US1725433A - Band-receiving system - Google Patents

Description

Aug. 20, 1929. F. K. VREELAND BAND RECEIVING SYSTEI.

Filed Aug. 1. 1927 2 Sheets-Sheet l OUTPUT 9 Aug. 20, 1929. g, K, REELAND 1,725,433

BAND nncmvme SYSTEM Fild-Aug l, 1927 2 Sheets-Sheet 2 o o I INVENTOR Patented Au 20, 1929.

UNITED STATES.

PATENT OFFICE."

FREDERICK K. VREELAND, OF MONTCLAIR, NEWdERSEY,

ASSIGNOR '10 VREELAND CORPORATION, OF NEW YORK, N, Y., A CORPORATION 01 NEW JERSEY.

BAND-RECEIVING SYSTEM.

Application filed Augult 1, 1927.

The invention herein described relates to a system of receiving alternating currents including a band of frequencies, particularly such a band of frequencies as comprise the 5 transmission band of a modulated signal wave.

The general purpose of the invention is to receive the component frequencies ofsueh a band with such uniformity as to avoid material distortion of the modulated wave, and to exclude frequencies outside of the band which the system is designed to receive. Another purpose of the invention is to provide means for shifting the position of the band in the frequency scale at will, by a simple adjustment, so that the system may be readily adapted to receive modulated waves of any desired carrier frequenc including the'side bands of such modulat waves. A particular object of the present invention is to secure the band characteristic in a single unit of a receiving or amplifying system, such unit iving substantially uniform reception for all requencies Within the band for which it is designed, with a sharp cut-off for frequencies outside the desired band, thereby securing in a single unit of the system a high degree of selectivity without distortion of the modulated signal wave. In one embodiment :1 of the invention the band selector unit is combined with an antenna or other collector, and a compensating reactance is employed to compensate the indeterminate reactance introduced by the collector and preserve the necessary symmetry of the system. Other features of the invention relate to the combination of a plurality of such units, each having a band characteristic, in a receiving and amplifying system, giving a high degree of amplification over a band of frequencies with a high selectivity or power of excluding frequencies outside the desired band. Other desirable features of the, invention are explained at length.

en selectivity, or the power of separat ing a signal wave of one carrier frequency from undesired waves of different carrier frequencies, is accomplished by the usual method employing a tuned circuit or circuits, the

frequency characteristic of sentially peaked, since there is only one frequency at which the capacity and inductanee reactances of the circuits are balanced. At any other frequency there be an 1 'nously tuned circuits result of this property,

and

the receiver is es- By the use of Serial No. 209,650.

balanced reactance in the system which cuts down the response to such frequency. In receiving a modulated wave, comprising a band of frequencies, such a system will receive one frequency of the band effectively, and the other frequencies of the band less effectively or not at all, with resulting signal distortion.

In the case where a plurality of synchrocade, selectivity isincreased since theamplification at peak frequency is increased in geometric ratio and the amplification at any other frequency is increased in a muc 1 small er ratio, but this selectivity is necessarily secured at the expense of tone quality, since the side bands are relatively reduced according to the same law. It has beenpurposed to improve the reception of' side bands by introducing damping into the synchronously tuned circuits, but this only results in partial mitigation of the distortion and this mitigation is gained at the expense of selectivity.

In my Patents Nos. 1,666,518, April 17, 1928 and 1,682,874, September 1928 and application Serial No. 123,619 I have described means whereby substantially uniform reception is obtained at all frequencies included in the band of a modulated wave, the means specifically claimed in these patents and application being the use of successive stages of amplification having different frequency characteristics, and in combination producing a band characteristic.

By means of the present invention I am able to secure a similar uniform band characteristic in a single selector unit comprising a system of reactances so related to each other that they are mutually balanced, not merely at a single frequency, as in the case of the ordinary tuned circuit, but at a plurality of frequencies included in a limited band. At any frequency outside of this band the reactances are not balanced.

the selector unit responds with substantial equality to all the frequencies within its characteristic band, is non-responsive to frequencies outside this band. When the system is suitably constructed, as hereinafter described, the cut-off at the limits of the band is exceedingly sharp. such a selector, unit I am able to secure distortionless reception of the entire band of frequencies included in a modulgted Wave, and effectively eliminate the freare employed in cas-- quencies of interfering waves. Because 'of the sharp cut-off this uniform band reception is accomplished without any loss of selectivity. Comparing the frequency characteristic of my selector unit with that of a pair of selective circuits tuned by resonance it is found that the broadening of. the band over the effective frequency range is accomplished without any increase of the width of the curve at its base, which determines the selectivity of the system.

Any number of my band selector units may be employed in cascade. In one arrangement that is especially effective they may be used for example as coupling units in a multistage amplifier, thus securing increased signal strength and increased selectivity withoutimpairing the uniformity of the band reception and hence without the increased distortion by trimming the side bands which necessarily occurs when geometric tuning is em-- ployed.

The construction of my band selector is so simple, and the means for compensating indeterminate reactances so effective, that complete symmetry or similarity may be readily secured in the several component circuit elements, so that common control means may be effectively applied to the frequency. adjustment.

These features are illustrated and the apparatus employed is fully explained in the accompanying drawings and in the following description. In the drawings:

Figure 1 represents schematically one'of my band selector units, in generalized form.

Figure 2 is a vector diagram showing the relation of the currents in the various parts of the system of Figure 1.

Figure 3 is a typical curve representing the frequency characteristic of one of my band selector units. It shows also for comparison a frequency characteristic of an ordinary tuned circult.

Figure 4 shows a radio receiving system cn'lbodying one of my band selector units associated with an antenna or collecting circuit on the one hand and an, aperiodic amplifying and detecting system on the other.

Figure 5 shows a band selector unit em ployed as a preliminary selector-with a band amplifier.

Figure 6 shows a radio receiving system embodying a plurality of'my band selector units, one being associated with a collector as in Figure 4 and the others being employed as coupling units in a multi-stage radio frequency amplifier.

Figure 1- hows one of-mv band selector. units in generalized form. 'It employs two reactive couples X X each comprising capacity and inductance reactances C L and C L which are preferably balanced at the same frequency and partially balanced at all the frequencies included in the band, combined with a third reactance X which is ances. This third reactance is small in relation to the reactances of the two reactive couples. It serves as a band forming reactance tending to balance the unbalanced portions ofthe two reactive units and renders the system responsive with substantial equality to all frequencies within a band whose width depends upon the relative values of the band forming reactance and the other reactances. For frequencies outside of this band, whether higher or lower than the frequencies included within the band, the unbalanced portions of the reactances of the two reactive couples become greater or less than the effective reactance of X which is hence unable to balance them so that the system as a whole has an over-all reactance which prevents its transmission of currents of such frequencies outside the band; The reactance X may be untuned and either an inductance, a capacitance,.or a mutual inductance, Figure 1 showing the reactance in generalized symbolic form.

In using my band selector units as a frequency selector the impressed electro=motive force may be applied in any suitable way, shown schematically by the electro-motive element E in the diagram, and the output of the unit may be taken off in any suitable way, as, for example, by means of a pick-up coil S coupled to the inductance L as shown. Other specific means of applying and taking off the signal energy are s'hownin Figures 4, 5 and 6.

The operation of the band selector unit -may be more readily understood by reference to the vector diagram Figure 2. Let the currents set up by the impressed electro-motive force E in the three branches X X, and X be 1,, I and I, respectively. These three currents are considered positive when they flow in the direction from the common point a of the branches to the common point I). Since the total current flowing into or out of points a and 6 must be zero, the current I 1n the common reactance X must be equal and opposite to'the ve'ctorsum of currents I and I in the other two branches. This relation is shown bythe vector diagram'Fi'g. 2, (,0 being the phase angle between the currents I, and I This phase angle varies from zero to 180 degrees in the following manner, depending 7 upon the frequency of the impressed electromotive force E.

For' any given band selector there is a critical frequency F,, at which the inductance and capacity. reactances L G and L and C of the branches X and X are balanced in themselves. The overall reactance of the circuit 0,, L L and C, will then be zero, the currentwill be in-phase with the elec;

inaaaas tro-motive force and its magnitude will depend upon the' effective resistance of the system. The currents I and I will then be in substantially opposite phase relation, considered from the junction points a and b, the angle will be approximately 180 degrees, and the current I will be approximatel small.

There is another critical frequency, F at which the unbalanced reactance of the branches X X in parallel is equal and opposite to the reactance of the branch X,. The reactances of the system as a whole are thus balanced if the currents I and I are in phase, the phase angle being zero, in which case I will be approximately equal to the arithmetical sum of I and 1,, the effect of resistance being considered small.

At any frequency between these limits F and F the unbalanced reactance of the branches X and X will lie between the limits 180 degrees and zero, and the current 1 will adjust itself between the limits zero and 21 If the resistance of the system is low and the value of X is sufficiently small in relation to the other reactances, the current I will be substantially constant at all frequencies between these limits.

At frequencies above or below these limits, the combined reactance of the branches X and X will be greater than X or of opposite sign to X,, as the case may be, so that X cannot balance the unbalanced reactances of X and X and the over-all reactance of the system as a whole is large, and this unbalanced reactance will reduce the current in I to a small value. The band selector thus is responsive to and transmits with substantial equality all frequencies included in the band lying between the limiting frequencies F and F and eifectively excludes all frequencies outside this band.

If the resistance and other losses of the system are low, as they are preferably, the cutoff at the limiting frequencies is very sharp, and the frequency characteristic of the band selector unit has the form shown in Figure 3.

The width of the band depends upon the relation of the reactance to the other reactances of the system. Thus if X is an inductance. as shown in Figures 4, 5 and 6, the band width depends upon the relation of this inductance to the inductances L and L If the reactance X is a capacity, the band width is determined by the relation of the capacity reactance of X to the capacity reactance of C or C In the case where the common reactance is a mutual inductance, the relation is similar to that existing in the case of a simple inductance.

In general the width of the band, expressed as a fraction of the mean or carrier frequency, is equal to the ratio of the reactance X to the balanced reactances of the branches zero, the resistance of the system being consldered C t kilocycles and the ratio of L X and X very approximately. Thus when capacity having the value 0,, the band width 1.; 3

mg the value M3, the band width iq i When X is a mutual inductance havc I n I cite a specific example n the case of broadcast reception at a carrier frequency of 1,000 kilo- Iyl cles with a band width of 20 kilocycles, e limiting frequencies, are 1,010 and 990 to L (or C to G las the casemay be) becomes 2 to 100. That Is, L is equal to 2% of L It will be understood that this example is merely illus-. trative, and that the quantities employed may varied over wide limits to suit the particular case in hand.

- The band width may be determined with:

in reasonable limits by choice of the relation withinlimits.

It is of interest to note the relation of the band characteristic of the band selector unit to the characteristic of a tuned selective circuit. Thus if the common reactance X is omitted, the two branches X and X together constitute a resonant circuit tuned to a certain frequency F this being one of the limiting frequencies of the band of the selector unit. The resonance characteristic curve of such a tunedcircuit is shown by the dotted lines in Fig. 3 in its characteristic sharply peaked form.

When the common reactance X, is added to the system the curve takes the band form shown in full lines, the limiting frequenc F corresponding to the natural frequency of the tuned circuit, and the limiting frequency F being below or above this frequency, depending-upon whetherthe reactance X is induc tive or capacitive.

When the reactance X, has a suitable small value in reference to the other reactances, the Widths of the two curves at the base aresubstantially the same, showin that the uniform band reception is achieved without any loss of selectivity, but rather with a noteworthy gain.

It will be noted that the gradient of the cut-off in the band characteristic is much sharper than the slope of the resonance curve, since at any frequency outside the band X becomes a shunt or bypass of small reactance across the then large unbalanced reactance of X and X and so effectively prevents transfer of energy from one to the other. This sharp cut-ofl is a noteworthy feature of the both. Usually X may remain constant/ For example the capacities C C, may be variable condensers of the usual type, preferably equal, and operated by a common control. The band frequency of the system may thus be adjusted to any pointin the frequency scale within the limits determined by the ratio of the maximum and minimum capacities of the condensers. In this case if the reactance X is an inductance of constant value the band width, considered as a fraction of the mean frequency, is constant, being determined by the ratio of the constant inductances.

Similarly if the frequency is adjusted by varying the inductances, as it may readily be, for.example, by inserting similar short circuiting rings or tubes in the inductance coils, the frequency of the band may be adjusted at any point within the limits determined by the greatest and least value of these inductances. In such case if the reactance X is a capacity, the band width, expressed as a fraction, will be constant, whatever the position of the band in the frequency scale.

While the inductances and capacities may both be made variable it is usually preferable to make one pair of reactances, for example the inductances, constant and similar. The

' other pair of reactances which are of opposite sign, e. g. capac1t1ve,1n the case assumed,

are'also preferably made similar and similarly variable. It is usually desirable to makethe band forming reactance X of the same sign as the fixed reactances, thus, if the fixed reactances are inductive, X, will be an .mductance; 1f the fixed reactances are capacitances, X will be a'capacitance. In this case, if X is constant, the band width, expressed as a fraction, would be constantas above explained.

By making X variable as heretofore noted any desired relationof band Widthto the frequency may be secured.

In Figure 4 I have shown one of my band selector units employed. as a frequency selector in a radio receiving system. The reactive couples X and X -and the common .reactance X, are indicated by the same symbols as in the generalized schematic diagram Figure 1. The band selector unit is associated with the antenna or collector A by a primary coil P coupled with the inductance L of the reactive couple X The band selector unit may be associated with an aperiodic amplifying and detecting system, such as the detector D and audio frequency amplifier A 'in any suitable way. I prefer to form this association by an adjustable aperiodic coupling which will give control of the strength of signal impulses applied to the system. A convenient arrangement for this purpose is an aperiodic pick-up coil S which is in variable inductive relation with the inductance L of the band selector. Since the purpose of this coil is to derive from the current in L an electro-motive force which is applied to the detector, tuning or freof interlinkage, the electro-motive force applied to the detector may be varied from 'quency adjustment-is not necessary. It is zero to a maximum. The maximum occurs when the coils are closely coupled, and the minimum when their fields are not interlinked at all.

The antenna coil P is preferabl closely coupeld to the inductance L Uusa ly I prefer a step-up ratio of turns, i. e. the number of turns of the antenna coils P is less than the number of turns of the inductance L,.

In the case of such a step-up ratio the effective capacity introduced into the reactive element X by the antenna is less than the antenna, or in general the effective reactance introduced by the collector, into the reactive element X is an indeterminate factor which if not compensated, would unbalance the symmetry of the system, and, if large enough, would distort the band characteristic. .A feature of the present invention which avoids such unbalance and distortion is the introduction of a compensating reactancg; in one of the reactive couples corresponding'to the indeterminate reactance introduced into the other reactive couple. For example, in the case where the element that introduces the indeterminate reactance is a collector and the reactance introduced by the collector is capacitive, as shown in Figure 4, symmetry may be restored by introducing a compensating capacity C which is shown in parallel with the capacity 0 This capacity may be adjustableto compensating for any desired value of the capacity of the collector, but I prefer tomake it a fixed capacity larger than the largest value of the effective capacity that will be introduced into the element X by the collector. I then employ an adjusting capacity C in parallel with the capacity C to make up the difference between the compensating ca acit C and the effective capacity intro ucecl into the system by the collector. 4

In this'respect the compensation of the collector reactance to make the system symmetrical is similar to the means'of compensation of two tuned receiving circuits shown 582,603, 582,604-680,061 and 680,062, in which I set forth in general terms the means for securing sym'metryor similarity in two parts of a system, one of which contains an indeterminate reactance such as an antenna or other collector. In my applications above mentioned a broad system of compensation was described, and specifically, its application to a receiving system comprising two tuned circuits tuned to the same frequency, by the method of geometric tuning common in the art. In the case of the present invention changed at will without "band character.

similarity in two similar means for producing symmetry or circuit elements, one of which contains an indeterminate reactance, is applied to another specific case, in which similarity is desired in the two reactive elements X X, of my band receiving system.

It will be readily understood that any of the specific devices shown in the above mentioned applications for producing similarity in two circuit elements will be applicable to the specific case of the two circuit elements, one of which includes a collector, in the band selector unit of the present invention.

In the arrangement shown in Figure 4, the position of the band of reception in the frequency scale is determined by adjusting the capacities or condensers C, C, simultaneously by a common control movement, whereby the frequency of the band of reception may be altering its uniform In Figure 5 I show one of my band selector units employed as a preliminary selector, with a coupled collector, in conjunction with a band amplifier of the type set forth in my Patents Nos. 1,666,518, April 17, 1928, and 1,682,874, September 4, 1928, and application Serial No. 123,619. This is a very desirable improvement over the combination including a tuner, set forth in my application 123,619.

By a suitable choice of the inductances and capacities of the band selector unit and the bandv amplifier, the frequency characteristics may be made to coincide so that they may be adjusted in the frequency scale by a common control means, as shown and fully explained in my former application.

Figure 6 shows a-modified arrangement including a plurality of my band selector units, one being employed to :rrnle the collector,

here shown as a loop collector, with the amplifier, the others being emplo ed as interstage coupling elements of a ra io frequency amplifier.

The two band selector units arepreferably made alike, for convenience in mechanical construction. The inductance L of theloop is made approximately equal to that of the inductor L and a small compensating inductor L added, so that all the units are made symmetrical and all may be adjusted by a single control means.

It will be understood however that com.- plete symmetry is not essential, provided there is 'such similarity as will give the various band selector characteristics.

It will be understood that other modifications and applications of the system maybe made without departing from the essential principles of-the invention.

I claim as my invention:

1. In a system for receiving the transmis sion band of a modulated wave, a band selector unit comprising two reactive couples, each having reactances that are partly balanced at the frequencies included in the trans1nission band, and an untuned reactance com.- mon to both couples whose value is so related'to the rcactances of the couples that the units similar frequency balanced and the system is made responsive to all frequencies within the transmission band. Y

2. In a system for receiving the transmission band of a modulated wave, a band selector unit comprising two reactive couples each having reactances that are partly balanced at the frequencies included in the transmission band, and an untuned reactance com-- mon to both couples whose value is small and so related to the partly. balanced reactances of the couples that the unbalanced portion of these reactances is balanced and the system is made responsive to all frequencies within the transmission band.

3. In a system for receiving the transmission band of a modulated wave, a band selector unit comprising two reactive couples, each having reactances that are partly balanced at the frequencies included in the transmission band, and a reactance common to both couples whose value relative to the component reactances of the couples is approximately equal to the ratio of the range of frequencies included within the transmission band to the mean frequency and so related to these reactances that their unbalanced-portion is balanced and the system is made responsive to all frequencies within the transmission band.

4. Ina system for receiving the transmission band of a modulated wave, a band selector unit comprising two reactive couples,

each having reactances which are balanced llQ in themselves at one limiting frequency, and:

a reacta'nce common to both couples having a value equal to the effective unbalanced reactance of the two couples at a second limiting frequency, whereby the system is made responsive with substantial uniformity to all frequencies between these limiting frequen-.

cies including the frequencies of the transmission band.

5. The method of selectively receiving the 7 transmission band of a modulated signal wave which consists in applying the signal energy to a receiving system, balancing the reactances of the system in palrs at one limiting frequency, balancing the unbalanced reactances of the pairs at another limiting frequency by a reactance common to both pairs, thereby receiving with substantial uniformity all equencies in the band included between these limiting frequencies, including the frequencies of the transmission band, and

' rejecting frequencies outside of the limiting frequencies by the unbalanced reactances of the pairs.

6. The method of selectively receiving the transmission band of a modulated signal wave which consists in applying the signal energy to a receiving system, balancing the reactances of the stem in airs at one limiting frequency, ba ancing t e unbalanced reactances of the pairs at another limiting freuency by a reactance common to both. pairs,-

v t ereby receiving with substantial uniformactances of thepairs atanother limitingfreuency by a reactance common to both airs, t iereby'receivin'g with substantial uni ormity all frequencies in the band included between these limiting frequencies, and varying the position of the band of reception in the frequency scale by simultaneously and similarly varying the balanced'reactances.

8. In a system for receiving the transmission band of a modulated wave, a band-selector unit comprising two reactive couples, each having reactances that are partly balanced at the frequencies included in the transmission band, an untuned reactance common to both couples whose value is so related to the reactances of the couples that the unbalanced portion of those reactances is balanced and the system is made responsive to all frequencies Within a definite band, and means for simultaneously and similarly varying the partly balanced reactances, thereby shifting the band of response in the frequency scale while preserving its band character.

9. In a system for receiving the transmission band of a modulated wave, a band selector unit comprising two reactive couples, each having reactances that are partly balanced at:

the frequencies included in the transmission band, and an untuned reactancebridging the common terminals of the two'couples whose value is-so related to the reactances of the couples that the unbalanced portion of these reactances is balanced and the system is made responsive to all frequencies within the transmission band.

10. In a system for receiving the transmisll I sion band of a modulated wave, a band selector unit comprising two reactive couples, each having reactances that are partly balanced at the frequencies included in the transmission. band. anuntuned reactance common to both couples whose value isso related to the the system is made responsive to all frequencies within a definite band, and means for varying the width of the band of'response by varying the magnitude of the bridging re actance.

This specification signed this29th' day reactances of the couples that the unbalanced portion of these reactances is balanced and.

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