US2289147A - High frequency receiver - Google Patents

Description

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Patented July 7, 1942 HIGH FREQUENCY RECEIVER Richard F. Shea, Bridgeport, Conn., assignor to General Electric Company, a corporation of New York Application August 22, 1940, Serial No. 353,665

(Cl. Z50- 20) 9 Claims.

My invention relates to high frequency receivers and more particularly to receivers adapted, for example, to home radio reception employing both unicontrolled tuning means variable over a desired range, and xed tuning means to tune the receiver to fixed frequencies in said range, the fixed frequencies being selected by switches, such as the push buttons of ordinary. household receivers. 2

It has for one of its objects to effect certain economies in the construction of such receivers.

A further object of my invention is to provide means to avoid employment of fixed tuning means in the interstage circuits operating at the received frequency.

A further object of my invention s to provide means whereby when the receiver is adjusted for push button operation, the interstage tuned circuits are rendered ineiective, or removed from the circuit, and an untuned broad band pass network is utilized to furnish the desired interstage coupling.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single gure represents an embodiment of my invention.

Referring to the drawing I have illustrated therein a portion of a radio receiver comprising a radio frequency amplier employing an electron discharge device I, a local oscillator 2, and a converter 3 for converting the received oscillations and the oscillations produced by the local oscillator 2 to oscillations of xed frequencygor all received frequencies. The output of this converter, which is of constant frequency for all received frequencies, is supplied to a tuned circuit 4 tuned to this constant frequency which in a superheterodyne receiver is ordinarily known as the intermediate frequency. Those portions of the receiver subsequent to the circuit 4 are not shown in the drawing since their nature does not pertain to my present invention.

The control grid of the radio frequency amplifier I is connected through a coupling condenser 5, the movable contact 'I of a `switch. designated on the drawing as S, and a tuning condenser 8, to the cathode of the discharge device. Similarly, the control grid 9 of the converter 3 is connected through movable contact I0 of the switch S and tuning condenser I I to the cathode of the discharge device 3. Likewise, the control grid I2 of the local oscillator is connected through the grid condenser I3 thereof, movable contact I4 of the switch S and tuning condenser I 5 to the cathode of the discharge device 2. The tuning condensers 8. II, I5 are arranged for unicontrolas indicated by the dotted lines shown on the drawing interconnecting these different condensers, and comprise the ordinary means for tuning respectively the input circuit of the amplier, the coupling circuit between the amplier and the converter, and the local oscillator thereby to select the desired stations which are to be received.

The switch S is the band change switch of the receiver and may be of the ordinary Yaxley wafer construction but for purposes of illustration is shown on the drawing as having a plurality of contacts such as the contacts Ii, 1, Ill, I4 already mentioned and others presently to be mentioned, all interconnected for unicontrol as indicated by the dotted lines to which the character S has been applied on the drawing.

This switch has four positions. In the position shown it connects the receiver for tuning by means of the unicontrolled variable ciondensers 8, II, I5 over a range of frequencies which may be the broadcast band. This may be designated the B position of the switch. It may be moved to the left to either of two positions C and D in which it connects the receiver for tuning over either of two higher frequency bands by means of condenser 8, II, I5, or it may be tuned to the right to position A in which it disconnects condensers 8, II, I5 from the circuit of the receiver and substitutes in the place of condenser 8 a fixed condenser I'I plus the push button switching mechanism I8 shown at the top of the drawing. It also substitutes for condenser I5 the xed condenser I 5' shunted by an inductance I9 connected thereto through certain switches of the push button mechanism I8.

It also, in its A position, disconnects condenser I I from the receiver circuit so that the inductive coupling circuit between amplier I and converter 3 is untuned and rendered ineiective, and at the same time it disconnects a xed by-pass condenser 20 from the receiver thereby to render effective between the amplifier I and the converter 3 a broad band resistance capacity coupling comprising elements 26, 30, 56 and 58, which will be more particularly mentioned hereinafter.

The circuits of the receiver in each position of the switch S will now be described in detail. With the switch in the position B, which is that shown on the drawing, the input circuit to the amplifier I extends through the condenser 5, variable contact 5 of the switch S in its B position and loop antenna 2l to ground 22 and thence back to the cathode of ampliner I. The loop antenna 2| is designed for operation in the broadcast band which extends from about 550 to 1700 kilocycles and is,tuned by the variable condenser 8 and the trimmer condenser 23.

The anode circuit of the amplifier extends through the primary winding 24 of a transformer 25 and through resistance 2i to the source of high voltage operating potential for the receiver, the positive terminal of which is indicated by the line 21, and the negative terminal of which may be grounded. With the switch S in the position shown the secondary winding 28 of this transformer is connected by means of contacts 29 and I0 thereof across the variable condenser II, these movable contacts 29, I3 being connected to the control grid of the converter 3. This control grid is connected through the winding 2B and a resistance 30 to the bus 3i which may be the automatic volume control bus of the receive This bus includes a resistance 32 and is connected to ground through a condenser 33 which elements may comprise an ordinary automatic volume control filter circuit. The secondary winding 28 of transformer 25 is tuned by means of condenser II and trimmer condenser 34.

At the same time the cathode of the local oscillator 2 is connected through movable contact 35 of the switch S to an intermediate point on the tuned circuit 35, one terminal of which is connected to ground and thence through condenser 31 to the anode of the discharge device 2, and the opposite terminal of which is connected through a series alignment condenser 38, movable contact 39 of the switch, and grid condenser I3 to the grid of the oscillator 2. This grid is connected to ground through the ordinary oscillator grid resistance 40. The tuned circuit 36 is tuned over the -band of frequencies corresponding to the broadcast band of received frequencies by means of the condenser I5.

With the circuits as thus described the receiver is adapted for reception of the broadcast band of frequencies by means of the loop 2| and by variation of the tuning of the receiver by means oi' condensers 8, II; I5.

The loop antenna 2| is provided with a tap connection 4I which is connected through an inductance 42 and contact 43 of the switch to an antenna 44 which may be the ordinary outdoor antenna for home reception which may be utilized in situations where the directvity of the loop 2| is not highly important.

Such a connection of an ordinary outdoor antenna and loop is shown and claimed in application Serial No. 238,417, led November 2, 1938 by George W. Fyler entitled Radio receivers, now Patent No. 2,222,709, issued November 26, 1940, and which is assigned to the assignee of my present application. The antenna is connected to ground through a resistance 45 which coacts with the inductance 42 to aid in the suppression of image frequencies.

If the switch be moved to its C position, the input to the amplifier I is changed by substitution of loop 43 for loop 2|, this loop being tuned by the condenser l and trimmer 41 for reception of a higher band of frequencies. An inter- II and trimmer 53' over said higher frequency mediate point on the loop 48 is also connected through contact 43 of the switch to the antenna 44, but in this case no .means for suppressing image frequencies is employed.

A second primary winding 41 of the interstage coupling transformer 25 is now connected in parallel with the primary winding 24 'by means of contact 48 of the switch and secondary winding 28 is now removed from the grid circuit of the converter and in its place is substituted secondary winding 49, this winding being tuned by condenser I I' and trimmer 49.

The oscillator circuit is now changed by contact 39 of the switch by substitution of oscillating circuit 50 for the oscillating circuit 38.

If switch S be moved to its D position, loop 5I is substituted in place of loop 46, this loop being tuned by means of condenser 8 and trimmer 52 over a still higher band of frequencies. Primary winding 41 is now removed from the output circuit of the discharge device II leaving only primary winding 24. Secondary winding 53 is now inserted by means of contact 29 of the switch in the grid circuit of the converter, this secondary winding being tuned by condenser band. In the oscillator circuit the tuned circuit 54 is substituted for the tuned circuit 50.

In all positions B, C and D of switch S the coupling between the radio amplifier I and converter 3 is effected practically entirely by the transformer 25 and condenser 58. Resistance 25 may desirably be of about twenty-two hundred ohms and has connected in parallel with it the series combination of coupling condenser 56 and by-pass condensers 2U and 2li' and hence it has very small effect upon coupling between the circuits of the two discharge devices. Resistance Y30 is shunted by the path comprising condenser 20 connected between its upper terminal and ground and condenser 33 connected between its lower terminal and ground, and thus has practially no eifect on the coupling between the circuits. Condenser 55 is of about two or three hundred micro-microfarads.

Ii.' the switch S be moved to the right, to the A position, the tuning condensers 8, I.I, I5 are all removed from the circuit and the broadcast band loop 2i is restored to the circuit. The grid circuit of the ampliiier I is now tuned by means of a condenser I1 which is connected thereto through the various contacts of the push button assembly I8. Similarly, the tuned circuit 38 of the oscillator is now restored to its circuit relation with discharge device 2 and has connected across it the inductance I9. This circuit extends from ground through the circuit 3B, movable contact 39 of switch S, movable contact I4 of switch S, conductor 51, upper contacts of the lower armatures of push button assembly I8 and inductance I9 to ground, this circuit being tuned to a desired frequency by adjustment of inductance I9. Condenser I'I is removed from circuit by contact III, and therefore, the transformer 25 is no longer tuned thereby. The by-pass condenser 20 is open crcuted by contact 55 o1' the switch. In this way the transformer is rendered substantially ineffective as a coupling means between the amplier and converter but resistances 26 and 30 are now effective as coupling resistors in a coupling network comprising these resistors and condensers 56 and 58, the latter of which is connected directly between the anode of ampliner I and the control grid of the converter. Theseelements 26, 30, 5E and 58 may be proportioned to act as a wide band coupling network which is effective to transmit any frequency in the broadcast band or which may be selected by the push button assembly.

The various stations which may now be selected are determined by the push buttons 60, 6|, 62, 63, 64, 65 on the push button assembly. Push buttons 6U to 64 are each provided with two movable contacts or armatures, one of which is connected in the amplifier input circuit and the other in the oscillator circuit, and each armature has two positions, namely, the position shown in the drawing and a lower position in which it is retained by means of a latch member 6B having slots 61 therein through which the push button members extend. The latch 66 is biased by means of a spring 68 against the push button. Each push button member is also provided with a pawl 69 which cooperates with the slot 61 on the latch so that whenthe push button is operated `downwardly the latch is moved to the right until the pawl has completely passed the latch. The latch then returns to its initial position latching the operated push button in its lower position. When the latch is thus operated, any other push button previously operated to its lower position, is released. Push button 65 is not :provided with any contact armatures but operates when pressed to restore buttons 60 to 64 to the position shown in the drawing inserting -condenser I1 and coil |9 in their respective circuits.

It will be understood that the mechanical details of this push button assembly just described are described solely by Way of illustrating one form of push button assembly which may be used. Any of the forms now commonly in use may be employed.

When push button 60 is operated to its downward position, the input circuit of the receiver is tuned to a frequency determined by fixed condenser and the local oscillator is tuned to a frequency determined by inductance 1|. When push button 6| is operated, push button 6G is released and the input of the receiver is then tuned to a station determined by condenser 12 and the local oscillator is tuned to a frequency determined by inductance 13. The condensers I1, 10, 12, etc., may, if desired, be of any suitable type variable for purposes of initial adjustment and the inductances I9, 1|, 13, etc., may be of the iron core type in which the core is variable for variation of the tuning of the oscillator over a desired range for purposes of initial adjustment.

It will be seen that by the use of my invention i it is unnecessary to provide on the switch assembly I8 an additional set of movable contacts and associated tuning reactances controlled by the push buttons to effect the tuning of the interstage coupling circuit between amplifier and converter 3, this complication being avoided by the simple use of the resistance capacity coupling circuit 26, 30, 56, 58, which is rendered effective by means of conta-ct 55 of the switch. Thus, when the receiver is adjusted for push button tuning, Wide band coupling is used in the interstage circuits and tuning thereof to the different stations preset by the push button assembly is avoided.

In addition, with switch S adjusted to either the B or C positions resistance and condenser 20 serve as an additional filter in the automatic volume control circuit to the grid 9 of the converter. It aids in reducing audio frequency or intermediate frequency, feed back from the automatic volume control rectifier, now commonly employed in suchv receivers,'through conductor 3| now resistance 30 to the grid 9 of the converter. When switch S is in the D position, for operation in the highest frequency band the lower terminal of resistance 30 is grounded and the automatic volume control circuit to grid 9 of the converter is interrupted by contact of the switch. This is desirable because in the upper portion of the D frequency band voltage of the frequency of the oscillator appears in considerable quantity on the grid 9 producing rectication and unidirectional voltage on the filter resistors in the automatic volume control circuit which tends to bias the amplifier and converter to cut off. This is avoided by interrupting the circuit at the contact 80.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto since many modifications both in the circuit arrangement and in the instrumentalities employed may be made and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a pair of electron discharge amplifiers, coupling means between said amplifiers tunable over a range of frequencim, untuned means coupling said amplifiers over the same range of frequencies, and switching means for rendering said tunable coupling means and said untuned coupling means alternatively effective over said range of frequencies.

2. In combination, a pair of electron discharge amplifiers, one of said amplifiers having an outputcirouit, and the other of said amplifiers having an input circuit, a coupling between said circuits, a resistance in said output circuit, means to tune said coupling to a desired frequency, means to render said tuning means ineffective and means to supply potential variations on said resistance to said input circuit at all frequencies over a Wide range.

3. In combination, a pair of electron discharge amplifiers, tunable coupling means between the output electrodes of one of said amplifiers and the input electrodes of the other amplifier, a circuit between said output electrodes including an element of said coupling means and a resistance, a shunt path around said resistance, means connected to said coupling means to tune said coupling means to any desired frequency in a wide band of frequencies, means to render said last means ineffective and to interrupt said shunt path, and means to supply the potential variations on said resistance to said input electrodes.

4. In combination, a pair of electron discharge amplifiers, coupling means between said amplifiers, means to supply operating potential to the anode of one of said amplifiers through a resistance and an element of said coupling means, means to supply bias potential to a grid of the other of said amplifiers through a resistance and an element of said coupling means,a shunt path between the cathodes of said discharge devices and the points between said resistances and said reactive coupling means for currents of the frequency at which said amplifier operates a capacitance between said anode and grid, means to tune said coupling means to said frequency,

means to disable said tuning means and simultaneously to interrupt said shunt path, said resistances and said capacitance being proportioned to operate as a resistance capacity coupling network between said amplifiers over a wide range of frequencies. q

5. In combination, an electron discharge device having an anode circuit including the primary winding of a transformer and a resistance in series, a second electron discharge device having a grid circuit including a secondary winding of said transformer and a resistance in series, av

capacitance between the anode of said first electron discharge device and the grid of said second electron discharge device, a low impedance path between the cathodes of said discharge devices and the points on said circuits between said windings and the respective resistances for frequencies at which said discharge devices operate, and means to interrupt said path, said resistances and said capacity being proportioned to act as a resistance-capacity coupling between said discharge devices when said path is interrupted.

6. In combination, an electron discharge device having an anode circuit including the primary winding of a transformer and a resistance in series, a second electron discharge device having a grid circuit including a secondary winding of said transformer and a resistance in series, a capacitance between the anode of said first electron discharge device and the grid of said I,

second electron discharge device, a low impedance path between the cathodes of said discharge devices and the points on said circuits between said windings and the respective resistances for frequencies at which said discharge devices operate, a tuning reactance connected to said transformer to tune it to the frequency at which said discharge devices operate, and means to discon` means alternatively operative, the combination of a tuned coupling network between two stages in said receiver, said first tuning means including means to tune said coupling network to select any frequency in said range, a normally ineffective broad band coupling network between said stages, and means responsive to operation of said switching means to render said fixed frequency tuning means eective, to render said tuned coupling network ineffective and to render said broad band coupling network effective.

8. The combination, in a radio receiver having a tunable coupling network between different electron discharge stages of said receiver, of means to tune said receiver over a band of frequencies, said means including means to tune said network over said band of frequencies, switching means arranged to tune said receiver to any one of a plurality of fixed frequencies in said band, means to render said tuning means and switching means alternatively effective, a capacitive interstage coupling network, and means responsive to operation of said last means to render said switching means effective, to render said tunable coupling network ineffective and to render said capacitive coupling network effective between said stages.

9. In a high frequency receiver having a received frequency amplifier, a local heterodyne oscillator, and a converter to combine the received oscillations amplified by said amplifier with the oscillations produced by said local oscillator to produce additional oscillations, a tuned coupling between said amplifier and converter, said amplifier, tuned coupling and local oscillator being tunable over respective ranges of frequencies such that said additional oscillations are of constant frequency for all received frequencies, the combination of an untuned coupling between said amplifier and converter, switching means to tune said amplifier and oscillator to any one of a plurality of fixed frequencies throughout their respective ranges, and means responsive to operation of said last means to render said tuned coupling ineffective and said untuned coupling effective between said amplifier and converter.

RICHARD F. SHEA.

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