1943-10-25

Abstract of GB556852 556,852. Frequency modulation. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. Oct. 1, 1942, No. 13799. Convention date, Oct. 2, 1941. [Class 40 (v)] A frequency modulator comprises two backcoupled valves operating with a common piezoelectric crystal and tank circuit, but with reactances of different sign in the respective feed-back circuits so that the valves tend to operate at different frequencies ; and the modulating voltage is applied differentially to control elements in the valves. As shown, the crystal X is connected between the anodes and the control grids of the valves V1, V2, the grid connection of one including a condenser C and of the other an inductance L. Resistances R1, R2 connect the respective grids to the earthed cathodes, and a common tank circuit Cl, L1 is connected between the anodes and HT+. Modulating voltage is applied through a transformer T in push-pull relation to the positive outer grids of the valves, so that the transmitted frequency varies continuously as each valve in turn predominates in its effect. The modulating voltage may be applied to the inner control grids, Fig. 3 (not shown). In a modification, the crystal X is connected between the cathodes and the junction of the condenser C and inductance L, which junction is connected to the anodes by a variable condenser, Fig. 2 (not shown).

0

1943-10-25

H03C3/16 ; H03C3/00

H03C3/16

GB19420013799 19421001

US19410413292 19411002

US2318979 (A1)

1	A improved frequency-modulated oscillation generator
	Inventor:	Applicant: MARCONI WIRELESS TELEGRAPH CO
	EC:H03C3/16	IPC: H03C3/16;H03C3/00
	Publication info: GB556852 A - 1943-10-25
2	Frequency modulator
	Inventor: USSELMAN GEORGE L	Applicant: RCA CORP
	EC:H03C3/16	IPC: H03C3/16;H03C3/00
	Publication info: US2318979 A - 1943-05-11

claim is:-

1 A frequency modulated oscillation generator including a pair of thermionic valves, a common tank circuit connected at one end to a like output electrode of each valve, a feed-back circuit between said tank circuit and a control electrode of each valve, and means for modulating differentially the impedances of said valves by the signal to be transmitted, wherein part of the úeed-back circuit is common to both valves and includes a piezo-electric crystal and parts are individual to each valve, the individual part for either valve including a reactance which is of different character from that included in the individual part for the other valve, the whole arrangement being such that each valve by itself with the common tank circuit and the common and its own individual parts of the feed-back circuit would tend to generate oscillations of a frequency different from that of the oscillations whic h would tend to be generated by The other valve by itself with the common t'ank circuit and the common and its own individual parts of the feed-back circuit, but' that because of the coupling provided by the common.

parts they together generate oscillations of a mean frequency being that of the crystal, and that this mean frequency is variable between the individual frequencies, as limits, as the said impedanoes are differentially modulated 60 2 A modulated generator as claimed in claim 1 in which the two valves have their anodes connected together and to this said one end of the tank circuit which i's in the common anode circuit 66 3 A modulated generator as claimed in claim 1 or 2, wherein said one end of said tank circuit is connected to the anode of each valve and through said crystal and a capacitor to the control electrode of 70 one valve and through said crystal and an inductor to the control electrode of the other valve.

4 A modulated generator as claimed in claim 1 or 2, wherein said one end of said 75 tank circuit is connected to the anode of each valve and through a first and second capacitor to the control electrode of one valve and through said first capacitor and an inductor to the control electrode of the 80 other valve, and 'through said first capacitor and said crystal to the cathodes of both valves.

A modulated generator as claimed in any of claims 1 to 4 in which each valve 85 has a resistance in parallel with its grid cathode circuit and the parallel combination'is in series in the feedback circuit with said -capacitor or said second capacitor in the case of one valve and with 90 said inductance in the case of the other valve.

6 A modulated generator as claimed in any of claims 1 to 5, in which each valve has at least two grids to one of 95 which said 'feedback circuit is connected and to the other the signal is applied.

7 A modulated generator as claimed in claim 5, w'herein the signal is differentially applied to the cathode end of sald 100 resistors which are applied to the cathodes by means of blocking capacitors.

8 A frequency mddriated generator substantially as described with reference to any one of the figures in the accom 105 panying drawings.

Dated this 1st day of October, 1942.

CAIRPMAELS & RANSFORD, Agents for Applicants, 24, Southampton Buildings, London, W G 2.

Leamington Spa: Printed for His Mfajesty's Stationery Office, by the Courier Press -1943.

PATENT SPECIFICATION

Convention Date (United States of America); Oct 2, 1941 556,852 Application Date (in United Kingdom): Oct 1, 1942.

Complete Specification Accepted: Oct 25, 1943.

No 13799/42.

(Under Section 6 (I) (a) of the, Patents,etc (Emergency) Act 1939, the proviso to Section 91 ( 4) of the Patents and Designs Acts; 1907 to 1942, became operative on April 19, 1943) COMPLETE SPECIFICATION -

A Improved Frequency-Modulated Oscillation Generator We, MARCONI'S WIRELESS Tr LEGR APHI COMPANY LIMITED, a company organised under the laws of Great Britain, of Marconi Offices, Electra House, Victoria Embankment, London, W C 2, assignees of GEORGE LINDLEY USSBLMAN, a citizen of the United States of America, of Port Jefferson, Long Island, New York, United States of America, do hereby declare the nature of this invention and in what manner the same is to be performed, to be partieularly described and ascertained in and by the following statement:

This invention relates to a new and improved modulated oscillation generator wherein substantially linear frequency modulation may be obtained The object of the present invention is to provide a simple and efficient frequency-modulated oscillation generator having a minimum number of valves and a minimum amount of circuit apparatus or circuit elements in the modulator circuits.

According to this invention, a frequency modulated oscillation generator includes a pair of thermionic valves, a common tank circuit connected at one end to a like output electrode of each valve, a feedback circuit between said tank circuit and a control electrode of each valve, and means for modulatingo differentially the impedances of said valves by the signal to be transmitted, wherein part of the feedback circuit is common to both valves and includes a piezo-electric crystal and parts are individual to each valve, the individual part for either valve including a reactance which is of different character fromn that included in the individual part of the other valve, the whole arrangement being such that each valve by itself with the common tank circuit and the common and its own individual parts of the feedback circuit would tend to generate oscillations of a frequency different from that of the oscillations which would tend to be generated by the other valve by itself with the- common tank circuit and the common and its own individual parts of the feedback circuit, but that because of the couplinigprovided by the common parts they together generate oscillations of a mean frequency, being that af the crystal, and lPrice 11-l that this mean frequency is variable between the individual frequencies, as 55 limits, as the said impedances are differentially modulated.

The invention is illustrated by the accompanying drawings, wherein each of the figures 1 2 and 3 shows a frequency ( 60 modulated oscillation generator comprising two valves with their electrodes regeneratively coupled in oscillation generating cireuits including a single crystal In the arrangement of figures 1 65 and 3, the crystal is connected between the anodes and grids of the valves so that feedback energy in both valves is by way of the crystal, whereas in figure 2 the crystal is eonnected in common between 70 the grids and cathodes of the valves an:t the feedback energy from the anodes to the grids is by way of a common condenser.

Referring to figure 1, valves V, and V 2 75 have their anodes 2 and 4 connected directly together and to a tank circuit Ll-01, to which an output circuit may be coupled by means of an inductance L 2.

The control grids 8:and 10 are connected 80 to the cathodes 12 and 14 of valves V, and V 2 by resistances R, and R 2 respectively.

The econtrol grid 8 of valve V, is connected to the anode 2 of valve V, by way of a variable phase shifting capacity 85 C and a crystal X The control grid 10 of valve V is connected to the anode 4 of valve V, by way of a phase shifting inductance L and the crystal X Modulation is applied differentially to the grids 90 16 and 18 from the secondary winding of a transformer T, the grids 16 and 18 being connected direct to earth as far as radit, frequency voltages are concerned by way of by-passing condensers BC 95 In figure 1 the anodes of valves V 1 and V, are connected to one end of the tuned tank circuit Cl-I Ll The other end of the tun ed tank circuit is earthed for radio frlquency voltages by means of 'R by-pass 100 eondenser BC Direct current for the anodes 2 and 4 is fed in at the earthed end of the tuned circuit The cathodes of the valves V 1 and V, are earthed A ste,,dy bias is applied to the screen grids 10,5 from a source S through a centre tap on 556,852 the secondary winding of transformer T, by which modulating voltages derived from source /l are applied to these screen grids.

Since one electrode of the crystal X is connected to the anode end of the tuned circuit C 1-L 1, and the other electrode of the crystal is connected to the control grids of valves V 1 and V 2 through phase shifting elements C and L respectively, the control grids of valves V, and V are effectively connected in parallel to the said lother of the electrodes of the crystal through the phase shifting elements C and L Grid bias for the control grids is obtained by the grid leak action of resistors R 1 and R 2, which, as pointed out hereinafter, serve also as phase shifting elements.

The condenser C, together with resistance R 1 and the valve resistance in parallel therewith, and the grid to cathode capacity of the valve, constitute the feedback excitation phase shifting network for valve V 1 Since this network is capacitative in character, it advances the phase of the voltage supplied by it from the anode to the grid by way of the crystal The inductance coil L, together with the resistance of the valve V 2 in parallel with resistance R 2 and the grid to cathode capacity of valve V 2, similarly constitute the phase shifting (retarding) network of valve V 2.

In the circuit of figure 1, it may be considered that there are two oscillation generators, one of which includes valve V 1, tank circuit L 1-C 11, crystal X, and condenser C, and the other of which ineludes valve V 2, tank LI-C 1 l crystal X, and inductance L Oscillation generation is insured in each of these oscillators considered individually due to effects somewhat similar to those obtained in oscillators of the Pierce type The feedback energy from the anode 2 and/or its tank circuit L 1-CI passes through the crystal to the control grid 8, thereby causing the crystal to oscillate in such a manner as to produce the proper phase relationship between the anode voltage and the excitation voltage reaching the control grid to maintain oscillation in the circuit The same remarks apply to the oscillation generator including 'valve V, crystal X, and inductance L However, as will be noted, the phase of the feedback voltage on the grid of valve V, is advanced, whereas the phase of the feedback voltage on the ( 30 grid of valve V 2 is retarded This causes the valves V, and V to tend to operate at different frequencies However, due to the locking-in effect produced by the close coupling between the two valves, they operate together to provide a single generated frequency, to which ihe circuit Li-Cl is tuned This is assuming conditions similar to those obtained with no modulation applied to the two valves In this case the valves operate at a mean ire 70 qtency between the frequencies at which the valves considered individually tend to oscillate This means frequency may be considered as the carrier frequency of the modulation system 75 When modulation voltages are applied to the valves differentially, the balance described above is upset, and one valve has an output larger than the other Due to the phase a(lvancing and retarding net 80 work, including CR, and L Ri, the phase of that valve supplying the greater amount of power to the tank circuit LI-C 1 will control, and the frequency of the output oscillations'will shift in one direction, z 5 i.e, towards the frequency at which that valve considered alone tends to operate.

When the grid voltages are modulated in the opposite sense by the modulating voltages, the resultant frequency is j 90 shifted in the opposite direction.

The arrangement of figure 2 is similar in many respects to that of figure 1, but it will be noted that the crystal X is connected between the control grids and 95 cathodes of the two valves and that the feedback voltages which provide the regenerative effect are supplied from the anodes 2 and 4 in common by way of a variable condenser C 2 This condenser C,, 100 as shown, is connected between the anodes and tuned tank circeuit C 1-L 1 and the junction point of the phase shifting reactances C and L The cathode end of the crystal X is eaithed This circuit is 105 soimewhall similar to the Miller crystal osceillator circuit Howev-er, in this case feedback excitation energy for the crystal X anl the control grids ofvalves V, aid V.2 is-obtained front the anode circuit 110 thirou Lgli the common condenser C.

The crystal oscillates in sueh a manner as to produce the correct phase relations in the excitation voltages-on the control grids to maintain oscillations in the cir 115 cults The phase of the excitation energy reaching the control grid of valve V, is advanced and the phase of the excitation energy reachino the control grid of valve V is retarded Thus as described above 120 the two valves considered as individual oscillators tend to operate at different frequencies When both valves deliver equal power, the circuit oscillates at the frequency of the crystal This assumes 125 that the tuned circuit Cl-L 1 has been tuned to operate at the frequency of the crystal When the power outputs of valves V, and V, are differentiall modulated by the signal oscillations, the carrier 130 F 556,852 energy will be frequency modulated in accordance with the signal oscillations as in the case of figure 1.

The system of-figure 3 is in general the same in circuit arrangement and operation as the system of figure 1 In figure 3, -however, modulation is applied differentially to the grids 8 and 10 by way of the biasing and phase shifting resistances R 1 I and R 2.

In all the arrangements described above amplitude modulation is balanced out.

In operation a frequency shift of -300 cycles was obtained at a carrier frequency of 2160 kc Due to the use of a single crystal in the two individual oscillator circuits, which cooperates to produce oscillations of a single frequency capable of being modulated, a simple, efficient frequency modulator using a small amount of apparatus is provided.

Having now particularly described and ascertained the nature of our said inven tion and in what manner the same is to be performed, we declare that what we