving at an input one of the first and second low pass signals. At another input the mixers receive third and fourth signals. The third and fourth signals are derived from mixing a variable controlled oscillator (VCO) signal with local oscillator quadrature signals the frequency of said is independent of the center frequency of the received signal.

Abstract: A receiver for frequency modulated signals, having down-conversion to a baseband, zero intermediate frequency for selectivity, followed by up-conversion to a non-zero IF for amplification, limiting, and demodulation.A phase-lock loop locks the frequency of the down-conversion source to the center frequency of the signal coupled to the baseband IF, converting the signal to precisely zero frequency. This avoids the beat note often found in direct conversion systems. The phase-lock loop additionally provides inherent demodulation of the FM signal.The received FM signal is coupled to the baseband IF through a radio frequency amplifier for improved sensitivity and local oscillator isolation, or through a first IF comprising a mixer, local oscillator, filter, and amplifier.