US2767309A

US2767309A - Protective device for radio receivers

Info

Publication number: US2767309A
Application number: US409564A
Authority: US
Inventors: Frederick A Schaner
Original assignee: AIR ASSOCIATES Inc
Current assignee: AIR ASSOCIATES Inc
Priority date: 1954-02-11
Filing date: 1954-02-11
Publication date: 1956-10-16
Anticipated expiration: 1973-10-16

Description

ilnited States Patent PROTECTIVE DEVICE FOR RADIO RECEIVERS Frederick A. Schaner, Fair Lawn, N. J., assignor to Air Associates, Incorporated, Teterboro, N. J., a corporation of New Jersey Application February 11, 1954, Serial No. 409,564

Claims. (Cl. 250-20) This invention relates to protective devices for radio receivers which may be used in the same vicinity as high powered radio transmitting stations. The invention has particular reference to circuit elements which are used in radio receiving sets to prevent undue heating of input circuit components which receive radio waves from an antenna.

There are many cases where a sensitive receiving set is located close to a high powered transmitting antenna and even if the receiving set is not tuned to the high powered wave there still may be currents and voltages set up in the input portions of the circuit which may cause permanent damage. Such a condition exists aboard boats which use many forms of transmitting and receiving equipment, including radar, position locating systems, and other forms of high powered transmitting systems. Small portable radio receivers must necessarily use moderate size wire in the tuning coils which form part of the input circuit and when such equipment is subjected to the application of high power radio waves the coils may be damaged.

In order to protect the input circuits of such radio receivers a device must be used which will not materially reduce the radio signal of the desired frequency and yet must be able to divert or otherwise eliminate high powered undesired signals even when the set is not in operation.

One of the objects of this invention is to provide an improved protective device for radio receivers which avoids one or more of the disadvantages and limitations of prior art devices.

Another object of the invention is to provide a protective device which is ready for operation at any time whether the set is being used or not.

Another object of the invention is to provide a pro tective device which requires little space and which may be installed in receiving sets already manufactured.

Another object of the invention is to provide a protective device which requires no battery power for its operation.

The invention includes a low-pass filter current in combination with a sensitive relay having a single pole double throw set of switching contacts and a rectifier system which permits the relay to be operated by the radio frequency waves. This combination is inserted in the radio receiver between the antenna and the input circuit. When a high powered undesired signal is applied to the antenna the relay is operated and a resistor is connected to the filter circuit to absorb the undesired signal.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

Fig. 1 is a block diagram showing the relationship of the filter and relay in connection with the other receiver components.

Fig. 2 is a schematic diagram of connections showing the filter, relay and resistor connected to the input circuit of the radio receiver.

Fig. 3 is a schematic diagram of connections of an alternate system of connecting a rectifier element to the relay winding.

Fig. 4 is a schematic diagram of connections of another alternate method of connecting the relay winding and a rectifier system which employs both halves of the received power.

Fig. 5 is a schematic diagram of connections indicating a low-pass filter for ultra-high frequencies.

Referring now to Fig. 1 an antenna 10 may include the usual single conductor aerial and ground or it may comprise a more elaborate array of antennas and reflectors. A filter circuit 11 is connected to the antenna and is designed to eliminate all those frequencies above the frequencies used by the radio receiver. A relay circuit 12 is connected between the filter circuit and a radio receiver circuit 13. The output of the radio receiver may be connected to a transducer or a recording system (not shown).

The filter section 11 includes a series of inductors 14 and a series of parallel connected capacitors 15. Such a filter is well known in the art and has been employed for the elimination of undesired signals for many years. The relay 12 includes a winding 16 and an armature 17 on which is secured a movable contact 18.

Stationary contacts

20 and 21 are part of the relay system, contacts 20-48 comprising a normally closed combination and contacts 21-18 forming a normally open combination. A non-inductive resistor 22 is connected between contact 21 and the common ground connection 23. The input coil 24 which forms part of the input circuit of the radio receiver 13 is connected between the common conductor 23 and contact 20 and is thereby connected through the filter to the antenna 10. In order to derive a direct current component from the radio fr quency wave a rectifier element 25 is connected in series between the output of the filter circuit and the relay winding 16 and in order to further eliminate the alternating component of the radio frequency wave a capacitor 26 is connected across the terminals of the relay winding 16.

The operation of this circuit is as follows: when the radio receiver 13 is in operation receiving waves within its desired range and amplitude, the signals pass through the filter, through

contacts

18 and 20, to the input coil 24 and thence to the remainder of the radio receiver circuity. The desired signals are attenuated very slightly by the filter circuit and only a small amount of power is shunted through the rectifier 25 and the winding 16. The circuit constants are adjusted so that this loss is a very small amount and does not detract from the usefulness of the radio receiver. If now a very strong undesired signal should be applied to the antenna having a frequency greater than the cut-off frequency of the low-pass filter the filter circuit alone will cause its elimination and no high current surges will reach coil 24. If a very powerful transmitted signal from a nearby transmitting station is applied to antenna 10 within the range of the radio receiver or at a frequency which is less than the range, a few cycles will pass through

contacts

18 and 20 and the coil 24 but after a very short time interval the current through rectifier 25 and winding 16 will attract armature 17 transferring contact 13 from contact 20 to contact 21 thereby diverting the applied power from coil 24 to resistor 22. This resistor is made with suificient heat capacity to withstand any surge which may be received by the antenna. As soon as the undesired signal stops or is reduced to a value which will not harm the input circuit, contacts 18 are returned to their original position and the circuit is ready for receiving desired signals Within the frequency range of the receiving set. It should be noted that reversion to normal operation is accomplished without any manual operation or resetting device. It should also be noted that this circuit operates regardless of the setting of the remainder of the radio receiving 'set.

The circuit shown in 'Fig. 3 is the same as the relay circuit shown in Fig. 2 except that a rectifier element 28 is connected in parallel across the terminals of winding 16 and a resistor 27 is connected between armature 17 and the relay winding. This circuit works in the same manner as the circuit shown in Fig. 2. i

The circuit shown in Fig. 4 uses a split relay

winding comprising coils

16A and 16B, the center tap thereof being connected to armature 17 and the filter circuit. The outer terminals of winding 16 are connected together and to the grounded line 23. This alternate system provides a double-wave rectification but otherwise is similar to the circuit shown in Fig. 2.

The circuit in Fig. shows an ultra-high low-pass filter using capacitors connected in parallel and the self inductance of

conductors

32 and 33 as the inductance which combines with the capacitance of elements 15 to produce the filtering action. It will be obvious that the lengths of conductors between the junction points of capacitors 15 is of prime importance and must be carefully measured to produce the desired results.

A low frequency filter of the type shown in Fig. 2 may be used to stop frequencies within the range of fifty to six hundred megacycles while a filter such as that shown in Fig. 5 may be employed to eliminate frequencies within the range of 450 to 3500 megacycles.

While there have been described and illustrated specific embodiments of the invention, it will be obvious that various changes and modifications may be made therein without departing from the field of the invention which should be limited only by the scope of the appended claims.

What is claimed is:

1. A protective device for radio receivers comprising, a pair of contacts in series connection between an antenna and an input circuit of the radio receiver, a relay having a winding coupled by a common conductor to the radio receiver and one of said contacts, a relay armature carrying the contact which is coupled to the input circuit, and a resistor connected between the common conductor and a third relay contact which is connected to the armature contact when the relay is operated.

2. A protective device for radio receivers comprising, a filter circuit and a pair of contacts in series connection between an antenna and an input circuit of the radio receiver, a relay having a winding connected between the conductor to the radio receiver and one of said contacts, a relay armature carrying the contact which is coupled to the filter circuit, and a resistor connected between said common conductor and a third relay contact which is connected to the armature contact when the relay is operated.

3. A protective device for radio receivers comprising, a filter circuit and a pair of contacts in series connection between an antenna and an input circuit of the radio receiver, a relay having a winding connected between a common conductor to the radio receiver and one of said contacts, a relay armature carrying the contact which is coupled to the filter circuit, and a resistor connected between said common conductor and a third relay contact whereby the relay is operated and the input circuit switched to the resistor whenever a predetermined amount of received energy is collected by the antenna.

4. A protective device for radio receivers comprising, a filter circuit and a pair of contacts in series connection between an antenna and an input circuit of the radio receiver, said filter circuit adjusted to eliminate received radio waves having frequencies which lie beyond the range of said receiver, a relay having a winding connected between a common conductor to the radio receiver and one of said contacts, a relay armature carrying the contact which is coupled to the filter circuit, and a resistor connected between said common conductor and a third relay contact which is connected to the armature contact when the relay is operated.

5. A protective device for radio receivers comprising, a filter circuit and a pair of contacts in series connection between an antenna and an input circuit of the radio receiver, said filter circuit adjusted to eliminate received radio waves having frequencies which lie beyond the range of said receiver, a relay having a winding whic receives current from the filter circuit, a rectifier connected in series with the relay winding for producing a direct current component therein, an armature on said relay which breaks the connection between said contacts when the relay is operated, and a resistor which is connected across the filter circuit whenever the relay is operated.

6. A protective device for radio receivers comprising, a filter circuit and a pair of normally closed contacts in series connection between an antenna and an input circuit of the radio receiver, said filter circuit adjusted to eliminate received radio waves having frequencies which lie above the range of said receiver, a relay having an operating winding which receives current from the filter circuit, a rectifier connected to said winding so that a direct current component is produced therein whenever radio frequency power is applied to the winding, an armature operated by said winding current which opens said normally closed contacts, and a resistor which is connected across the filter circuit and a common grounded conductor whenever the relay is operated.

7. A protective device for radio receivers comprising, a filter circuit and a pair of normally closed contacts series connection between an antenna and an input circuit of the radio receiver, said filter circuit adjusted to eliminate received radio waves having frequencies which lie above the range of said receiver, a relay having an operating winding which is coupled to the filter circuit through a rectifier circuit, said winding receiving direct current whenever radio frequency power is delivered by the filter, an armature operated by said winding current which opens the normally closed contacts, and a resistor which is connected across the filter circuit whenever the relay is operated.

8. A protective device for radio receivers comprising, a filter circuit connected between a receiver antenna and the input to the receiver, said filter adjusted to eliminate received radio waves having frequencies which lie beyond the range of said receiver, a relay having an operating winding, an armature, and a single pole double throw system of contacts, one pair of which is normally closed, said normally closed contacts connected in series between the filter and the input to the receiver, said operating winding connected across the output of the filter circuit, and a resistor which is connected between part of the filter circuit and a normally open contact on the relay.

9. A protective device for radio receivers comprising, a filter circuit connected between a receiver antenna and the input to the receiver, said filter adjusted to eliminate received radio waves having frequencies which lie beyond the range of the receiver, a relay having an operating winding, an armature, and a single pole double throw system of contacts, one pair of which is normally closed, said normally closed contacts connected in series between the filter and the input to the receiver, said operating winding coupled to the output of the filter circuit through a rectifier so that a direct current is applied to the operating winding whenever the filter circuit transmits a radio wave, and a resistor which is connected between part of the filter circuit and a normally open contact on the relay.

it). A protective device for radio receivers comprising, a filter circuit connected between a receiver antenna and the input to the receiver, said filter adjusted to eliminate winding, an armature, and a single pole double throw References Cited in the file of this patent system of contacts, one pair of which is normally closed, UNITED STATES PATENTS said normally closed contacts connected in series between the filter and the input to the receiver, said operating Wheeler July 1932 winding coupled to the output of the filter circuit through 5 118 0398 Bmwn 1932 a rectifier so that a direct current is applied to the operat- 681460 July 1934 ing winding whenever the filter circuit transmits a radio 2,144,836 Dletnch 24) 1939 wave, a resistor which is connected between part of the 2,296,101 Foster Sept 15, 1942 filter circuit and a normally open contact on the relay, said relay adjusted for operation when the filter circuit 10 delivers an amount of radio frequency power which is sufficient to damage the radio receiver.