US2370720A - Magnetic frequency converter - Google Patents

Description

March 6, 1945.

H. DONLEY 2,370,720

MAGNETIC FREQUENCY CONVERTER Filed April 14, 1942 2 Sheets-Sheet l TIE] -1.

U a Q YS/GNAL 2N0. f/Amworwc S/QNA 1.

2N0. HARMON/C 0F OSCILLATOR OSc/LLATQR INVENTOR. Hugh 1. DONLEY.

ATTORNEY March 6, 1945. H. DONLEY v MAGNETIC-FREQUENCY CONVERTER .2 Sheets-Sheet 2 Filed April .4, 1942 INVENTOR. I 16 00. A. Down:

ATTbRA/EY s Q. be w @Q Q J .Patented Mar. 6, 1945 Hugh- L Danie! Golfingswondn N l; assignor' to Radio Corporation. of Ainericzn. a corporation of Delaware;

Application s irit :4, 1942, No..438;875;

I a'ci ims. (oceanic) The present invention: relates to amethod of and. a circuit arrangement for obtaining frequency conversionbymagnetic-means. v

In radio receivers of theheterodyne' or super stantially the, same efficiency. It is therefore. air

object of the invention to provide an alternative method and means of frequency conversion.

Since according to the invention the frequency conversion by" magnetic means is accomplished without the use of a vacuum} tube-as the detecting means, the elimination of tube noises-"and consequent increased signal to" noiseratio over the conventional vacuum tube heterodyne' converter are of decided advantage-at highand ultra-high frequencies. Other objects are toimprove generally the simplicity and efliciency of receivers of the,- heterodyne or superheterodyne types and to more particularly provide areceiveuwhi'chis not only reliable in operation but capable of economical manufacture and assembly: The novel features characteristic of, my invention are set'forth with particularityin' the appended claims. The invention itself, however; both as' tc' its construction andmode of" opera ti'ontogether-withfurther objects and advan tages thereof, will best be understood by refer ence to the following description, taken in con-: nection with the accompanying drawings. 1 in which Fi'g. 1- shows certain. curves inorder to explain the invention, Fig. 2 discloses a circuit arrangement embodying theinvention andwhich will serve-to demonstrate the conversion efficiency of this type of frequency mixer or converter, and Fig. 3 is a practical embodiment of the-invention nasuperheterody e receiver.

linear relationship exists between induction and magnetizing 'forceof ferro-magnetic cores. By reason thereof the magnetic effects may be used for the purpose of shifting the frequency band of a signal to a new band of frequencies. How ever, in order" to minimizeradio frequency losses a powdered magnetic material with agsuitable binder is utilized, an easily saturated materia like magnetitebeing the most efficient.

Referring to Fig. 1 the non-linear relation'be tween. induction: and. magnetizing current of'a ferro-magnetic core'that may be used tocarry The invention is based on thefact that a nonout'thcinvention is: shown by the curve Cu Illus= trated also are the oscillator current; wave; its: second harmonioandi the signal current wave.

The si'gnal fre quenoywhen addecl'to thecscillator secondharmonic.givesthecurveac. Hence, when thawave of such a form as illustrated: by c is impressed. upon the: characteristic. shown by a,

theresuitant waveb withitsobvious dissymmetry shows that detection has resulted. 1

The-frequency terms: present-tin almagnetic. de-

. teeter or converter; as an approximation, may

also be determined byconsiclering onlythe voltage: drop across: the coil. containing: the saturable This. voltage drop is:

. An: approximate expression for the inductance L results: from; the: fact that the change in new meabilitr is independent 0t. direction of the. radio frequency flux. i. a, no linear term ispresent amt the; permeability is a.- iunctioa at current- Theremreassume that.

. Ii==Lo+kiF (2) where. it. is a constant and. 'ithe. instantaneous current. Substituting the above-value. of Lin. (3..)

carts-ski dij/dt (a) It. the current i involves the two. i, 8-, oscillator frequencies, for xample.

* i=a. cos wot-{ b COS-lost V v then the detection terms as obtained from Equation} are.

' F g- 9m sin g iner smg'w zam Since in general the oscillator amplitudefa great ly' exceeds the signal amplitude b, the frequency terms of interest are Zwoiws. Y The magnetic frequency converter according to the 'invention is shown in Fig. 2 to consist of three coupled circuits, tuned to the oscillator, signal and intermediate frequencies. As pointcdyout above; thelntermediate frequency may be chosen as ZGo-Fwsor zany-"we; where 190,05 are the oscillator and signal frequencies, respective- .ly'. To obtainsome'idea asto-the conversion orilci'ency'tcbe expected with such a converter, the circuit arrangement which I' have used will now be'adesc' ribed For conveniencethe signal, oscillator and intermediatefrequencies were chosen as 1700, 2500, 3300 kc. rcspeotively The element values of the three coupled'cir'cuits were r e'adilyl'determined by meansof Fosters reactance theorem Sllchilhflt the network'was anti-f si nal and resonant pointsat 2100 and 2900 kc. The tube T1 which was of the type 6K7 together with tuned circuit I provided a convenient means of introducing the signal frequency w; to the main network. Likewise, the amplifier tube T9 (type 6L6) with tuned circuit 2 served to introduce the oscillator frequency we. The tuned circuit 3 was sharply tuned to the intermediate frequency, the output of which was coupled to one or more intermediate frequency stages IF, followed by a second detector, audio output stage and reprocuit l. An oscillator I2 of conventional design ducer in the usual way. Although ironcore tuning was used for the tuned circuits, the coils and core were all of conventional, design so that little or no saturation effects occurred in these cir-" cuits. On the other hand, .coil L1 was closely wound on a magnetite core having a length of 1 5 inch and a diameter of .160 inch. With this,

large ratio (approximately 6 to l.) of length to diameter, the core is capable of considerable flux concentration.

It should-bepointed out that in this circuit arrangement maximum change in permeability Q, finer magnetite particles are necessary, thereby resulting-in less change in permeability; and necessitating greater local oscillator voltage than in lower frequency applications. The values-M1, M2, M3 in the drawing all corresponded to critical coupling values.

The converison efiiciency of the network is determined by the ratio of 5-1 voltage Eu appearing acrosscoil L3 to the signal voltage E5 across L2 where the oscillator voltage is varied until maximum i-f output is obtained. In making the measurements, since considerable oscillator voltage also appeared across L3, the following method was used to determine the conversion efliciency. With a given signal, the oscillator voltage was varied until maximum output was obtained as denoted by the meter M in the output of the second detector circuit. Then, with the rest of the circuit, except for L3 and output circuit disconnected, the i-f voltage was introduced across 10 until the output meter read the same as 'previousiy. By this means the 5- voltage appearing across Ls could readily be obtained, and the conversion efficiency determined. With a coarse magnetite (-140 mesh) saturating core the measured conversion efficiency was about 20% resonant at 1700, 2500, 3300 kc. with the series experiment. With this arrangement saturation effects occurred in the signal branch of the circuit rather than in the oscillator branch. It was found that with this arrangement practically the same conversion eificiency resulted as in the case where the coil'Lz was the saturating coil.

The circuit of Fig. 3 is generally similar to that of Fig.2 and shows a practical embodiment of the invention as applied to a superheterodyne receiver. Signals picked-up by the antenna I0 are amplified in RF amplifier stage II, the amplified energy appearing in its tunable output ciris connected to the tunable circuit 2. As explained above the sum or difference frequencies are-developed in the L1C1 circuit which contains the s'aturable magnetite core. By way of the couplingcondenser C3 and the coil La the resultingintermediate frequency is transmitted to the circuit 3 which may then be amplified,

.resonant at 1500 and 3000 kc. were as follows:

Li=4 #11. C1: 1960 .mf. La=290 (12:40 mf. 113:2 ph [Ll-if.

With this arrangement the measured conversion efficiency was 12% approximately, a lower value than when the detection was based on the diil'erent frequencies. Disregarding differences in L/C ratios for the two cases, the degree of coupling is less when the frequencies are rather widely separated and hence decreased efficiency results.

With optimum L/C ratios consistent with good circuit Q and a good design of the core and coil to be saturated, the efficiency values given above can be increased to compare more favorably with values obtainable with a tube converter.

It is to be understood that the values above chosen were only by way of example, and that in a particular case the values of the circuit elements L2C2, L101, L3G: of Fig. 2 or 3 are determined such that the network is parallel resonant to the signal oscillator and intermediate frequencies where the oscillator is inductively coupled to the saturable core and coil combination (L1). The networks consisting of L1C1, L201, L303 are equivalent to three parallel resonant circuits but these resonant circuits are not independent of was observed when the circuit 3 was tuned to the intermediate frequency. When, however, very tight coupling to circuit 2 was provided, some output at intermediate frequency did appear.-

Again, the coil L1 was replaced by an air core coil of the same inductance and with the same coupling to the oscillator input coil, but the coil L2 was replaced by a coil plus core of the same inductance value except that the ratio of length to diameter was made the same as in the first one another but are coupled such that parallel resonance occurs at the oscillator, signal and intermediate frequencies chosen. It will be understood, of course, that other coupling methods and arrangements might be used.

While I have shown preferred embodiments of the invention, it will be understood that modifications and changes may be made without depart- "ing from the spirit and scope of the invention, as will be understood'by those skilled in the art.

What I claim is:

p 1. A magnetic frequency converter for combining the frequencies ofa pair of high frequency sources, comprising a pair of circuits each tunable to the frequency of one of said sources, and a third circuit provided with a saturable magnetic core coupled to each of the first mentioned circuits whereby there is produced in said third circuit an intermediate frequency due to the interaction in said third circuit of the frequencies of the first two circuits.

2. A magnetic frequency converter for use in a superheterodyne receiver comprising a pair of circuits tunable respectively to the frequency of the incoming signal and to the frequency of the local oscillator, and a third circuit provided with a saturable magnetic core coupled to each of the first mentioned circuits whereby there is produced in said third circuit an intermediate frequency due to the interaction in said third circuit of the frequencies of the first two circuits.

3; A system of frequency conversion comprising a first resonant circuit tunable to one radio frequency,,a second resonant circuit tunable .to a second radio frequency, and a third circuit effectively coupled to said first and and second circuits and fixedly tuned to the intermediate frequency resulting from the interaction of the first and second frequencies-said latter circuit being provided with a saturable farm-magnetic core which is instrumental in effecting the frequency conversion. r

4. In a radio receiver of the superheterodyne type, a magnetic frequency converter for combining the frequencies from a signal source and a local oscillator source, comprising a first resonant circuit tunable to the signal frequency, a second resonant circuit tunable to the oscillator frequency, and a third circuit fixedly tuned to the difference frequency resulting from the interaction in said third circuit of the signal frequency and the second harmonic of the oscillator frequency, said latter circuit being provided with a saturable ferro-magnetic core.

5. A magnetic frequency converter for combining the frequencies from a single source and from a local oscillator source, comprising a first resonant circuit tunable to the signal frequency, a

second resonant circuit tunable to the oscillator frequency, and a third circuit fixedly tuned to the sum or difierence frequencies resulting from the interaction in said third circuit of the signal frequency and the second harmonic of the oscillator linear relation exists between the change in peri means for deriving from said network a resultant intermediate frequency.

i 7. In a receiver circuit of the superheterodyne type, a source of signal frequencies, a source of local oscillation frequencies, a network compris ing a coil provided with a saturable magnetite core and a condenser shunting the coil, means for coupling each of said sources to the network wherein the frequencies of said sources are combined, and means for deriving from said network a resultant intermediate frequency.

8. In a receiver circuit of the superheterodynetype, a source of signal frequencies, a first tuned circuit coupled to saidsource, a source of local oscillation frequencies, a second tuned circuit coupled to said latter source, a network comprising a coil provided with a ferro-magnetic core and a condenser shunting the coil, means for closely coupling the first and second tuned cir-- cuits to the network wherein the frequencies of said sources are combined, and circuit means closely coupled to said network for deriving therefrom a resultant intermediate frequency.

9. A system of frequency conversion comprising a network having an inductance provided with a saturable ferro-magnetic core in which a nonmeability of the core and the magnetizing current, means for impressing upon said network oscillations of a plurality of differing radio frequencies, and means for deriving from said network a combined frequency resulting from the interaction in said network of theplurality of differing frequencies.

HUGH L. DONLEY.

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