Receiving Antenna For Miniature Radio Receiver

Abstract

Receiving antenna for miniature radio receiver formed by conducting U-shaped member having substantially parallel elongated arms which form sides of the housing of the receiver and a connecting portion which forms one end of the housing. When the receiver is in the normal position for use, the arms are positioned vertically with the connecting portion at the top, and the U-shaped member acts as an inductive loop antenna to detect the H-field of the electro-magnetic wave. A reactance network, which is capacitive in the frequency range of interest, is connected to the open ends of the arms. The reactance network can be adjustable to tune the antenna for various frequencies, the antenna having been found suitable for use in the frequency range from 148 to 173 megacycles.

Parent Case Text

This application relates generally to antennas for miniature radio receivers, and more particularly to an antenna formed by part of the radio receiver housing. This application is a continuation-in-part of co-pending application Ser. No. 85,429, filed Oct. 30, 1970, now abandoned.

Description

BACKGROUND OF THE INVENTION

Miniature radio receivers are used in many applications such as for personal paging or for receiving broadcast transmissions for entertainment purposes. There is a problem in providing an antenna for such a receiver which does not increase the size of the receiver, and which provides effective signal pick-up of frequencies extending from the order of one magahertz up to frequencies of 500 megahertz or more. Ferrite rod antennas have been used, but these antennas take up substantial space and have the disadvantage that they are highly directional. This is objectionable for an antenna that is to be used with a receiver worn on the body, as the effectiveness of the antenna depends upon the position of the person wearing the same.

The provision of an antenna which is external to the receiver is also objectionable, particularly when the antenna is to be worn on the body of the user. Such an antenna increases the effective size of the receiver, and detracts from the appearance thereof. It has been proposed to use a part of the housing of the receiver for the antenna, but a satisfactory arrangement has not previously been provided, especially for use at frequencies under 200 megahertz.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an improved receiving antenna for a miniature radio receiver.

Another object of the invention is to provide an antenna for a radio receiver to be worn on the body of the user which provides effective signal pick-up and which has no projecting parts extending outside the receiver housing.

A further object of the invention is to provide an antenna for a miniature receiver which does not contribute substantially to the size of the receiver.

A still further object of the invention is to provide a receiving antenna for a miniature receiver wherein a part of the housing forms the wave receiving antenna member.

The antenna of the invention is formed by a flat metal cover formed into a U-shape and which also serves as two opposite sides and one end, or parts thereof, of the housing for a miniature receiver. In the normal position of the receiver, when worn on the body of the user, the two elongated arms extend vertically, with the connecting portion at the top. Connected to the open (bottom) ends of the arms is a reactance network which applies a capacitive reactance across the open ends of the cover so that the conducting cover forms an antenna which detects the H-field of the electro-magnetic wave to be received. Electrically, the antenna forms an inductive loop and the H-field is intercepted by the metal arms which form the loop. The reactance network is tunable to adjust the antenna for reception at a particular frequency, and has been used effectively in the frequency range between 148 and 174 megahertz. The signal pick-up of the antenna in free space is somewhat better at the front and at the back, than at the sides. When worn on the body, the pick-up becomes less directional. The cover may be removable to provide access to batteries within the housing, and also to permit removal of the receiver chassis therein for maintenance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a receiver having an antenna in accordance with the invention carried in the pocket of the shirt of the user;

FIG. 2 illustrates the receiver housing cover member which forms an antenna, and the connections thereto;

FIG. 3 is a schematic diagram showing the electrical circuit of the antenna; and

FIG. 4 is a schematic diagram of the antenna with a different reactance network coupled thereto.

DETAILED DESCRIPTION

In FIG. 1 there is shown a person carrying a paging receiver 10 with an antenna in accordance with the invention, with the receiver carried in the shirt pocket of the user. The receiver has a clip 12 on the front side for holding the receiver so it will not fall out of the pocket if the person stoops over or moves suddenly. The receiver has a housing including a part 14 which is molded of plastic material and forms the main support for the components for the receiver, and also a part of the walls of the housing. A cover 16 slides over the molded plastic member 14 and forms a large portion of the front, back and top walls of the housing. This cover is formed of a flat sheet of conductive metal which has been formed in the shape of a U having elongated arms 18 and 19 and a top connecting portion 20.

The cover 16 may be slid with respect to the plastic part 14 to provide access to batteries within the receiver housing. The cover may be completely removed from the plastic part to give access to the chassis of the receiver and/or to permit disassembly of the receiver, as to remove the chassis. The structure of the molded part 14 and the co-operation therewith of the cover 16 is described in co-pending application Ser. No. 65,453 of Thomas R. Hutchinson and Edward J. Caper, filed Aug. 20, 1970.

The cover portion 16 is shown disassembled from the receiver in FIG. 2. The conducting arms 18 and 19 which form the transmission line may have a length of about 4.3 inches and a width of about 1 inch. The connecting portion 20 is continuous with the arms and thus has a width of about one inch, and has a dimension between the two arms 18 and 19 of about 0.6 inch.

As shown in FIG. 2, the molded plastic member 14 has spring biased gold plated contacts 22 and 23 which engage the inside surfaces of the arms 18 and 19, at the ends thereof remote from the connecting portion 20. These spring biased contacts make good electrical contact with the arms of the conducting cover 16.

FIG. 3 illustrates the connections of the cover 16 to the receiver circuit. As previously stated, connection is made to the arm 18 of the cover by contact 22. This contact is connected to the reference ground of the receiver chassis. The other arm 19 is connected by contact 23 to a reactance circuit which includes inductor 25 and capacitors 26 and 27. The contact 23 is connected to an intermediate tap on the inductor 25. The inductor 25 may have a movable core to control the inductance thereof. The circuit including coil 25 and capacitors 26 and 27 is adjusted to be capacitive at the frequency of operation, so that the connections to the cover 16 in effect connects a capacitor across the open end thereof. The signal picked up by the antenna is derived from the reactance network at the common connection between capacitors 26 and 27, and may be coupled to the base electrode of transistor 30 which functions as a radio frequency amplifier. This is merely representative of various circuits for utilizing the received signal.

As shown in FIG. 3, the arm 18 of the conducting cover 16 at the back side of the receiver is connected to ground. When the receiver is carried in the pocket of the person using the same (FIG. 1), this grounded arm is adjacent the body of the person. The H-field of the electro-magnetic wave to which the antenna is subjected induces current in the inductive loop formed by the U-shaped conducting member 16. Although the structure shown has the connecting portion 20 between the arms 18 and 19 at the top, the antenna will operate just as effectively with the conducting portion which shorts the transmission line at the bottom.

FIG. 4 shows another embodiment of the reactance circuit which may be used with the antenna. The lower end of conducting arm 18 of the U-shaped conducting member 16 is connected to ground by spring contact 22. The end of conducting arm 19 is connected by contact 23 to a reactance circuit having a plurality of inductor parallel branches connected to ground. The first branch includes variable inductor 32 connected in series with capacitor 33. The inductor 32 can be adjusted for operation of the antenna at the desired frequency. Capacitor 33 is provided so that the inductor can be of a value to provide the required tuning range. The second branch includes capacitor 35 which is selected for the particular band of frequencies involved. A capacitor of one value can be used for the frequency range from 148 to 154 megahertz, a second value for the range from 154 to 160 megahertz, and so forth. The third branch includes a diode 36 which is conducting on extremely strong signals to protect the receiver circuit. The fourth branch includes capacitors 38 and 39 connected in series.

The signal across the parallel reactance circuit is coupled by capacitor 40 to radio frequency amplifier 42, which may include transistors or other semiconductor devices. The diode 36 prevents application of strong signals thereto which might damage the devices. The junction between capacitors 38 and 39 is connected through choke 44 to battery 45. The battery is connected through switch 48 to terminal 50 to energize the receiver circuit. Terminal 43 can be used to apply charging current to the battery, and also forms a 50 ohm input to the radio receiver, which can be used for testing purposes.

The antenna as described has been shown to operate satisfactorily over the frequency range from 148 to 174 megahertz, being tunable to the specific frequencies involved by adjustment of the inductor 25. The antenna has also been found to operate effectively at other frequencies above and below the range specified. The antenna of the invention has been found to have a response in free space which is somewhat greater for signals from the front and from the back. This directional action is less pronounced when the pager is worn on the body, and in such case the antenna has an effective response in all directions. This is desired in a paging receiver in order to receive signals when the person is facing in any direction.

Claims

We claim:

1. An antenna for a miniature radio receiver adapted to be carried on a person including in combination, a flat conductive member formed in a U-shaped configuration having first and second elongated substantially parallel arms and a portion connecting said arms, said arms having a length substantially greater than that of said connecting portion, said conductive member forming a part of the housing of the receiver with said arms extending substantially vertical in the normal position of the receiver, and reactance means coupled to the ends of said arms opposite to said connecting portion, said reactance means presenting a capacitive reactance across said conductive member.

2. The antenna of claim 1 wherein said U-shaped conductive member forms an inductive loop antenna.

3. The antenna of claim 2 wherein said reactance means is adjustable to select the value of said capacitive reactance to tune said conductive member for reception of the H-field of an electro-magnetic wave.

4. The antenna of claim 1 wherein said reactance means includes an inductor and a pair of series connected capacitors connected in parallel with said inductor, said inductor having end terminals and an intermediate terminal, with one end terminal and said intermediate terminal being connected to said arms of said conductive member, and an output conductor connected to the junction of said capacitors.

5. The antenna of claim 4 wherein said inductor is variable for tuning said reactance means, and said one end terminal connected to said arm of said conductive member is connected to the ground potential of the receiver.

6. The antenna of claim 1 wherein said reactance means includes a plurality of parallel branches connected between said ends of said arms, one of said branches including a capacitor and another branch including a variable inductor for tuning the antenna for reception of waves of a particular frequency.

7. The antenna of claim 6 wherein said reactance means includes a parallel branch having a diode rendered conductive in response to a received wave which exceeds a predetermined strength.

8. An antenna for a miniature radio receiver adapted to be carried on a person with one side thereof in proximity to the person, including in combination, a flat conducting member formed in a U-shaped configuration having first and second elongated substantially parallel conducting arms and a conducting portion connecting said arms, said member forming a part of the housing of the receiver with said arms constituting at least parts of the opposite sides and said conducting portion constituting at least part of the top of the housing, said arms of said U-shaped conducting member extending vertically in the normal position of the receiver with one of said arms in proximity to the person, and reactance means coupled to the ends of said arms opposite to said connecting portion for deriving signals therefrom.

9. The antenna of claim 8 including spring biased contact means engaging said arms at the ends thereof opposite to said conducting portion for making electrical connections between said arms and said reactance network.

10. The antenna of claim 9 wherein said contact means engaging said one arm is connected to ground potential of the receiver.

11. The antenna of claim 10 wherein said reactance means includes an inductor and a pair of series connected capacitors connected in parallel with said inductor, said inductor having an end terminal connected to said contact means connected to said arm forming part of said one side of the housing and an intermediate terminal connected to said arm forming part of the opposite side of the housing.

12. The antenna of claim 11 wherein said inductor is variable to control the tuning of said reactance means and is adjusted so that the reactance means presents a capacitive reactance across said ends of said arms.

13. The antenna of claim 10 wherein said reactance means includes a plurality of parallel branches connected between said ends of said arms, with one branch including a capacitor, a second branch including an adjustable inductor and a third branch including a pair of series connected capacitors.

14. The antenna of claim 13 wherein one of said parallel branches includes rectifier means selectively rendered conductive in response to a received wave above a predetermined strength.

15. The antenna of claim 8 wherein said reactance means is tuned so that said U-shaped conducting member forms a loop antenna for receiving the H-field of an electro-magnetic wave of a particular frequency.