US3824599A - Tv/fm/am antenna coupler - Google Patents

Abstract

An antenna system using a standard dipole antenna capable of receiving television, AM and FM signals employing signal isolation means wherein the antenna may be automatically used to receive AM, FM and television signals without adjustment or control. A coaxial cable is employed from the antenna coupler to the AM/FM radio receiver, and a coaxial cable stub is disposed adjacent the radio antenna lead-in and is of a length equal to substantially 1/4 of a wavelength in the FM band, the shields of the antenna lead-in and the coaxial stub being electrically connected, and the inner conductors being connected to the dipole antenna such that the stub coaxial cable functions as a ''''short circuit'''' providing correct coupling to the dipole antenna when receiving FM signals, but does not interfere with AM signal reception.

Description

United States Patent [191 Haswell TV/FM/AM ANTENNA COUPLER [75] Inventor: Charles K. Haswell, Scotts, Mich.

[731 Assignee: Barker Manufacturing Company,

Inc., Battle Creek, Mich.

3/1967 Podell 333/11 2/1973 Zelenz 333/11 X OTHER PUBLICATIONS Noll et al., Television & FM Antenna Guide, The

/2 e I 40$ M30 M66 July 16, 1974 MacMillan Co., N.Y., 1951, pages 53, 73 & 74.

Primary Examiner-Tau] L. Gensler Attorney, Agent, or Firm-Beaman & Beaman [57] ABSTRACT An antenna system using a standard dipole antenna capable of receiving television, AM and FM signals employing signal isolation means wherein the antenna may be automatically used to receive AM, FM and television signals without adjustment or control. A coaxial cable is employed from the antenna coupler to the AM/FM radio receiver, and a coaxial cable stub is disposed adjacent the radio antenna lead-in and is of a length equal to substantially 1/4 of a wavelength in the FM band, the shields of the antenna lead-in and the coaxial stub being electrically connected, and the inner conductors being connected to the dipole antenna such that the stub coaxial cable functions as a short circuit providing correct coupling to the dipole antenna when receiving FM signals, but does not interfere with AM signal reception.

4 Claims, 4 Drawing Figures l TV/FM/AM ANTENNA COUPLER BACKGROUND OF THE INVENTION from an'installation and maintenance standpoint, and

detracts from the appearance of the dwelling.

Recreational vehicles such as travel trailers, campers,

motor homes, cabin cruisers and the like often carry Such a plurality of antennas is expensive, troublesome television receivers and AM/FM radio receivers for pleasure use. The mounting of separate television, AM and FM antennas on such recreational vehicles is particularly expensive, and troublesome, and requires considerable maintenance in view of the exposure to damage of the antennas from branches, and limited clearance under overhanging objects. Television signal receiving antennas commonly employed with recreational vehicles are often of a retractable and elevatable type wherein the antenna is only elevated into a signal receiving position when the vehicle is at rest, and is lowered to a protected retracted position during travel.

In the past, the utilization of a single antenna for receiving television, AM and FM signals has been impractical inthat manual switching from one system to another was required in order to obtain an acceptable signal for the purpose intended. Also, it has not been practically possible to receive acceptable television and AM or FM signals simultaneously for use at separate receivers when employing a common antenna.

In particular, to the inventors knowledge, an antenna coupling system has not heretofore been proposed which would permit a standard TV/FM antenna to be used for AM radio frequency reception, and still retain correct matching for FM radio reception.

SUMMARY OF THE INVENTION It is an object of the invention to provide an antenna coupling system wherein a standard dipole TV/FM antenna may be used to receive television, FM and AM radio frequency signals wherein no manual switching between antenna systems is required, and the coupler automatically provides proper matching and coupling depending upon the signal being received and utilized. It is a further object of the invention to provide an automatic antenna coupler wherein AM and FM radio frequencies may be received by a standard TV/FM dipole antenna and the radio signal usage does not interfere with simultaneous television signal reception and distribution.

It is a further object of theinvention to provide an antenna coupler system employing a common dipole antenna for AM and FM radio receiver use wherein proper coupling for FM signal reception is automatically provided, yet the AM signal and reception is not adversely affected by the FM antenna components.

It is another object of the invention to provide an antenna coupler system which is particularly suitable for use with recreational vehicles employing 12 volt electrical systems wherein the coupler utilizes a housing having terminals connectible to a standard TV/FM dipole antenna, and permits an AM and FM receiver antenna lead-in to be connected thereto, as well as permitting a plurality of television leads to be connected thereto, isolation between each receiver lead-in being achieved. The housing also incorporates a 12 volt socket wherein a 12 volt power supply, such as for a television receiver, may be connected thereto.

In the practice of the invention an AM/F M radio receiver utilizes a coaxial cable lead which is of a low capacity, and consists of an inner conductor, and a concentric conducting shield. A stub of a similar coaxial cable is adjacently disposed to the primary radio receiver antenna lead cable, and this stub is of a length equal to substantially wavelength at I00 Mhz. The adjacent ends of the primary coaxial lead, and the stub, are electrically interconnected, but the outer ends of the coaxial cables are not electrically interconnected. The inner connector of the primary lead is connected to one of the dipole antenna terminals, while the inner conductor of the stub coaxial cable is connected to the other dipole antenna terminal. This relationship permits the stub coaxial cable to form a short circuit between its terminal end and the shield of the primary coaxial lead at FM frequencies and provides a reasonable match between the dipole antenna and the AM/FM receiver for FM reception. In the AM broadcast band, the coaxial stub has no significant effect, and the active element of the antenna lead during AM reception is the primary coaxial cable and the antenna lead-in and the connected antenna element.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned advantages and objects of the invention will be appreciated from the following description and accompanying drawings wherein:

FIG. 1 is a schematic view of an antenna coupler system in accord with the invention,

FIG. 2 is a view of the circuit in accord with the invention,

FIG. 3 is a perspective top and side view of an antenna coupler housing in accord with the invention, and

FIG. 4 is an underside view of the coupler housing of FIG. 3. i

DESCRIPTION OF THE PREFERRED EMBODIMENT The antenna coupler system in accord with the invention may be used with any dwelling, recreational vehicle or enclosure associated with an antenna, and television and radio receivers. While the invention was particularly developed for use with recreational vehicles, its use is not limited to such applications, and the coupler may be readily employed in permanent dwellings,

and the receiver leads associated with the coupler may be built in wherein distribution of the signals may be desired at remote locations in the vehicle or dwelling.

structure such as disclosed'in US. Pat. Nos. 3,587,104 and 3,665,477.

The antenna coupler 12 includes a housing 14 in which a plurality of terminals are mounted upon a printed circuit board 16, upon which is mounted a bifilar wound ferrite core transformer, three resistors and a capacitor. The housing 14 also includes a 12 volt socket 18 exteriorly accessible of the housing.

In FIG. 1 an AM/FM radio receiver is illustrated at 20 having an antenna lead 22. A remote television connection outlet is illustrated at'24, having an antenna lead 26. A television receiver is indicated at 28, having an antenna plug in type plug 30, and a l2 volt power supply connector 32 adapted to be received within the socket 18. In dotted lines a second television receiver 34 is indicated adjacent the remote outlet 24.

The antenna is connected to the coupler 12 housing terminals by a lead 36, which is of the 300 ohm shielded twin'lead type. Likewise, the lead 26 may be of similar or the same construction The coupler circuitry includes terminals 38 and 40 which constitute the input terminals for the coupler, and'are connectible to the conductors of the dipole antenna lead 36. Terminal 38 is connected to the radio receiver terminal 42 through a l50 ohm resistor 44, and terminal 40 is directly connected to the other radio terminal 46.

The bifilar wound ferrite core transformer-48 includes coils 50 and 52, and taps 54 and 56, tap 56 being connected to the conductor interconnectingterminals 40 and 46, and tap 54 being connected to the conductor connected to terminal 38, prior to resistor 44, and in series with lOO pf capacitor 59.

Television receiver lead terminals 58 and 60 are interconnected through a 330 ohm resistor 62, and television receiver terminals 64 and 66 are likewise interconnected through 330 ohm resistor 68. One lead of the coil 52 is connected to terminal 58, while the other coil lead is connected to terminal 60. Likewise, a lead of transformer coil 50 is connected to terminal 64, while the other transformer coil lead is connected to terminal 66.

The dotted line conductors represent lead 26, connected to remote outlet terminals 70 and 72, one of which is grounded. 68 pf capacitors 74 may be employed within the remote television outlet 24 to reduce interference to AM radio by harmonics of the TV scanning circuits when TV and AM radio are used simultaneously.

The AM/FM radio receiver is connected to the coupler 12 by means of a primary coaxial cable 76 which is of a low capacity automotive type cable commonly used with automobile radio antennas. The coaxial cable 76 has a standard co-ax antenna jack 80 at its outer end wherein the central pin 82 of the jack is in series with a 150 pf capacitor (not shown) housed in the jack body connected to the inner conductor 84 of the cable, while the outer contact 86 of the jack is electrically connected to the conventional annular shield or conductor 88 surrounding the cable inner conductor 84, and insulated therefrom. The inner end of the primary coaxial cable conductor 84 is connected to the terminal 42.

A second coaxial cable stub 90 of a construction identical to that of the primary cable 76, is disposed adjacent the inner end of the cable 76, and may be taped to the primary cable, or otherwise mechanically lo cated adjacent the same. The stub 90 includes an inner conductor 92 connected to the terminal 46, and the outer shield 94 of the stub is electrically connected at its inner end 96 to the primary cable shield inner end The length of the stub coaxial cable 90 is approximately $41 of the wavelength of most of the FM radio signals received. Preferably, the length of the stub 90 is exactly A the wavelength of the signal being received. However, as the frequency of the received signal varies as the receiver is tuned, the length of the stub is compromised by making the length 5 of a wavelength at approximately 100 Mhz., which is approximately at the center of the FM radio frequency range for conventional reception.

The housing 14 includes a pair of pin receiving terminals 100 and 102, connected to the circuit board terminals 64 and 58. The remote television receiver 34 lead is likewise connectible to the pin receiving terminals 104 and 106 mounted in outlet 24 connected to the terminals and 72.

The standard antenna 10 used for television and FM reception presents a very low impedance at AM frequencies, and thus this type of antenna has not previously been acceptable for use as an AM- radio receiver antenna. However, due to the use of the stub coaxial cable 90, and the interconnection between the stub and the primary coaxial antenna-cable 76, the stub presents a closed circuit at FM frequencies due to its 4 wavelength dimension, permitting a good impedance match at FM frequencies, and achieving excellent FM reception. At AM radio frequencies, the stub has no signiflcant effect, and only the single wire 84 of the primary antenna cable, and of the antenna lead connected thereto is effective to receive AM frequencies permitting an excellent signal to be received at AM frequencies. The reception received is considerably better than that obtained by the conventional whip antenna normally used for AM radio reception.

The use of the A wavelength stub provides isolation of the outer shield of the co-ax cable to AM reception, but still retains correct matching for FM reception, and thus the multi-purpose of the antenna 10 for TV, AM and FM frequencies is achieved.

The use of the transformer 48 for isolation between a plurality of television receivers is known, and as the signals at each end of the coils 50 and 52 are out of phase an isolation is produced which prevents attenuating effects caused by varying and random lengths of leads between two TV antennaoutlets. The resistors 62 and 68 maintain an impedance match.

The pf capacitor 59 provides some isolation at AM frequencies from the interference carried, while the ohm resistor 44 provides some isolation of the coaxial cable 76. The coaxial cable 76 is of a low capacitance in order to reduce losses at AM radio frequencies. I

It will therefore be appreciated that the use of the stub 90 in conjunction with the primary coaxial cable 76 produces an automatic switching permitting either AM or FM signals to be effectively transmitted from the antenna 10 to the receiver 20. At AM frequencies the stub 90 results in an open circuit to the radio receiver, while at FM frequencies the completed circuit to provide maximum reception of FM frequencies is produced.

Various modifications to the inventive concept may be apparent to those skilled in the art without departing from the scope of the invention.

I claim:

1. An antenna system for receiving television, AM and FM signals comprising, in combination, a dipole antenna receiving AM and FM signals and having first and second output conductors, a first coaxial cable having first and second ends and having a first inner conductor encased within and electrically insulated from a first electrical conducting tubular shield, said first inner conductor having said first end electrically connected to said first output conductor and said sec ond end connectible to an AM/FM radio receiver, a second coaxial cable having first and second ends and having a second inner conductor encased within and electrically insulated from a second electrical conducting tubular shield, said second inner conductor having said first end electrically connected to said second output conductor, said second coaxial cable being of such length as to terminate at approximately maxiumum FM signal magnitude, said first and second shields being electrically interconnected and disposed in close prox- 6 imity to each other in substantially parallel relation, said first ends of said cables being disposed adjacent each other, said first and second inner conductors being electrically insulated from each other and from said interconnected shields.

2. In an antenna system as in claim 1, first and second pairs of television signal lead conductors, each pair including a first conductor and a second conductor, said first and second conductors, respectively, of said leads being interconnected, said first conductor leads being connected to one of said output conductors and said second conductor leads being connected to the other of said output conductors, and signal isolation means interposed between said leads and the associated output conductor. 7

3. In an antenna system as in claim 1 wherein said second coaxial cable is of a length approximately one quarter of the wavelength of the FM signals to be received.

4. In an antenna system as in claim 3 wherein said second coaxial cable length is one quarter wavelength at approximately Mhz.

Claims (4)

1. An antenna system for receiving television, AM and FM signals comprising, in combination, a dipole antenna receiving AM and FM signals and having first and second output conductors, a first coaxial cable having first and second ends and having a first inner conductor encased within and electrically insulated from a first electrical conducting tubular shield, said first inner conductor having said first end electrically connected to said first output conductor and said second end connectible to an AM/FM radio receiver, a second coaxial cable having first and second ends and having a second inner conductor encased within and electrically insulated from a second electrical conducting tubular shield, said second inner conductor having said first end electrically connected to said second output conductor, said second coaxial cable being of such length as to terminate at approximately maxiumum FM signal magnitude, said first and second shields bEing electrically interconnected and disposed in close proximity to each other in substantially parallel relation, said first ends of said cables being disposed adjacent each other, said first and second inner conductors being electrically insulated from each other and from said interconnected shields.

2. In an antenna system as in claim 1, first and second pairs of television signal lead conductors, each pair including a first conductor and a second conductor, said first and second conductors, respectively, of said leads being interconnected, said first conductor leads being connected to one of said output conductors and said second conductor leads being connected to the other of said output conductors, and signal isolation means interposed between said leads and the associated output conductor.

3. In an antenna system as in claim 1 wherein said second coaxial cable is of a length approximately one quarter of the wavelength of the FM signals to be received.

4. In an antenna system as in claim 3 wherein said second coaxial cable length is one quarter wavelength at approximately 100 Mhz.

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