Compact, direct fm modulator providing constant deviation on each of a plurality of adjustable center frequencies

Claim 2

In a direct, frequency modulated oscillator having an electron device for sustaining oscillation and a frequency controlling circuit connected to said electron device for controlling the frequency of oscillation, the frequency controlling circuit being adapted to facilitate center frequency adjustment without causing a change in deviation and including in combination: a center frequency determining circuit comprised of a piezoelectric element and adjustable reactive means, said center frequency determining circuit having first and second terminals, said first terminal being connected to the electron control device, said piezoelectric element being resonant at a frequency determined by an equivalent reactance connected therewith, said adjustable reactive means being adjustable to change said equivalent reactance to thereby adjust the center frequency of oscillation; voltage variable capacitor means coupled to said second terminal of said center frequency determining circuit and forming part of said equivalent reactance; means applying a modulating voltage to said voltage variable capacitor means to change the capacitance thereof thus varying said equivalent reactance to deviate the frequency of oscillation, said piezoelectric element having a tendency to change the deviation as said adjustable reactive means is adjusted, the values of the components of the frequency controlling circuit being selectively chosen such that a change in said variation of said equivalent reactance provided by said voltage variable capacitor means is produced by said adjustment of said adjustable reactive means, said change in the variation of said equivalent reactance compensating for said tendency of the piezoelectric element to change the deviation.

Claim 3

The combination of claim 1 wherein said piezoelectric element is a quartz crystal constructed to have a low inductance on the order of 7 microhenries at the center frequency of oscillation and wherein the difference between the series resonant frequency of said quartz crystal and the antiresonant frequency thereof is on the order of 440 parts per million.

Claim 4

The combination of claim 1 wherein said frequency controlling circuit includes a plurality of said center frequency determining circuits each having first and second terminals, first circuit means coupling said second terminal of one of said center frequency determining circuits to said voltage variable capacitor means; and second circuit means selectively connecting one of said first terminals to the electron device for determining different center frequencies of oscillation, any of said center frequency determining circuits being adjusted by adjusting said corresponding adjustable reactive means without changing the frequency deviation caused by a modulating voltage having a constant amplitude.

Claim 5

The combination of claim 1 wherein said adjustable reactive means includes an adjustable inductor which is connected in series with said piezoelectric element.

Claim 6

A frequency modulated crystal controlled oscillator, including in combination: an electrOn device; a first center frequency determining circuit having a first piezoelectric crystal, a second center frequency determining circuit comprised of the series connection of a second piezoelectric crystal and an associated variable reactance means, each of said crystals being responsive to the equivalent reactance connected therewith to individually determine a center frequency of oscillation, voltage variable capacitor means connected to at least one of said center frequency determining elements, means coupling a modulating signal to said voltage variable capacitor means to change the capacitance thereof thus varying said equivalent reactance to deviate the frequency of oscillation, switching means selectively connecting one of said first and second frequency determining circuits between said electron device and said voltage variable capacitor means, said second crystal when connected to said electron control device having a tendency to increase the deviation as the reactance of said associated variable reactance means is decreased and a tendency to decrease the deviation as the reactance of said variable reactance means is increased, the values of the components of the oscillator being selectively chosen such that said change in the capacitance of the voltage variable capacitor provides a decreased change in said equivalent reactance as said reactance of said variable reactance means is decreased and an increased change in said equivalent reactance as said reactance of said variable reactance means is increased to compensate for said tendency of said second crystal to change the deviation.

Claim 7

A frequency modulated crystal controlled oscillator, including in combination: an electrOn device; a first center frequency determining circuit having a first piezoelectric crystal, a second center frequency determining circuit comprised of the series connection of a second piezoelectric crystal and an associated variable reactance means, each of said crystals being responsive to the equivalent reactance connected therewith to individually determine a center frequency of oscillation, voltage variable capacitor means connected to at least one of said center frequency determining elements, means coupling a modulating signal to said voltage variable capacitor means to change the capacitance thereof thus varying said equivalent reactance to deviate the frequency of oscillation, switching means selectively connecting one of said first and second frequency determining circuits between said electron device and said voltage variable capacitor means, said second crystal when connected to said electron control device having a tendency to increase the deviation as the reactance of said associated variable reactance means is decreased and a tendency to decrease the deviation as the reactance of said variable reactance means is increased, the values of the components of the oscillator being selectively chosen such that said change in the capacitance of the voltage variable capacitor provides a decreased change in said equivalent reactance as said reactance of said variable reactance means is decreased and an increased change in said equivalent reactance as said reactance of said variable reactance means is increased to compensate for said tendency of said second crystal to change the deviation.

Claim 8

The oscillator of claim 5 wherein each of said piezoelectric crystals is a quartz crystal constructed to have a low inductance on the order of 7 microhenries at the center frequency of oscillation and wherein the difference between the series resonant frequency of said quartz crystal and the antiresonant frequency thereof is on the order of 440 parts per million.

Claim 9

The oscillator of claim 5 wherein a circuit branch including a series connected capacitor and inductor is connected in parallel with said voltage variable capacitor; said modulating voltage is applied to the junction between said series connected inductor and capacitor, and the values of said capacitor and inductor are selectively chosen so that the frequency deviation varies linearly with the amplitude of said modulating voltage.

Claim 10

The oscillator of claim 5 wherein said variable reactance means includes a variable inductor.

Claim 11

The oscillator of claim 5 wherein said electron device is a transistor.

Claim 12

In a frequency modulated oscillator comprised of an amplifier having an electron device and a frequency controlling feedback network, said feedback network including in combination, voltage variable capacitor means, a first piezoelectric crystal having first and second terminals, said first terminal being connected to said voltage variable capacitor means, first circuit means comprised of a series connected first variable inductor and capacitor, said first circuit means being connected across said voltage variable capacitor, source of modulating voltage coupled to the point between said first variable inductor and capacitor of said first circuit means, second circuit means having first and second terminals and comprised of a second piezoelectric crystal connected in series with a second variable inductor, said first terminal of said second circuit means being coupled to the first terminal of said first piezoelectric crystal, switching means having a plurality of input terminals and a sole output terminal, said switching means being operable to connect any one of said plurality of input terminals to said output terminal, said output terminal of the switching means being connected to the electron device, said second terminal of the first piezoelectric means being connected to one of said plurality of said input terminals of the switching means, said second terminal of said second circuit means being coNnected to another of said input terminals of the switching means, said switching means being operable to connect either said second circuit means or said first piezoelectric means to said electron device to thereby select either of two center frequencies of oscillation, said selected frequency of oscillation being deviated in response to changes in the capacitance of said voltage variable capacitor means in response to a modulating voltage, adjustment of said second variable inductor tending to change the deviation when said second circuit means is connected to said electron device, said components of the oscillator being selected so that the effect of said change in capacitance of said voltage controlled capacitor is changed as said second variable inductor is adjusted to counterbalance said tendency of said deviation to change with said adjustment.

Claim 13

In a frequency modulated oscillator comprised of an amplifier having an electron device and a frequency controlling feedback network, said feedback network including in combination, voltage variable capacitor means, a first piezoelectric crystal having first and second terminals, said first terminal being connected to said voltage variable capacitor means, first circuit means comprised of a series connected first variable inductor and capacitor, said first circuit means being connected across said voltage variable capacitor, source of modulating voltage coupled to the point between said first variable inductor and capacitor of said first circuit means, second circuit means having first and second terminals and comprised of a second piezoelectric crystal connected in series with a second variable inductor, said first terminal of said second circuit means being coupled to the first terminal of said first piezoelectric crystal, switching means having a plurality of input terminals and a sole output terminal, said switching means being operable to connect any one of said plurality of input terminals to said output terminal, said output terminal of the switching means being connected to the electron device, said second terminal of the first piezoelectric means being connected to one of said plurality of said input terminals of the switching means, said second terminal of said second circuit means being coNnected to another of said input terminals of the switching means, said switching means being operable to connect either said second circuit means or said first piezoelectric means to said electron device to thereby select either of two center frequencies of oscillation, said selected frequency of oscillation being deviated in response to changes in the capacitance of said voltage variable capacitor means in response to a modulating voltage, adjustment of said second variable inductor tending to change the deviation when said second circuit means is connected to said electron device, said components of the oscillator being selected so that the effect of said change in capacitance of said voltage controlled capacitor is changed as said second variable inductor is adjusted to counterbalance said tendency of said deviation to change with said adjustment.

Claim 14

The combination of claim 10 further including a plurality of said second circuit means, said first terminals of said plurality of circuit means all being coupled to said voltage variable capacitor means, each of said second terminals of said plurality of the second circuit means being connected to separate ones of said plurality of input terminals of said switching means.