US2223547A

US2223547A - Receiving system

Info

Publication number: US2223547A
Application number: US243107A
Authority: US
Inventors: Charles M Burrill
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1938-11-30
Filing date: 1938-11-30
Publication date: 1940-12-03
Anticipated expiration: 1957-12-03

Description

D 3} 1940- c. M. BURRILL 2,223,547

RECEIVING SYSTEM Filed Nov. 30, 1938 7 II F 7 E airy wm B 3nventor Charles- 6 M Burrz'll I attorney Patented Dec.

Delaware Application November so, 1938,

' 3Claims. (aim-20 This invention relatesto radio receiving systems and. more, particularly,

means for reducing .to a method of and fading which is caused by the simultaneous reception of ground and sky waves.

' ,Among the objects of provision ofv means for improvingradio recepthis inventionv are. the

tion; the provision of. means for reducing ground Wave reception in order.

to provide uninterruptedsky wave receptionythe provision of a method 10. for ,adjusting and utilizing, a. directive antenna for the reduction offading;

and the provision of a methodv of receiving radio signals, without disturbances due t nating the constant the. received signal o, selective fading, by elimi-.

ground ,wave component of by an adjustment made in the absence of a sky wave and then utilizing the sky wave for reception.

One well known system; of providing uninterrupted reception of radio signals is the ,so-

called diversity system, in which a plurality of widely separated antennas areprovided and connections are automatically made to the one delivering the greatest signal amplitude at anytime. This system no cost-pr space limitation.

is satisfactory when there is However, it is not practical for general use because of the expense of the number of antennas which are required,

and because a large available. v

1 system of reception is provided which accomplishes the results the expenditure of quired for the usual In practicing my which may, by a of diversity reception with but little more than is rebroadcast antenna.

invention, two antennasmay r. be employed but preferably one antenna'is used.

simple switching system, be a non-directional antenna. "In accordance with this system, the

diversity resides 1 points of reception,

not in the multiplicity of but rather in advantageous for use with home receivers in regions where selective fading or interference from man-made interference is troublesome.

, It is Well known lective fading is int that themajor cause of seerferencev between the ground wave and the corresponding sky wave which is reflected from the ionosphere.

The interference may be reduced by eliminating either the "sky wave or the ground wave.

ognized by earlier sky wave. I have This'has been recinventors, but, .in every infading has been for reducing the H land area is usually not- In accordance with my invention, a

the directional characteristic of. the antenna. Consequently, my system is particularly PATENT" oF ics RECEIVING SYSTEM Charles M. Burrill, Haddonfield, N. J., assignor to Radio Corporation of America, a eorporation of having an antenna receptive. only .to the sky 1'0 'wave from a'.particular transmitter, changes in I the angle and polarization of the sky .wave affect only the intensity of the received-signal whichmay readily be controlled in the .usual manner by an automatic volume control.

- It is also wel1 known that selective fading due to sky wave interference is noticeable mainly. during the hours of darkness. Daytime recep-. tion, especially from local stations, is usually free, from selective fading. I, therefore, propose to 20. utilize the ground wave signal whenever condi,; tions are such that its reception ispossiblewithe out interference from the sky wave, by providing a seperatevertical antenna for use during the daytime, or by providing a switch which'jwill- 25.

, convert the sky wave antenna into aground wave connection with the accompanying drawing. ,Its. 30;

scope is indicated by the appended claims.

Referring to the drawing, V Figure 1 is a schematic illustration of an 8111- bodiment of my invention utilizing a loop anh a; 3'5

Figure 2 is a schematic illustration of analternative embodiment of my invention utilizing adipole antenna; and I r Figure3 is another embodiment utilizing a horizontal loop and a separate ground wave antenna. V

7 Referring to Fig. l, a loop nected through a transmission pling transformer 1 to a receiver 9.

antenna 3 conline 5 and a cou- The loop.

antenna 3 is adjustably mounted so as to be rotatable about its horizontal and vertical axes.

Inorder to explain the directive'operation of such an antenna, I have shown a transmitter Ifll radiating waves which travel'to the receiving loop directly and also after ionosphere. The reference numeral 13 representsa vertically polarized ground wave having a vertical electric vector E and a horizontalmag netic vector H, at right angles thereo. In different-localities the orientation of the. ground,

reflectionfrom the 5 f wave vectors may vary somewhat from the orientation shown. The direction of propagation of the wave is at right angles to both vectors, as indicated by the arrow [5. It is well known that the plane of polarization contains the electric vector and is parallel to the direction of propa gation. This plane may be rotated by the reflection from the ionosphere. The direction from which the sky wave approaches the receiving loop is different from that of the ground wave. The sky wave I"! is shown after reflection. The electric vector E is horizontal and the magnetic vector H is at right angles thereto and perpendicular to the direction of propagation, which is represented by the arrow IS. The rotation of the plane of polarization is not necessarily 90",- as illustrated. This angular rotation has been assumed for convenience of illustration.

A loop antenna, such as that shown at 3, is known to have directional properties which depend on the polarization of the signals to be received. Reception is a maximum when the plane of the loop is parallel to the plane of polarization, and is a minimum when at right angles thereto. It is evident, therefore, that an orientation of the loop which effectually eliminates the ground wave signal l3, that is, an orientation with the loop plane perpendicular to the plane of polarization of the ground wave, does not eliminate the sky wave with a rotated plane of polarization. This effect is well known in directional compass work in which a false bearing is frequently obtained by reason of sky wave reception at the ground wave null point.

By adjusting the loop antenna 3 about its vertical and horizontal axes to eliminate the ground wave signal during daylight hours, when there is no sky wave present, a true ground wave null is obtained, that is, the null is due entirely to the directional properties of the loop antenna with respect to the ground wave and not due to a particular phase relation between the ground and the sky wave signals. This adjustment cannot satisfactorily be accomplished at night for the reasons noted above. Consequently, having adjusted the loop antenna to eliminate the ground wave signal from a particular transmitter, night time reception is accomplished by utilizing only the sky wave sig nal, thus completely avoiding selective fading difiiculties.

To provide satisfactory day, it is necessary to provide another antenna or to minimize the directional properties of the loop. This may be accomplished, for example, by a switch 2! which is connected between the primary and secondary of the coupling transformer 7 through a capacitor 23. By unbalancing the system, in-phase currents, picked up by the lead-in 5, and the loop antenna 3, acting as a capacitive antenna, are coupled to the receiver. By operating the switch 2|, ground wave or sky wave reception may be selected at will.

While I have shown a loop antenna in connection with Fig. 1, any antenna having the desired directional properties may be employed. In Fig. 2, I have illustrated, by way of example, the use of a dipole antenna 25. The dipole antenna has this advantage over the loop antenna: it may be adjusted to eliminate the ground wave and yet still receive the sky wave even if the plane of polarization of the sky wave is the same as that of the ground wave. With the loop antenna, the planes of polarization of reception during the 1 the two waves must not be parallel, that is, one must have been rotated, or both waves will be eliminated together.

The pickup of the dipole is a minimum when the dipole conductors are parallel to the direction of propagation of the wave. Therefore, when the dipole is so adjusted as to eliminate the ground wave, the sky wave may be received, whether its plane of polarization has been rotated or not, because of its different direction of propagation. The pickup of the dipole is also a minimum when the dipole conductors are perpendicular to the plane of polarization of the wave. When so adjusted to eliminate the ground wave, the sky Wave may be received only if' its plane of 'polar'mation has been rotated.

In Fig. 2, the dipole antenna is coupled to the input of an amplifier 2! by means of transformer l, as before. In-phase currents from the antenna and lead-in are coupled to the receiver by means of a center tap connection from the primaryof transformer 1 to the primary of a second transformer 29. The secondary of transformer 29 is coupled to-the input of a second amplifier tube 355 whose plate is connected to the plate of. amplifier tube 21. A switch 33 is connected so that it will short-circuit the primany of transformer 7. A switch 35 is connected so thatit will short-circuit the primary of transformer 29. By opening switch 33 and closing switch 35, sky wave reception is obtained, while, in the reverse position, the antenna and lead-in function as a capacity antenna to receive the corresponding ground wave signals. For convenience, switches 33 and 35 may be operatively connected.

Electrical switching may be accomplished by applying suitable biasing voltages to the tubes 21 and 3i. The biasing Voltages are manually controlled by

switches

43, 45 which, in one position, connect the cathode of tube 21 to ground and the cathode of tube 3| to a source of positive potential 49' for sky wave reception, and, inthe other position, connect the positive bias from battery 41- to the cathode of tube 27, grounding the other cathode, for ground wave reception.

A modification of the directional antenna which is useful in simultaneously reducing the vertically polarized ground wave signals from several transmitters is shown in Fig. 3 in which a loop antenna 31 is adjustably mounted in an approximately horizontal plane. Such an antenna has the'advantage of being equally nonresponsive to vertically polarized signals from all directions in a horizontal plane. Consequently, man-made static, which is usually vertically polarized, as well as ground wave signals from nearby stations, may be reduced, while down coming sky waves may be received from all directions. Ground wave reception is provided by a separate antenna 39 which is connected to the receiver by a switch 4|.

Since the ground wave signal is usually quite intense, in order to provide sufiicient elimination it may be necessary to shield the lead-in conductors, the coupling device, and the receiver The degree of success in'shielding may be determined experimentally by the daytime adjustment, referred to above, in which the ground wave signal is eliminated from the receiver.

signals which comprises adjusting a directional antenna to minimum response to the ground wave during a selective time in which the sky wave is not present, and

receiving only the sky wave signals when they are present, to obtain undistorted reception. I have illustrated several devices by means of which this method may be practiced.

I claim as my invention: c

1. In a receiver for the reception of broadcast signals which includes an antenna system having a normally selective response characteristic and switching means for modifying said response, said system being normally adjusted to reject predetermined ground wave signals, themethod of reducing selective fading due to interference between said predetermined ground wave-signals and corresponding sky wave signals which includes the steps of selectively rejecting ground wave signals and utilizing only the received sky wave signals during periods 1 characterized by the presence of both ground and sky wave signals, and modifying said selec- .tive characteristic to receive ground wave signals during periods in which said sky wave signals do not interfere with reception of said ground wave signals.

*2. In a receiver for the reception of broadcast signals which includes an antenna system having a normally directive response characteristic and switching means for modifying said 7 directive characteristic, said system being normally adjusted to reject predetermined ground wave signals, the method of reducing selective fading due tointerference between said predetermined ground wave signals and corresponding sky wave signals which includes the steps of receiving and utilizingonly sky wave signals during periods characterized ground and sky wave signals, and modifying said directivei-;characteristic to receive and utilize ground wave signals during periods in which said sky wave signals do not interfere with reception of said ground wave signals.

3. In a receiver for the reception of broadcast signals having a directional antenna system and switching means for modifying said directive characteristic, the method of reducing selective fading due to the simultaneous reception of ground and corresponding sky wave impulses, which includes the steps of adjusting said directional antenna system to reject predetermined ground wave signals during a period in which ground wave signals only are present.

utilizing said directional system to receive sky wave signals only during periods characterized by the presence of sky wave signals, and modi I fying said system to receive ground wave signals during periods in which said sky wave signals do not cause selective fading.

I CHARLES M. BURRILL.

by the presence of