US2365453A - Short wave transmission line balancing system - Google Patents

Description

Dec. 19, 1944.

' P. ,F. BY'RNE SHORT WAVE TRANSMISSION LINE BALANCING SYSTEM Original Filed March 22, 1959 SNN Mmm.

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Patented 'Dec. 19, 1944 SHORT WAVE TRANSMISSION LINE BALANCTNG SYSTEM Paul F. Byrne, West Caldwell, N. J., assignor to Federal Telephone and Radio Corporation, a corporation of Delaware Original application March 22, 1939, Serial No.

263,367. Divided and this application November 28, 1941, Serial No. 420,795

6 Claims. ,(Cl. Z50-17) or frequency multiplier grounded on one side, to y two or more symmetrical loads, for example, radiating antennae. This type of arrangement is particularly useful for supplying energy to transmitting antennae which may be used for defining a beacon course, since under these circumstances it is desirable that the load be properly balanced in order that the system be efficient and a, suitable radiation pattern be secured. Furthermore, in beacon systems it is often desired to separately adjust the power fed to each of the radiating antennae, so that the course line may be A properly defined and maintained. Similarly it may be desired to connect two or more balanced lines over which energy is transmitted to a single unbalanced line or to a single balanced line.

It is an object of my invention to provide a radio frequency transmission system which is suitable for intercoupling two or more balanced lines and an unbalanced line.

It is a further object of my invention to provide a radio transmitter in which energy from an unbalanced source is applied to a plurality of antennae each connected to a separate balanced line.

It is a further object of my invention to provide in a radio transmitter a system which permits the independent adjustment of energy to the separate balanced antennae.

It is a still further object of my invention to provide the combination of a radio frequency fsource, a, balanced amplifier and a plurality of ,balanced loads lconnected to the output ofv the amplifier.

It is a still further object of my invention'to provide a radio transmitter with a balanced line rfeed for two or more separate antennae, in which the'en'ergy fed to the antennae may be sepa- 'rately modulated or keyed.

.a pair of symmetrical radio beacon antennae.

" The above mentioned and 'further features and 55 `1, impedances whereas impedance ||2 is a condenser. A balobjects of my invention and the manner of attaining them will be apparent from a .particular description of my invention made in accordance with the accompanying drawing, in which Fig. 1 illustrates a preferred embodiment of a radio transmitter made in accordance with my invention,

Fig. 2 illustrates a form of split stator con'- denser suitable for use in the modulation sys-` tem of Fig. l, and

Fig. 3 illustrates an alternative modulation system in accordance With my invention which may be used in place of that disclosed in Fig. 1.'

Turning now to the drawing and particularly to Fig. l, |00 represents a source of radio frequency energy which may be, for example, an oscillator or a frequency multiplier. In source |00 at |02 is indicated a` vacuum tube which may represent the last stage of the radio frequency circuit within |00. The anode of tube |02 is connected to a positive voltage supply as indicated, and is connected through the primary of transformer |03 to ground for radio frequencies through the radio frequency condenser |0|. Transformer |03 is designed for high frequencies and constitutes a single turn for the primary and secondary so that the coupling between the primary and secondary is made by means of a distributed inductance and capacity only. Coupling transformer |03 is made adjustable so that the coupling between the windings may be varied.

The secondary of the transformer |03 is connected to ground on one side and on the other side to a transmission line |04, through a variable power controlling condenser |05. It is evident that this arrangement forms an unsymmetrical line portion. This unsymmetrical line is connected to a push-pull amplifier comprising vacuum tubes |06, |01. Since, `in order for the vacuum tubes to operate properly in push-pull the input thereto should be balanced, I provide a network `to achieve this balance indicated generally at |08. At lower radio frequencies balanced input may be obtained by merely grounding the center point of a transformer and connecting the outer ends through lines to the grid.

However, at higher frequencies balance cannot be obtained so simply. A balance may be obtained by connecting in series across the line a pair of impedances such as H0, ill, and connecting these impedances to ground through a third impedance ||2. In the circuit shown in Fig. ||0 and are inductances,

ance may be obtained in this way provided imimpedance values of |I2 and H0, |I| being permissible. for most applications. In order that a complete balance may be obtained inductances I I 9 and I I I are arranged so as to have very little,

if any, mutual coupling between them. A blocking condenser I I3 is provided between inductance I I I and the junction points of I l and I I2, so that power may be supplied to the grid of tubes |06 and |97 through the leads I I4, H4' independently of each other. This arrangement permits the use of separate grid meters to indicate the operation of the tubes. The output circuit of the Vacuum tubes |96, |'|,is connected toa high frequency 'variable transformer ||5, the primary of which is connected to a power supply throughv radio frequency cho-ke I I6. Tuning condensers II'I are provided toY tune the output of push-pull ampli- Iier. Coupled to the secondary of transformer I I are conductors |I8, II9, which. together form a balanced output line. The separate conductors IIB, IIS, are unbalanced with respect to ground so that each co-nductor may be consideredy as a further unsymmetrical line. The midpoint of the secondary of transformer ||5 is grounded so that in effect each of lines I |8 and I I9 may be considered as an independent unbalanced line with a ground return. In lines ||8, IIS., are provided variable condensers |20, I2I which may serve to independently control the power output over the respective lines. v

In line I I8. is provided another high frequency network which serves to produce a balanced output from the unsymmetrical line ||.8. This net- Work comprises inductance, elements |22, |24,

connected similar to inductance elementsy HIL;

and lII, and to a variable condenser unit, |26, corresponding to ycondenser ||2. Condenser |26 is made variable so thatitsimpedance may be adjusted to balance, precisely ,transmission line |23. Similarly, line ||9 isV branched to form a balanced transmission line` |29, through av network comprising inductance elements |23, and |25, and a variable capacity element |21.

It is thus evident that the balanced line comprising conductors IIS and |I9 sulpplie's energy to two other balanced lines |28 and I 29 respectively, balanced line |28 being connected to conductor I I8 and balanced line |29 being connected to conductor 9.

To the outer end of transmission line |23 is coupled an antenna |30, shown as a dipole antenna, and to line |29 is coupledanother dipole antenna |3I. While I have shown antennae |39 and |3I, as dipoles, it shouldbe distinctly understood that they may be of any desired form so long as they are designedto form a balanced load. Furthermore, it is clear that instead of leading to antennae, transmission lines |28 and |29 may lead to any desired type of symmetrical load.

If it is desired to use antennae |39 and |3 as a radio beacon, these 'antennae should be arranged at a suitable angle with respect to each other to produce the desired wave pattern. Arrangements of antennae for radio beacon transmission are well known so no specific illustration thereof is made in this application.

In order that the signals from the separate antennae may be distinguished, I provide means to modulate the energy fed to the antennae to form the distinctive signals. Any desired modulating means may be used as the method of modulation in such as to preserve the symmetry of the system. In-the arrangement according to Fig. l, I provide, for modulating the antennae, a lter, comp-rising resonant quarter wavelength framesv |32 and |33 constituting sections of transmission line and loosely coupled to the transmission line. These frames are coupled to the transmission line inductively primarily through capacitive induction and may be precisely tuned by means of trimming condensers |34, |35. When these frames are properly positioned with respect to the transmission line and accurately tuned, they will operate to substantially stop all of the energy from flowing along the transmission line. Although I have illustrated these tuned coupled sections as openended frames, they may have other forms, such as closed frames of proper length or may be of various other formations. For structural details of the various forms of transmission modifying networks, reference may be had to Patent No. 2,159,648, issued May 23, 1939 on an application of Andrew Alford, Ser. No. 162,853 led September 8, 1937. Since the filtering action of coupled transmission line sections, such as shown at |32 and |33 are very critical with tuning, their effect on the flow of energy through transmission lines |28, |29, may be modified by slightly detuning the section. rl'his fact is made use of in vproducing the modulation of the energy transmittedto the antennae. Across each of networks I32, |33, I provide split-stator condensers |36, |31. These condensers are arranged with the Xed plates coupled to the separate conductors of the transmission line, while the rotary plates are driven at a uniform rate by means of a motor |40 or other means. condensers |36 and |31 may be made with a diierent number of notches in the stator plate so that the energy il'owing along transmission lines |28, |29 is interrupted at a diiierent rate to impress a difvferent modulation upon the energy radiated from antennae |39, |3I.

One form of split-stator condenser suitable for use in the system of Figure 1, is illustrated in Figure 2.. This condenser comprises xed toothed' stators 23|, 292, connected to the opposite side of a balanced line 299, and. a. single iotary plate element 233. at a uniform rate the tuning of the condenser is varied periodically, depending upon the speed of the rotor 233 and the number of teeth on stator plates 23|, 232. Thus a chopping or keying of energy may be accomplished by means of this rotary condenser connected across a tuned frame such as I 32. The frequency of modulation may be Varied by varyingthe number ofv teeth on the condenser or by driving the rotors of the condensers at different speeds; The percentage or depth of modulation may be controiledby so choosing the condensers as'toprovid'e` the desired preciseness of tuning of the coupled sections.

While in Fig. 1 I have illustratedV the arrangement wherein an amplier is utilizedbetween the source of radio frequency oscillation and the load, it should be distinctly understood that this amplier may be omitted, and the energy and amplication taken care of in other parts. of

When 293 is rotated the circuit, if desired. Also, it should be understood that the balancing network need not be composed of two inductances and a single capacity as shown, but may be of any form of impedance so long as they satisfy the requirement specified above. 1t is thus clear that in place of inductances lli] and of |08, equal capacities could be substituted therefor and an inductive reactance used in place oi condenser ||2. However, I prefer to use the inductance arrangement since it permits separate energization of the grids. Similarly, the impedance element in the network associated with the separate antennae circuit could be of different values if desired without altering the scope of my invention. It should further be understood, according vto the general reciprocity theorum, that instead of a transmitter, the system may constitute a receiving arrangement. Antennae |30, |3| receive radio signals and transmit them over balanced lines to an unbalanced receiver. In Fig. 3, I have illustrated an alternative form of modulating system which may be substituted for that illustrated in Fig. l. In this arrangement 320,

32|, 3|8 and 3|9, represent the power adjusting condensers and the conductors of the transmission line similar to that disclosed in Fig. l. Similarly the network comprises inductances 322, 324 and capacity 326, and inductances 323, 325, capacity 326', correspond to similar elements in Fig. 1. Loads 330, 33|, may be antennae corresponding to |30, |3| or any other form of symmetrical load. The modulating system, however, differs from that shown in Fig. 1. At 34|, 342 are illustrated two half-wave length short circuited `frames connected at the proper point across balanced transmission lines 328, 329, respectively. At a point midway of the length of transmission line sections 34|, 342 are provided short circuiting switches 343, 344, which are driven by means of a motor 340. Adjustable short circuiting bars 345, 346, are provided respectively on the sections 34|, 342.

This modulating system operates as follows: When a short circuiting switch 343 is crosswise so as to short circuit the network 34|, this network forms a short circuited quarter wavelength line connected across transmission line 328. Aside from resistance and radiation losses the circuit will not drain nor hamper flow of energy along transmission line to load 330. When switch 343 is turned to the open position the effective circuit from the transmission line eX- tends out to the short-circuited end of the halfwavelength section 34|. This then constitutes a half-.wavelength short circuited filter across the main line preventing substantially all of the energy from flowing to the antenna. Thus thc modulation may be obtained by interrupting the flow of energy along the line by means of the short circuiting switch 343. Similarly modulations may be effected in the energy of line 329 by short circuiting switch 344. These switches may be provided with a plurality of segments so as to interrupt the ow at different rates in the two different lines so as to provide different modulations of the energy for the two loads. If it is desired to utilize less than 100% modulation, short circuiting bars 345, 346 may be changed in position so as to alter the length of the sections from that of a full half-wavelength.

While I have described my invention with references to gures illustrating a preferred embodiment thereof, it should be understood that this description is merely by way of illustration and not a limitation of the scope of my invention, which is defined in the accompanying claims.

What I claim is:

1. A high frequency transmission system comprising three balanced lines each having two conductors balanced with respect to ground, a first of said balanced lines having its midpoint grounded, and the second and third of said balanced lines each having a pair of reactances of the same sign connected in series between its two conductors and a reactance of opposite sign connected between ground and the junction of the two series-connected reactances, one conductor of the first balanced line being connected to one of the conductors of the second balanced line at the point of juncture with one of said reactances of the same sign, and the other conductor of said rst balanced line being connected to one of the conductors of said third balanced line at the point of juncture with one of said reactances of the same sign.

2. A system according to claim 1 in which each of the series-connected reactances is an inductance and each reactance of opposite sign is a capacitance.

3. A system according to claim 1 in which the two series-connected reactances of each of the second and third balanced lines are of equal magnitude.

4. A system according to claim 1 in which the rst balanced line is supplied with energy from the output of a pair of vacuum tubes connected in push-pull relation, the output of said tubes being coupled to the first balanced line by a variable coupling means.

5. A system according to claim 1 in which a power adjusting reactance is connected in each conductor of the rst balanced line for independently transferring energy to the second and third balanced lines.

6. A system according to claim l in which balanced antennae are respectively connected to the ends of each of the second and third balanced lines remote from the iirst balanced line, y

and modulating means balanced with respect to ground is connected in each of the second and third balanced lines.

PAUL F. BYRNE.

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