Abstract: An optical injection locking oscillator is comtemplated having a tuning device. The tuning device generates a DC voltage proportional to the resonant frequency of a modulated light used to injection lock the free running oscillator. The DC voltage is applied to a varactor capacitor within the oscillator to bring the frequency of oscillation within a close proximity to the modulating frequency of the light. This facilitates injection locking, whereas frequencies of oscillation outside a certain locking range will not facilitate injection locking. The modulated light then locks the oscillator into a desired resonant frequency. A second embodiment contemplates using a YIG oscillator regulated by a DC current generated within the tuning device.

Abstract: A negative-resistance diode oscillator tuned by a varactor as applicable to frequency-modulated transmitters or to receiver oscillators operating within the 56-100 GHz frequency band is integrated in a waveguide. The diode is encapsulated in a capped package and mounted on a ground-connected base. A coupling capacitor is fixed on the metallic cap of the package. A varactor having beam-lead connections is mounted as a bridge between the capacitor and a ground-connected metallic stud. The bias voltages are brought in the plane of the waveguide by means of two wires and two capacitors housed within orifices formed through the waveguide walls.

Abstract: In an electronic tuning circuit for AM receiver including a radio-frequency tuning circuit and local oscillator circuit each using a variable capacitance diode, the local oscillator circuit comprises an oscillation coil; a padding capacitor connected in series with the oscillation coil; a first variable capacitance diode connected at one end in series with the oscillation coil; a first and a second fixed capacitor connected at one end in series with each other; and a second variable capacitance diode connected in parallel with the second fixed capacitor. The second fixed capacitor has its other end connected to a connection point between the padding capacitor and the first variable capacitance diode. The first fixed capacitor has its other end connected to the connection point between the oscillation coil and one end of the first variable capacitance diode. A tuning voltage is applied to the first and second variable capacitance diodes, thereby reducing tracking error over the entire receiving frequency band.

Abstract: Disclosed is a local oscillator using a dielectric coaxial resonator (27), which is availably used as a fixed local oscillator in double-spot tuners and CATV converters, and which is arranged so that an AFC voltage is applied to a variable-capacitance diode (23) from an output terminal (E) of a frequency control circuit through a first resistor (35), the variable-capacitance diode having its one end being connected to a center conductor of a dielectric coaxial resonator (27) through a capacitor (25) and its other end being AC grounded, and that a first reference potential (V.sub.A) lower than a source voltage (V.sub.CC) by a predetermined value is given to the variable-capacitance diode (23), the one end of the variable-capacitance diode (23) being connected to the source voltage (V.sub.

Abstract: A temperature-compensated piezoelectric oscillator of high-spectral purity, capable of being controlled in frequency, consists of a compensation circuit, a processing circuit, a phase-shifting circuit, containing the piezoelectric resonator, and an oscillating circuit. To obtain high spectral purity, it is proposed to use a low-pass filter, placed between the compensation circuit and one of the inputs of the processing circuits, to process the signal coming from the compensation circuit. This filter eliminates the influence of the temperature noise coming from the compensation circuit. The invention can be applied to controllable frequency, temperature compensated piezoelectric oscillators where high spectral purity is sought.

Abstract: A fully integrated, adjustable oscillator circuit for use with a crystal is disclosed in which a crystal oscillator, such as a Pierce oscillator, is arranged to utilize a tuning network that includes at least one integrated varactor (voltage-variable-capacitor) as a shunt element for providing at least one type of adjustment of the oscillating signal. More than one type of adjustment can be provided by including a bank of varactors for each of the shunt elements of the tuning network, in which various individual varactors are selected in binary (on-off) fashion to effect digital as well as analog adjustment of the crystal oscillator.

Abstract: A variable capacitive semiconductor element is connected to a piezo-electric resonator for controlling the oscillating frequency thereof according to the variable capacitance of the capacitive element. The variable capacitive semiconductor element comprises a floating electrode disposed on and electrically isolated from a semiconductor substrate for storing electric charge to form a capacitance region in the semiconductor substrate, a control electrode for injecting electric charge into the floating electrode to determine the amount of capacitance, and a terminal electrode for connecting the variable capacitive element to the piezo-electric resistor. A bias circuit is connected to apply a given voltage to the terminal electrode to adjust the amount of capacitance according to the given voltage.

Abstract: A voltage-controlled oscillator includes a negative resistance generator, a resonant circuit, a first series circuit, a second series circuit, and a third series circuit. The first series circuit controls an oscillation frequency for changing a resonant frequency of the resonant circuit, and the second series circuit modulates this frequency. The third series circuit consists of a capacitor and a variable capacitance diode to which the modulation signal is supplied. The third series circuit changes the resonant frequency of the resonant circuit in a direction for cancelling a change in modulation sensitivity caused by the second series circuit.

Abstract: The local oscillation circuit in accordance with the present invention is characterized as follows. The collector of an oscillation transistor is grounded for atlernating current. A series resonance circuit consisting of a variable capacitance diode and a resonator is connected to the base of the oscillation transistor. The other end of the series resonance circuit is grounded for alternating current. The emitter of the oscillation transistor is connected to the collector of an amplifying transistor. The emitter is grounded through a capacitor that removes or reduces the a.c. component and passes the d.c. component. An oscillation signal taken from the emitter of the oscillation transistor is fed to the base of the amplifier transistor. A local oscillation output signal is taken from the collector of the amplifier transistor, and bias potential to the amplifier transistor is impressed from the power source to the base of the amplifier transistor.

Abstract: A receiver equipped with an electronic tuning circuit which uses voltage-variable reactance elements such as variable-capacitance diodes or the like in the radio-frequency tuning circuit and oscillation tuning circuit thereof. The oscillation tuning circuit includes a novel padding capacitor constituted by a composite circuit of a variable-capacitance diode and fixed capacitors connected at the position where a conventional padding capacitor is connected. With such an arrangement, it is possible to make tracking error negligibly small over a frequency band ranging from a low receiving frequency to a high receiving frequency, by applying a tuning voltage to the composite padding capacitor.

Abstract: A crystal oscillator in a bridge circuit coupled to a differential amplifier. Coordinated adjustment of one or two arms of the bridge permits pulling of the crystal's operating frequency both above and below its series resonant frequency.

Abstract: This microwave oscillator in one embodiment has two tuning rods (16 and 18) configured to extend within a resonant cavity (12). One of these tuning rods (18) attaches to a shaft (19) that is affixed at one end and that is comprised of a material having a thermal coefficient of expansion that is different from the material comprising the housing (11) that forms the cavity (12). As a result, movement of the tuning rods (16 and 18) will vary as temperature varies, with a resulting stability in the frequency of oscillation.

Abstract: A voltage controlled oscillator circuit of a type having a tank circuit for generating oscillations which includes a means for establishing a fixed bias voltage with respect to ground at a bias end of said tank circuit, means for drawing current from an a.c. end of said tank so as to control the tank gain, and an AGC capacitor. A constant current source is coupled to the AGC capacitor for supplying it with a constant charging current. Means are provided for discharging the AGC capacitor at a voltage level determined by a ratio of resistors and a transistor emitter-base ratio.

Abstract: A frequency-doubling voltage-controlled oscillator (VCO) for use in the microwave frequency range has two channels which operate in parallel. A transistor is mounted as an oscillating system in each channel and its energy is collected on the drain electrode. The two transistors are mounted with their output currents in opposite phase, thus reducing FM noise in the vicinity of the carrier. In accordance with the invention, phase opposition is obtained by means of a varactor connected between the gates of the two transistors. The varactor is decoupled in direct current by means of two capacitors. In order to increase the range of frequencies, two additional varactors can be mounted in like manner on the source circuits of the two transistors.

Abstract: The present invention relates to a local oscillation apparatus which is used as a local oscillator of a communication apparatus or as a fixed local oscillator of a tuner. The present invention comprises a coaxial resonator (1) and an amplifying circuit (26) having an output end connected to a central conductive member of the coaxial resonator (1) through a first capacitor (2), an input end connected to the central conductive member through a second capacitor (3), and a variable capacitance diode (5) having one end connected to the central conductive member of the coaxial resonator (1) through a third capacitor (4) and the other end grounded so as to permit an alternating current only to be flowed.

Abstract: A modulation and range shift device for use with a PLL frequency synthesizer VCO. The modulation signal is provided to the negative side of the tuning varactor (16) of the VCO (14). In addition, variable voltages can be applied to the negative side of the tuning varactor (16) to achieve range shift as desired. Component variations in the modulation section (18) need not be varied to accommodate changes in the loop filter (12 and 13) of the PLL circuit.

Abstract: The resonant frequency of a quartz-crystal microwave oscillator is the fundamental frequency in the partial mode of the crystal and makes it possible to maintain the loaded Q of the resonator at a high value. This microwave oscillator is provided with two amplifying stages and has a signal-to-noise ratio of the order of 160 dB.

Abstract: A local oscillator is arranged in a Colpitts type configuration in which an amplifying device such as a bipolar transistor or field effect transistor having a control electrode (base or gate electrode) is coupled to a first electrode (emitter or source electrode) defining the end of a conduction channel through an oscillation conditioning network conditioning the device to oscillate in a given range and also to a frequency determining network including a first varactor diode responsive to the tuning voltage and an inductance element coupled in series between the control electrode and signal ground, and in which the output is taken at a second electrode (collector or drain) defining the other end of the conduction channel. A range extending circuit including a second varactor diode responsive to the tuning voltage is coupled between the control electrode and signal ground for ensuring that the oscillator operates reliably at both ends of the tuning range.

Abstract: An integrated voltage controllable oscillator having a transistor for oscillation is further provided with a resonance circuit externally connected to two electrodes of the transistor for oscillation and including a variable capacitance element adapted to vary a resonance frequency of the resonance circuit, and a high impedance element connected between the variable capacitance element and the ground in a circuit adapted to supply a control voltage to the variable capacitance element.

Abstract: A four-diode bridge is positioned within the cavity of a Gunn diode oscillator. A subharmonic signal is applied to the diode bridge and the diode bridge couples an odd harmonic of the injected signal into the cavity. The cavity is thus caused to resonate at the odd harmonic of the injected signal. The injected signal can be changed using a frequency synthesizer in order to provide a microwave oscillator with multiple-channel operation. The diode bridge provides a feedback signal indicative of the phase of cavity oscillation. The feedback signal is applied to a varactor which pretunes the Gunn diode oscillator and thereby provides phase-locked control.

Abstract: An improved oscillator circuit utilizing multiple semiconductor devices, such as field-effect transistors or bipolar transistors, is disclosed. To improve the gain of the oscillator circuit corresponding terminals on each device are interconnected via a path which provides a delay equal to an integer multiple of the inverse of the oscillator frequency. This technique can be adapted to provide an oscillator whose nominal frequency is voltage controllable and can be arranged to provide one or more output ports.

Abstract: Frequency/temperature compensation of millimeter wave lumped active element oscillators is disclosed by use of a simple capacitive compensating element, and including printed circuit versions in which the temperature compensating capacitor is printed in-situ with the circuit elements.

Abstract: A high-frequency modulator which is linearly modulated in a frequency range around a center frequency and comprises a high-gain field effect transistor whose output is fed-back to the input from a coupler constituted by two relatively fine lines which are sufficiently remote from each other to provide that at the input of the transistor the majority of the high power available at its output is reinjected, and thus a high external Q factor is obtained. The modulation circuit which is arranged in parallel with the feedback network includes a varicap which is arranged in series with three line elements and a fixed capacitor calculated for optimizing the linearity of the frequency modulation as a function of the control voltage of the varicap. The circuit may be used for example, in equipment such as radio altimeter sources or proximity fuses, auto-directional systems and long-range radar.

Abstract: A voltage-controlled-oscillator with a modulator, comprising a first variable capacitance diode, a second variable capacitance diode, and a third variable capacitance diode. The second variable capacitance diode is connected in series with the third variable capacitance diode to form a serial connection member.

Abstract: A voltage-controlled-oscillator with a modulator, comprising a first variable capacitance diode and a second variable capacitance diode. The first variable capacitance diode is connected in series with the second variable capacitance diode to form a resonance device, wherein capacitance of the first variable capacitance diode is controlled by applying a reverse bias voltage and an oscillation frequency control voltage to both ends of the first variable capacitance diode, and capacitance of the second variable capacitance diode is controlled in a reverse direction to changes in the capacitance of the first variable capacitance diode with respect to the oscillation frequency control voltage by applying the oscillation frequency control voltage and a modulation signal to both ends of the second variable capacitance diode to thereby provide a frequency modulated wave.

Abstract: A variable capacitance circuit includes a varactor having an anode side and a cathode side. A first variable bias voltage is applied to one of the sides and one of a plurality of voltages is applied as a second bias voltage to the other side for controlling the capacitance of the varactor. A voltage multiplier circuit connected to a voltage divider network is used for supplying the plurality of voltages. A decoder is responsive to input signals for selecting and applying one of the multiple voltage outputs. The variable capacitance circuit is used in a voltage controlled oscillator of a frequency synthesizer for providing extended frequency range.

Abstract: A TVRO receiver utilizes an improved voltage-controlled oscillator (VCO) of the surface mounted type which has a wide bandwidth of operation extending into the microwave frequency range. The VCO comprises a dielectric substrate with a patterned-metal layer on one side and a surface mounted oscillator on the patterned-metal side of the substrate. The oscillator comprises amplifying means which produce an oscillating output by the use of regenerative feedback means including an open-circuit-stub inductance formed in the patterned metal layer, and a tunable resonant circuit coupled to the amplifying means in order to control the frequency of the oscillating output. The resonant circuit includes a short-circuit-stub capacitance formed within the patterned middle layer, at least one variable capacitance diode in series with the short-circuit stub, and means for applying a controllable tuning potential to the resonant circuit.

Abstract: A dual gate field effect transistor (FET) is configured as a self-buffering local oscillator of a tuner by arranging the FET in a cascode configuration in which the first gate electrode is coupled to the source electrode through an oscillation conditioning network and also to a frequency determining network, the second gate electrode is coupled to signal ground through a negligible impedance and the drain electrode is utilized as the output of the oscillator.

Abstract: A microwave frequency oscillator capable of being linearly swept over a wide frequency range around a central frequency comprising a field-effect transistor with a high gain, the output of which is fed back to the input from a coupler consisting of two relatively narrow striplines located close together. A wobbulator circuit is fitted in shunt to the feedback network comprises two voltage variable capacitors in series between three line components designed to optimize the frequency modulation linearity in relation to the voltage variable capacitance diode control voltage. The oscillator is useful in equipment requiring extreme linearity such as radio-altimeter sources.

Abstract: A low noise two port voltage controlled oscillator having a coarse tuning circuit serially connected to an inductor to form a resonant circuit. A fine tuning circuit is serially connected between the resonant circuit and the input to the amplifier. A large capacitance series silicon varactor minimizes noise at the frequency of operation while optimizing the coarse tuning range.

Abstract: Tuning varactor circuitry is disclosed for a dielectric resonator stabilized oscillator (2). A varactor diode (22) is electrically connected in a loop (24) with an RF bypass capacitor (26), and the voltage across the diode is varied. In a first embodiment, first and second dielectric substrates (36, 38) face each other along the plane of the loop (24), with the loop (24) therebetween. In another embodiment, the loop (24) is around a peripheral side wall (52) of the dielectric resonator substrate (46). In another embodiment, the loop (24) is formed on the same surface (54) of a microstrip circuit substrate (56) with a transmission line (10).

Abstract: A UHF oscillator circuit includes a plurality of first leadless, or "chip", surface mounted components machine positioned on a first side of a printed circuit (PC) board and a plurality of second lead-bearing components mounted on a second side of the PC board and coupled in circuit through the PC board to the chip components in an arrangement which substantially reduces circuit fabrication costs. Comprised of a majority of automatically positioned surface mounted chip components and making use of a minimum number of lead mounted discrete components, the low Q values of the surface mounted components are compensated for by an external surface mounted feedback capacitor coupled across the collector-emitter junction of a common base transistor to provide oscillator tuning over a frequency range greater than an octave.

Abstract: A broadband high frequency power oscillator employing a GaAs FET transistor and a two-port coupling network whose input port is connected across the drain and source terminals of the GaAs FET. The coupling network consists of 3 branches in T- or .pi.-configuration. One branch includes a matching network and the load. The other two branches are purely reactive and each includes at least one independently tunable reactance element, such as a varactor.

Abstract: A voltage controlled oscillator includes automatic adjust circuitry to achieve and maintain desired operating characteristics such that for a predetermined output frequency the oscillator will have a predetermined input voltage. The oscillator may advantageously be incorporated into a phase locked loop circuit. The phase locked loop will lock onto the frequency of an input signal. Automatic adjust circuitry monitors the input to the voltage controlled oscillator in the phase locked loop and varies the amount of a bias voltage applied to the oscillator so that the input voltage to the oscillator will change until it reaches the desired level. The provision of the automatic adjust circuitry enables the desired operating characteristics of the oscillator to be maintained in spite of long term changes in the circuit operation.

Abstract: A high frequency oscillator having an oscillation transistor connected to a resonant strip line unit consisting of a main strip line member and an auxiliary strip line member. The auxiliary strip line member is connected in parallel with or isolated from the main strip line member by a switch diode for switching the characteristic impedance of the strip line unit so as to generate a reception or transmission carrier wave output. A varactor diode connected to the strip line unit has its capacitance changed through an applied control voltage for channel switching. A modulating signal input terminal is directly connected to a portion of the auxiliary strip line member for modulating an FM transmission signal independently of the value of the control voltage applied to the varactor diode.

Abstract: The invention concerns a very high frequency quartz oscillator. The feedback loop of the oscillator comprises a compensation network of a quartz at the frequency of the oscillator, and a low-pass filter eliminating the frequencies lower than that of the oscillator. A power divider having two branches allows to send the signal issuing from the feedback loop, on the one hand, to the amplifier input of the oscillator and, on the other hand, to the output amplifier. Two-port networks Q.sub.1 to Q.sub.6 match the impedances at the input and at the output of the amplifier of the oscillator, of the feedback loop and of the output amplifier.

Abstract: A microwave varactor network wherein parametric oscillation modes are suppressed by coupling the varactor, with very low intervening impedence, to a bias regulator circuit (preferably an emitter follower circuit) through which the varactor bias voltage is supplied. The emitter follower is biased to always be carrying current, which improves its response time in compensating any transient bias voltage variations which appear across the varactor.

Abstract: A voltage controlled oscillator of the type wherein a variable capacitance diode is connected in parallel with a distributed parameter line functioning as a resonance circuit, whose capacitance varies in response to voltage control. To vary the resonance wavelength of the distributed parameter line a condenser is connected in series therewith, and the condenser is short-circuited by a switching diode. A coaxial dielectric line, strip line, coaxial cable, etc. may be used as the resonance circuit element by dividing the distributed parameter line into two parts and employing these elements as the divided parts.

Abstract: A system and method for continuous tuning of a YIG oscillator over its entire operating range by control of a resolver in a feedback loop around the oscillator. The resolver and a delay line form a phase shift network the output of which is compared in phase with the output of the oscillator, which is also coupled to the input of the resolver, and the phase-difference signal resulting from the phase comparison is coupled to an integrator connected in turn to the tuning signal input of the oscillator. Repetitive operation of the resolver over its operating range enables continuous tuning of the oscillator over its entire operating range.

Abstract: An FM transmitter especially for physiological signal telemetry includes a transistor oscillator having a collector-to-base capacitance that is part of its tuned circuit. Means are disclosed for controllably varying the collector-to-base capacitance only in response to impressed physiological or other signals to provide FM modulated signals for aerial transmission to any suitable receiver. Means including cooperative constant emitter current and constant collector voltage DC biasing circuits are disclosed for eliminating undesirable, changing temperature induced frequency variations. Means are further disclosed for neutralizing undesirable antenna loading induced frequency variations. The system is capable of accepting multiplexed inputs.

Abstract: A frequency stable RF oscillator 10 comprises a variable frequency RF source in the form of a microwave cavity 24 having a Gunn diode 26 and a varactor 28 mounted therein, and produces an RF output frequency f.sub.o. The output of a frequency stable reference oscillator 14 having a frequency f.sub.r is impressed upon the RF source. Through self-mixing action of the Gunn diode, an IF whose frequency is f.sub.IF =.vertline.nf.sub.r -f.sub.o .vertline. is generated, n being a high harmonic number. The IF is detected by an IF amplifier 18 which forms part of a frequency lock loop controlling the frequency of the RF source.

Abstract: An injection locked RF oscillator comprises a variable frequency RF source 12 having a Gunn diode 20 and a varactor 22, and a frequency stable reference oscillator 14 whose output f.sub.i is injected into the source to cause injection locking of the source. The output of a low frequency perturbation oscillator 30 is applied to the varactor and the resultant variation in the current consumption I.sub.o of the Gunn diode detected by amplifier 28 and filter 36 to provide a control signal which is effective to shift the resonant frequency f.sub.o of the source 12 towards the frequency f.sub.i of the reference oscillator, or a harmonic thereof. A sweep-and-lock circuit 44 is provided to acquire injection locking upon switch-on.

Abstract: A direct frequency modulation crystal-controlled oscillator circuit is provided having a configuration which minimizes the number of parts required for modulation while maintaining a linear relationship between the incoming modulation voltage and the outputted frequency. The circuit includes a tuning diode in a parallel arrangement with a tank circuit connected to the collector of a transistor. In the preferred embodiment, the tank circuit includes only an inductor. The crystal of the circuit operates in the anti-resonant mode and its impedance is much greater than that of the tank circuit. Direct frequency modulation results from the frequency change of the crystal in responding to a phase change caused by the modulation voltage applied to the tuning diode, which subsequently results in a change in the phase of a transistor collector voltage.

Abstract: A tuning arrangement including a mixer stage, a tunable RF-circuit coupled to an input of said mixer stage, an oscillator circuit, coupled to another input of said mixer stage, having a tunable resonant circuit and, for both circuits, a common tuning to mutually different resonant frequencies, of which at least the circuit having the higher resonant frequency includes, a parallel circuit of, on the one hand, a circuit inductance and, on the other hand, a series arrangement of a tuning capacitor and a padding capacitor. For an acceptable tracking between the resonant frequencies of the two circuits, more specifically in the lower frequency portion of the tuning range, the padding capacitor is shunted by a coil which considerably reduces the effect of the capacitance of the padding capacitor at least in the lower frequency portion of the tuning range.

Abstract: A television signal generator for producing a composite RF signal without high level intermodulation products. A signal network is provided to linearly combine a first video modulated carrier signal and a second carrier frequency of the same frequency modulated with an audio modulated subcarrier. An audio subcarrier generator is disclosed having a ceramic resonator for a frequency determining circuit element. The resonator is parallel connected with a voltage sensitive reactance element to provide a frequency modulated subcarrier in response to a modulating voltage.

Abstract: A solid state oscillator circuit for operation at very high frequencies includes a field effect transistor having an input network connected between its gate and source electrodes and an output network connected between its drain and source electrodes, the input and output networks each including three discrete capacitors connected in a "pi" configuration, the input and output networks being connected in series with one another, and an inductor being connected in parallel with the series connected networks, the equivalent circuit impedance of the networks in series and the inductance determining the operating frequency of the oscillator circuit, and the relative ratio of impedance of the networks determining the amount of oscillator feedback.

Abstract: An FM demodulator having a phase comparator, a low-pass filter and a VCO including a variable capacitance diode, an input signal being applied to the phase comparator and a demodulated output signal being taken from the low-pass filter. The FM demodulator further includes a compensating circuit consisting of a non-linear element connected between the demodulated output terminal and the VCO, whereby the secondary distortion in the output signal to be caused due to the non-linearity of the variable capacitance diode is canceled.

Abstract: A voltage controlled oscillator is disclosed wherein a peak detector is used to control the gain of the active device within the oscillator in response to a control signal taken from the resonant circuit. The control signal is a RF potential developed across a voltage divider within the resonant circuit. By controlling the gain of the active device from an RF voltage provided by a voltage divider, the RF output level of the oscillator "tracks" the DC bias level of the steering line. Therefore, varactor diodes rectification is prevented while contemporaniously allowing maximized output power.

Abstract: A crystal oscillator circuit that is temperature compensated over a broad temperature range has a crystal oscillator, a reactance compensation circuit for providing temperature compensation at low temperatures, and a control voltage-generating circuit for providing temperature compensation at high temperatures. The reactance compensation circuit includes the parallel combination of a thermistor and a variable-capacitance diode, and this parallel combination is connected in series with the crystal oscillator. The control voltage-generating circuit includes a thermistor and transistors and applies a voltage corresponding to the ambient temperature to the variable-capacitance diode of the reactance compensation circuit.

Abstract: A method and apparatus for generating a sweep signal, the frequency of which is accurately known at all times during the sweep cycle. The beginning and ending frequencies are fixed by a phase-locked loop and the resulting error correction voltages are stored. During the sweep, these error voltages determine the offset and slope of the D.C. voltage ramp signal which governs the frequency of the sweep oscillator.