US2401575A

US2401575A - Directional radio transmitting system

Info

Publication number: US2401575A
Application number: US466245A
Authority: US
Inventors: Mark L Macadam
Original assignee: RADIO IND CORP
Current assignee: RADIO IND CORP; RADIO INDUSTRIES Corp
Priority date: 1942-11-20
Filing date: 1942-11-20
Publication date: 1946-06-04
Anticipated expiration: 1963-06-04

Description

June' 4, 1946. l

M. l.. MacADAM DIRECTIONAL RADIO TRANSMITTING SYSTEM Filed Nov. 20, 1942 ggg l Patented June 4, 1946 UNITD STT S ATEN E DIRECTIQNAL RADIO TRANSMITTING SYSTEM Application November 20, 1942, Serial N o. 466,245

2 Claims. 1

This invention relates to a radio transmitting system employing two directional transmitting antennas suitably spaced apart and disposed parallel to each other on suitable fixed supports whereby a marked directional effect in the direction of the antennas or in any desired direction within a certain angle on either side of the azimuth of the antennas may be readily secured. It is a feature of the invention that the direction in which the signal energy is propagated may be readily changed without disturbing the conductors of which the antennas are composed.

In the illustrated embodiment of the invention, the antennas are rhombic antennas of the same size and similar in construction. When two such antennas are supplied with signal currents in such a manner that the current in one antenna is in phase with that in the other, the radiation elds of the antennas combine to produce a main resultant field which is markedly directional and extends in the azimuth of the antennas and in the sense toward which the antennas are directed. It has been found that if the phase of the current in one antenna is shifted slightly with reference to that in the other antenna, the resultant main radiation eld may be shifted to either side of its original or center position depending upon the direction of the phase shift. It is a feature of the present invention that a control means is provided for securing such a shift in the resultant main radiation field with the result that the radiation eld may be directed exactly in the azi-- muth of the antennas or exactly onto a desired region lying Within a number of degrees on either side of said azimuth. It has also been found that the control means provided is effective even though the two rhombic antennas are not exactly similar in size and construction or if the transmission lines connecting the antennas to the final amplifying stages of the transmitter are not exactly similar; these variations in the two antenna paths being compensated for by shifting the phase of the current in one antenna with reference to that in the other by a suitable amount by means of the control means provided.

'When it is desired to transmit a powerful radiation eld to provide coverage over a distant territory, it is necessary to supply the antennas with considerable power as, for example, fifty kilowatts. The radio signals to be transmitted are built up to such a high power level by amplifying them in a plurality of vacuum tube amplifiers connected in cascade, such series of amplifiers comprising several intermediate amplifiers which amplify the signal' at low power levels and driver and final amplifiers which utilize high` voltages and operate at high power levels. It is a characteristic feature of the present invention that the phase shift is secured by means of a device connected with the input circuit of one of the intermediate amplifiers where the power level is low. This arrangement contributes to the safety and convenience of operation of the system in that the operator of the control device, which effects the phase shift, is not exposed to the high voltage and currents which he otherwise would be ifV the phase shifting device were connected to one ofthe transmitting lines connecting the final high power amplifier to its antenna. Furthermore, the desired arrangement reduces the cost of construction substantially over what it would be if the control device were operated at a high power level where its parts would necessarily be massive to carry the heavy currents and would also have to be highly insulated.

Further objects of the invention will become apparent as the description thereof proceeds. For a better understanding of the invention reference is made to the following description taken in connection with the accompanying drawing, in which;

Fig. 1 is a schematic circuit arrangement of a directional radio transmitting system embodying the invention; and

Fig. 2 is a map of a portion of the earth in oblique azimuthal projection showing also approximate directional characteristic patterns adapted to be produced by the transmitter shown in Fig. 1.

Referring to the illustrative embodiment of the invention shown in Fig. 1, I0 denotes a crystal controlled vacuum tube oscillator, I I an intermediate ampliiier, I2 a modulator in which the amplified carrier currents are modulated in amplitude by the speech, music or other signals tol be broadcast, and I3 an intermediate amplifier in which the modulated radio frequency signal cur--` rents are amplified. From the output of I3 the amplified signal currents are transmitted to a pair of rhombic antennas I4, I 4 through the paths I5 and I6. The antennas I4, I4 are disposed parallel to each other at thel desired azimuth and are spaced apart a suitable distance from each other to secure the desired resultant main radiation eld pattern. Each antenna is suitably supported in a stationary position on poles and may be constructed to transmit a large amount of power as, for example, 50 kilowatts.

Circuit pathf |15 is shownas comprising a variometer Il, an intermediate amplifier I8, a pair Variometer I'I is illustrated as comprising a xed winding 22 and a movable winding 23 which` is rotated by a shaft 24 provided with a control knob 25. Shaft 24 carriesa graduated dial 25, a suitable stationary index mark 21 being provided to indicate the dial reading. As illustrated dial 25 is preferably graduated in degrees oi true bearing of the main resultant radiation eld of the two antennas I4 and I4. For monitoring the separate elds radiated by the antennas, a pair of

monitor pickups

28, 28 are provided, one disposed in front of each antenna, the outputs of these pickups being transmitted to a phase monitor 29 of known type by a line 3B, the monitor indicating the phase difference between the'currents received on the pickups.

Assuming that it were desired to broadcastto either Buenos Aires or Rio de Janeiro from a transmitter located at Scituate, Mass., the similar rhombic antennas would be mounted so that they were directed in the direction OA, Fig. 2, to a region or point A midway between these cities. Ii the several elements of circuit path I5 are exactly similar to those of circuit path I6 and antenna I4 is exactly similar in size and construction to antenna I4', no correction need be applied by the variometer I1, since the currents supplied to amplifiers I8 and I8 will be inV phase as will! also the currents in antennas I4 and I4'l so that the resultant main radiation iield of the two antennas will be directed exactlyat point A. If, however, the circuit paths I5Y and I5 are not exactly balanced as, for example, transmission line 2I being slightly diierent in length or construction from transmission line 2|', or antenna I4 being slightly diierent in size or construction from antenna I4', thenl the signal currents in antennas I4 and I4 will not be in phase and the resultant main radiation field will not be directed exactly to point A but to a region on one side or the other of this point. This unbalance between the circuit paths I5 and I6 will be indicated on the phase monitor 29 and may be compensated for by the operator adjusting the control knob of variometer Il. This adjustment will make the current supplied to amplifier IB lead or lag that supplied to amplifierV I8 by the amount necessary to cause Athe azimuth of the main resultant radiation field to be moved in the direction oi point A until the desired coverage is secured. y

Ifrnow-'it is desired to broadcast to Buenos Aires in Spanish, the control knob 25 is rotated inV such direction'for example, as to cause the current supplied to amplier I8 to lag that supplied to amplifier I8. This causes the current in antenne.' I4 to lag that in antenna |47', the amount Yof the lag being indicated on'the phase monitor 29 and .causes the azimuthV of the resultant radiation eld to be shifted inthe direction of Buenos Aires. Such shifting may be continued until the directionhas been shifted `through an angle of A 4 the order of 10 degrees before the two antenna elds get so much out of phase with each other that they start to separate and no longer reinforce each other. 'I'he phase shifting device shown thus provides means whereby the resultant main radiation field may be directed exactly in the direction of Buenos Aires as indicated by curve B, Fig. 2, and the desired region covered in a Spanish broadcast. The dial 26 of the Variometer may be calibrated, as shown, in degrees of true bearing of the resultant radiation eld so that the operator may readily direct the eld in the desired direction or it could be calibrated in terms ofridegrees scanning of the radiation lield.

If it is later desired to transmit a broadcast in the Portuguese language to Rio de Janeiro, it is only necessary for the operator to adjust the control knob 25 in the opposite direction until the phase of the signal current supplied to amplifier I 8 leads that supplied to ampliiier I8 by the necessary amount, as determined by the reading of phase monitor 29. The resultant main radiation eld'will then be directed towards Rio deJaneiro as illustrated by curve C, Fig. 2, and the broadcast may proceed in the usual manner. While the phase shifting device I'I has been illustrated as a variometer, it will be understood that a variable capacitive device or other known type of phase shifting network may be used instead.

I have described what I believe to be the best embodiments of my invention. I do not wish, however, to be conned to the embodiments shown, but what I desire to cover by Letters Pattent is set forth in the appended claims.

I claim:

l. A radio transmitting system comprising, in combination, two similar spaced rhombic antennas disposed at substantially the same azimuth, two circuit paths connected to corresponding ends of said antennas and each comprising a plurality of vacuum tube ampliers connected in cascade, and a control device connected to the input of an amplifying stage preceding the final stage of one path,V said control device being adjustable to vary the phase of the amplified signal current in one antenna with reference to the phase of the amplified signal current in the other antenna during transmission to thereby vary the direction of transmission of the resultant radiation eld of the two antennas and means connected to the first amplifying stages cf said circuit paths forV supplying the signal currents thereto, said final amplifying stage operating'at a high power level and the amplifying stage preceding the nal stage operating at a low power level.

2. The method of transmitting radio frequency signal currents simultaneously from two spaced similar rhombic antennas disposed at substan- Y tially the same azimuth which comprises the steps `while operating the amplifying stage preceding saidfinal stage ata low power level and operati--v high power level. Y

ing the nal stage at a Y Y MARK L. MACADAM.