US2214830A - Combined radio and television antenna - Google Patents

Description

Sept. 17 1940. w CARLSQN 2,214,830

COMBINED RADIO AND TELEVISION ANTENNA Filed April 22', 1939 TELL way 0 INPUT PHI/514172" MAw/A/G-s HECEI V21? LOW 65 Hill]! OJ Suventors Wendell L. Carlson Vernon D. Landon (Ittorncg Patented Sept. 17, 1940 p A UNITED STATES PATENT OFFHCE COMBINED RADIO AND TELEVISION ANTENNA i Wendell L. Carlson and Vernon D. Landon, Haddonfield, N. J assignors to Radio Corporation of America, a corporation of Delaware Application April 22, 1939, Serial No. 269,312

1 1 Claims. (01. 2250-20).

This invention relates to noise reducing anwhich encloses a substantial portion of the tenna systems and more particularly to a simpliantenna down lead transmission line. In such fied arrangement adapted to provide improved a system the capacity of the line to the shield reception within two distinct frequency bands, does not upset high frequency operation be- 5 such as would be required for the reception of cause the capacity is distributed over about one- 5 television and broadcast signals. half wavelength of line.

Among the objects of this invention are the This operation will be better understood from provision of an improvedand simplified noise the following description when considered in reducing antenna system; the provision of an connection with the accompanying drawing.

10 improved system for coupling a broadcast re- Similar reference numerals refer to similar parts "3'0 ceiver, or the like, to a high frequency, or telethroughout the drawing. vision antenna; the provision of a simplified sys- R ferrin o h rawi Fi 1 l rates tem for coupling a low frequency receiver to a an embodiment of this invention for use in conhigh frequency balanced antenna to provide nection with a broadcast receiver adapted to noise reduction without unbalancing the high receive signals in wo separate q cy a es; is frequency antenna; and the provision of an im- Figure 2 illustrates a preferred embodiment of proved antenna which is particularly adapted for this invention in connection with a televsion reuse in such a system. ceiver having facilities for the receptionof nor- One known system for couplingalow frequency Rial-Short and long Wave broadcasts; Figure 3 receiver to a balanced dipole arrangement is that illustrates a modification Of this invention; and "20 in which the low frequency input circuit of the Figure 4 represe the application of s inreceiver is connected "to the center tap of the vention to a coup transformer Which is high frequency balanced input winding. This adapted to be utilized in connection with any arrangement makes necessary the provision of b oadcast receiver. e

a tap or contact on the mid-point of the high Referring to Fig.1, a dipole antenna 5 is con- :25 frequency input winding. Such a tap necessarily ee t0 t e input terminals 1 and 9 of areinvolves an added expense in the manufacture ceiver ll by means of a. twisted-pair transmisof such a coil, and it is, therefore, desirable to sion line I3. Within the receiver, a high freprovide a system which eliminates the necessity q cy p y I5 is Connected to the high of such a tap. quency input terminals 1 and 9. The receiver is -30 Another known system is that in which the balalso p d W a p ir Of low freque cy input anced antenna system is used as a dipole at terminals l1 and IS. The primary 2| of a low high frequency, while for operation at low frefr q n y coupling transformer is connected quencies, a capacitor is connected between the across the low frequency input terminals l1 and receiver input and one or both conductors of the Q. The se n ry Coil Consists of two Sections- '35 antenna transmission line. Obviously, such a The first section, 23, is coupled to the low fresystem does not provide noise reduction for quency primary 2|, while the second section, 25, either low or high frequency reception because is coupled to the high frequency primary l5.

a single coupling condenser ofthis type tends The two secondary d s a c nnected 40 to upset the balance in the high frequency sysin series. A switch 21 is provided by which 40 tem, so that its efiiciency in reducing noise picked the low frequency secondary 23 may be shortup in the transmission line is decreased. The circuited during reception on the high freuse of two capacitors connected to both transquency band. A tuning condenser 29 is conmission lines makes possible morenearly balnected across both of the secondary windings.

anced operation, but it is subject to the disad- The grid of the first stage amplification 45 vantage that the coupling condensers by-pass is connected to the high frequency winding the high frequency signals. 25. The remainder of the receiver is con- In accordance with this invention, therefore, ventional, and is not illustrated. In order to a system is proposed in which a dipole antenna provide a leakage path to ground for static dis- 5 operating at high frequencies is connected charges, and the like, a resistor 3| is connected 5 through a balanced transmission line to the between the center tap or one side of the prireceiver, while for the lower frequencies, the mary winding l5 and ground. The value of this antenna is made to operate as a capacity anresistor 3| is preferably of the order of 1 megohm, tenna by means of a connection from the low freand consequentlyit does not affect the balanced quency input system to a shielding conductor input system. I 55 the transmission line is uniformly distributed along the line, and is substantially equal from the shields to each of the two conductors. The

length of this conductive shield may be, for example, approximately in feet. While the conductive shield does not unbalance the high frequency system, it provides sufficient capacity coupling to the transmission line 13 so that low frequency signals may be received, the antenna functioning as a capacity antenna. While the low frequency system may be operated with a ground connection, to provide noise-free reception in the low frequency bands, a counter-poise 35 is provided, which is connected to the remaining low frequency input terminal I9 in the manner described in our copending application Serial No. 253,908, filed January 31, 1939, and entitled Noise reducing systems. Locally generated noise is picked up on the counter-poise and on the down leads and applied to the primary coil 2| in phase opposition so that the noise-representing currents in the primary are substantially reduced. Voltages induced on the antenna 5 and upper portion of the transmission line [3, which are preferably located in a region free from locally generated noises, are transferred to the conductive sheath 33 and produce currents through the low frequency primary 2| in the well known manner.

The manner in which this invention is particularly advantageous for use in a television receiver is best illustrated by reference to Fig. 2. In order to provide the maximum gain at the ultra high television frequencies, it is desirable to provide a resonant primary circuit at all operating frequencies. Accordingly, a system has been proposed in which any one of a plurality of high frequency primary windings 31 may be selected by a switch 39. This arrangement permits each primary winding to be tuned to that frequency which is most advantageous for the particular operating range to which it corresponds. It is apparent that if the system is utilized in which a center tapped coil is necessary, that such an arrangement would require an additional section on the selector switch 39. This expense would, of course, be in addition to that involved in the provision of center-tapped coils.

In the arrangement shown the conductive sheath or shield 33 makes unnecessary the use of center-tapped primary coils for the television section, and provides a satisfactory antenna for the reception of low frequency broadcast signals and for the reception of the usual high frequency broadcast signals. In such an arrangement, the transmission line 13 is connected to the television input terminals 4 I, 43, while the shield 33 is connected to the input terminal 45 which is the input connection to the usual low and high frequency receiver input system represented by the switch 41, and primary windings 49, 5|. In this instance, a conventional ground connection is shown for reception at broadcast frequencies, although the counter-poise may be used in the manner shown in Fig. 1.

Since the system illustrated in Fig. 2 is particularly adapted for the reception of television signals, particular attention is directed to the antenna which is employed in order to provide'maximum response over a wide range of frequencies. The preferred antenna arrangement consists of a pair of oppositely extending radiating elements 53 and 55, each of which consists of two parallel horizontal conductors a quarter wave long disposed in a vertical plane and spaced apart approximately of a wave length at the operating frequency. The conductors of each element are connected at their inner adjacent ends by a pair of jumpers or conductors 51, 59 which constitute a short transmission line. The spacing between conductors 5'! and 59, and their diameters are selected so that the impedance of the line is approximately 200 ohms. The transmission line l3 preferably has a characteristic impedance approximately equal to ohms, and is connected to the mid-point of the short transmission line 51, 59. It is apparent, therefore that the antenna essentially comprises two dipoles connectedin parallel, and that the impedance, looking in either direction from the point of connection, is approximately 100 ohms, thus matching the impedance of the transmission line l3 to that of the antenna system. If it is desired to provide such an antenna with improved directional characteristics, a pair of reflector elements 6|, 63 may be located in a planeparallel to the plane of the antenna and at a suitable distance to provide the desired characteristics. The distance between the antenna and the reflectors should be approximately of the average operating wave length.

The antenna illustrated in Fig. 2 is particularly useful within the television frequency range since its frequency response is approximately twice as broad as that of a single dipole antenna of simi- 12" lar construction.

In the embodiment of our invention illustrated in the preceding figures, the uniformly distributed capacity coupling to the transmission line has been provided by a conductive shield which encloses a portion of the line. An alternative arrangement is illustrated in Fig. 3, in which a third conductor 65, is included in a portion of the twisted transmission line. While this arrangement may be somewhat cheaper than that shown in the preceding figures, the coupling may not be quite as uniform along the line and its capacity per unit length may be somewhat less.

In each of the preceding illustrations, it has been assumed that the input circuits shown constitute a portion of the receiver itself, or, in the case of Fig. 2, a portion of two receivers. It is frequently desirable to provide a coupling transformer by means of which a receiver having only antenna and ground input connections may be 4 adapted to be connected to a receiver are connected to the outer terminals of the serially connected secondary windings. A capacitor H is connected across the low frequency secondary 13 and provides a shunt path for high frequency currents which are induced in the high frequency secondary. As before, a conductive shield 33 and a counter-poise 35 are connectedto the low frequency input terminals.

W e claim as our invention: 7

1. In a device of the character described, an

antenna, a receiver having at least two input circuits, a transmission line connected between one of said input circuits and said antenna, and means including a capacity element having a distributed capacity to said transmission line cou pling said antenna to the other of said input circuits.

2. In a device of the character described, an antenna, a receiver having at least two input cir cuits, a transmission line connected between one of said input circuits and said antenna, and means including a capacity element coupling the other of said inputcircuits to said'transmission line over a substantial portion of the length of said line.

3. In a device of the character described, a dipole antenna, a receiverhaving at least two input windings, a transmission line connecting one of said windings to said antenna so that circulating currents pass through said winding in response to signal voltages on said antenna, and means including a capacity element having a uniformly distributed capacity to said transmission line coupling said antenna to the other of said input windings. I

l. In a device of the character described, a dipole antenna, a receiver having at least two input circuits, a transmission line connecting one of said circuits to said antenna so that circulating currents pass through said circuit due to the dipole action of said antenna, and means including a capacity element having a uniformly distributed capacity to a portion of said transmission line for coupling said antenna to the other of said circuits with respect to voltages due to the capacity action of said antenna.

5; In a device of the character described, a receiver having at least two input circuits, a dipole antenna, a transmission line connecting said antenna to one of said input circuits, and means including a capacity element having a uniformly distributed capacity to said transmission line connected to the other-input circuit.

6. A device of the character described in claim 5 in which said capacity element is a conductive shield surrounding but insulated from said line.

'7. A device of the character described in claim 5 in which said capacity element is a conductor which is adjacent the conductors of said line and insulated therefrom. I

8. A noise reducing antenna system for operation in two distinct frequency ranges which includes a dipole antenna, an input transformer having at least two input windings, a transmission line connecting said antenna to one of said windings, and a conductive sheath around a portion of said line, said sheath being connected to the other input winding. m

9. A noise reducing antenna system for operation in two distinct frequency ranges which includes a dipole antenna, an input transformer having at least two input windings, a transmission line connecting said antenna to one of said windings, a conductive sheatharound a portion of said line, said sheath being connected to one end of the other input winding, a counterpoise connected to the other end of said winding, at least two output windings, associated respectively with said input windings and connected in series, and a capacitor in shunt with the output winding associated with the input winding to which said sheath is connected.

10. A noise reducing high and low frequency antenna system including in combination a dipoleantenna, a receiver having an input system which includes a high frequency and a low frequency primary winding, said high frequency primary being connected to said dipole antenna by a transmission line, a conductive shield enclosing a substantial portion of said line and comprising a uniformly distributed capacity tosaid line for the transmission of low frequency signals from said antenna, said shield being connected to one terminal of said low frequency primary winding, and a counterpoise connected to the other terminal of said low frequency primary winding. i

11. A low and high frequency noise reducing antenna system including in combination a dipole antenna comprising a pair of oppositely extending elements, each of said elements compris ing a pair of parallel conductors, the conductors of each element being connectedat their adjacent ends by a pair of jumpers, a transmission line connected between the mid-points of said jumpers, a transformer having at least two input windings, oneof said windings being connected to said transmission line, a conductive shield enclosing a substantial portion of said line and connected to the other of said input windings.

12. In a device of the character described, a dipole antenna comprising a pair of oppositely extending radiating elements, each of said elements comprising a pair of vertically disposed, parallel conductors spaced apart approximately onetenth of a wave-length at the operating frequency, the conductors of said elements being connected at their inner ends by a pair of jumpers, and a transmission line connected between the mid-points of said jumpers.

13. In a device of the character described, a dipole antenna including a pair of oppositely extending radiating elements, each of said elements comprising a pair of parallel conductors spaced apart approximately'one tenth of a wavelength at the operating frequency, the conductors of said elements being connected at their inner ends by a pair of jumpers, a reflector comprising a pair of conductors parallel to and coextensive with said elements and spaced therefrom a fraction of a wave-length, and a transmission line connected between the mid-points of said jumpers.

14. A noise reducing antenna system which includes a dipole antenna, a receiver having a plurality of high frequency input circuits corresponding to a plurality of operating frequencies in a high'frequency band, and a low frequency input circuit, a transmission line, selector means, said line being connected between said dipole antenna and said selector means so that any desired one of said high frequency input circuits may be connected to said line, and a conductive shield enclosing a portion of said line comprising 7 a uniformly distributed capacity coupling to said WENDELL L. CARLSON. VERNON D. LANDON.

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