US1883794A

US1883794A - Radio receiving apparatus

Info

Publication number: US1883794A
Application number: US549164A
Authority: US
Inventors: Johnson John Kelly
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1931-07-07
Filing date: 1931-07-07
Publication date: 1932-10-18
Anticipated expiration: 1949-10-18
Also published as: NL36084C; GB384544A; FR739762A; DE684956C

Description

(m18, 19:42.y QJ. K @HNSQN 1,883,194

RADIO vRECEIVING' AIPPARATUS Filed' July '7. 1951 ATTORN EYS Patented kst. 18, 1,932 l UNITED STATES PATsNiT.- ori-ica JOHN KELLY JOHNSON, OF BYE, NEW YORK, .ASSIGNOB TO mm CORPORATION v RADIO BECEIVING'APPAMTUS Application mea July 7, iezn.V serial no.

The present invention relates to a radio frequency tuning system for use in connection with radio receivingapparatus bf the superheterodyne type. l

A problem common apparatus is the/selection of the desired signal and the rejection of undesired signals. A superheterodyne radio receiver is articularly sensitive to not only the desire signal but to a second frequency known as the image'frequency which is that frequency displaced above the local oscillator frequency by the same amount that the desired frequency is displaced below the local oscillator frequency. If the radio frequency tuning circuits of a superheterodyne respond tothe comparative close inxage7 frequenc and ifk a second transmittingstation is within the range of the receiver and operates at, afrequency at or near the image frequency, the local oscillator frequency currents will combine therewith and the intermediate frequency stages will pass the beat frequency thus produced, resulting in a signal which may be characterized as an unpleasant combination of the desired and undesired signals.

lt is the object of the present invention to prevent the response of radio .receivers to undesired signals and particularly the production of undesired image frequency signals in a superheterodyne receiver.

Various means have been proposed to eliminate the image frequency response occurring in superheterodynes. One such system utilizes a tapped secondary in the input transformer, the input to the first radio uency amplifier tubes being taken across a portion of the secondary transformer. The portion of the secondary above the tap, in conjunction with the tuning condenser, constitutes a radio frequency bv-pass circuit responsive to the undesired signal. Such a circuit is shown. for instance, in MacDonald Patent No. 1,680,424.

to all radio receiving tion, an input transformer is provided, and

the secondary is tapped at a point such that the portion of said secondary above the tap,

together with the tuning condenser, will constitute a radio frequency by-pass to signals of the image frequency and the terminals of the portion of the secondary below the tap of the undesired or image frequency.

As the entire secondary circuit is tuned to the desired frequency, the by-pass circuit, which includes the tuning element, is likewise tuned to the undesired or image frequency.

`The misalignment between the actual image frequency and by-pass frequency is made as slight as possible and may be made zero for any point of the range desired. The voltage variations vbetween the tap and the ground end'of the secondary are used to supply a voltage to a second tuned circuit, which circuit is vutilized to impress the signals upon the radio frequency amplifying devices, detectors, etc.

Having thus briefly described the invention, attention is invited to the accompanying drawing, in which Fig. 1 shows the imput radio frequency circuits o'f a radio receiver embodying this invention;

Fig. 2 shows the tuned radio frequency circuits, embodying this invention, used in con- `*will be at node potential relative tocurrents nection with the input of a radio receiver as, for instance, a superheterodyne; 1

Fig. 3 is an elementary circuit diagram illustratingy the principles of the present 1n- 5 vention; and

Figs. 4, 5, 6 and 7 are elementary diagrams of modified circuits for carrying out the principles of the invention.

Fig. 1 shows the tuned input of a radio relo ceiver. ln this figure the antenna A is connected to the ground G through the primary P of the transformer T1. The secondary S of the transformer is tapped at point 14, said tap being connected to the primary P2 of the transformer T2. 1n shunt with the secondary S is the tuning condenser C1, said secondary S and condenser C1 forming a tuned circuit 10 resonant to the frequency of the desired signals. Circuit 10 is made resonant to the desired frequency either by variation -of the condenser C1,made variable-as shown, or by variation of the inductance of the secondary S. The secondary S2 of the transformer T2 is shunted by condenser C2, forming the tuned circuit 12 which is tuned to the desired. frequency in a manner similar to that inwhich circuit 10 is tuned.

Condensers C1 and' C2 may be connected for uni-control operation, as indicated by the dotted line in Fig. 1, and the same control may be made to tune the remaining tuned circuits of the receiver. A

Circuit 12 is connected to the input of thermionic device 13 which may be the radio frequency amplifier or detector of a radio receiver, as desired.

Attention is now invited to Fig. 2 in which similar parts are indicated by the same reference figures. This circuit is particularly adapted for'use in a superheterodyne radio receiver. It differs from Fig. 1, just described, principally by the use of a volumecontrol variable resister R, a variable portion of lwhich is shunted across the primary P of the transformer T1. The cathode of the thermionic device 13 is also variably connected to ground thro gh the resistor R for the purpose of varying t e amplification of said device by varying its grid bias potential. Transformer '1 1 includes also a second primary P1 which may be wound on the secondary for the purpose of increasing the gain of said trans- I ormer by increasing the capacity coupling i between the primary and secondary. This circuit is in other particulars essentially the same as that shown in Fig. 1.

In view of the fact that the primary P2 of transformer T2 is inv shunt with a substantial portion of the tuning inductance S of transformer T1 of Fig. 1 and T1 of Fig. 2, it is desirable that its inductance be high in order to prevent its acting to short-circuit the portion of coil S below the tap, and thus interfere with the alignment of circuit 10 with the circuit 12.

As an example of what constants may be used for the various parts of the circuit constituting the invention, the following characteristics are given, although it is to be noted that others may be found satisfactory. How- P1-20 turns of #38 U. S. gauge double silk covered copper wire;

C1 and C2--O-350 micro-micro-farads. The secondary S comprises 125 turns and the tap is vtaken 51 turns from the ground end.

These characteristics are for a superhetero- 1 dyne receiver using an intermediate frequency of 175 kilocycles in which the image frequency is 350 kilocycles above the desired frequency.

The condensers C1 vandCz may be connected together for uni-control operation. The circuit of Fig. 3 is the same as the circuit shown in Fig. 1 except that the inductances are differently arranged for the purpose of explaining the action of the circuit used in accomplishing the objects of this invention. As previously described, the secondary S of transformer T1 is ta ped at point 14. The two portions Sfand S9' that, relative to the

points

14 and 15, S and C1 will constitute a-"by-pass to currents of an undesired frequency. It can, therefore, be seen that the voltage gain characteristic curve of the portion S will show zero voltage at the image frequency, whereas the natural resonance of the circuit 10 may be such that a considerable voltage will be developed at a frequency the same amount on the other side of the signal frequency, thus producing a non-symmetrical curve relative to the voltages between

points

14 and 15 at the different frequencies. may be so chosen that the misalignment between the by-pass frequency as varied when the condenser C1 is varied in tuning circuit 11 and the image frequency will be zero at any selected point in the range. Then the

points

14 and 15 will remain at substantially less potential difference relative to currents of such undesired frequency throughout the tuning range of the receiver.` The

points

14 and 15 are connected to the primary P2 of the transformer T2, thus forming a link circuit 11. It is to be noted that the primary P2 does not have impressed across it all of the voltage variations which are available across the secondary winding S, but only those existing across the substantially reduced portion S. However, the primary P2 is inductively related to the secondtuned circuit are so proportioned The tap point 14 12 through the secondary S2, the resonance characteristics of which permit the amplification to be made the maximum obtainable in the second of two coupled tuned circuits. In other words, substantially optimum coupling will be obtained regardless of the loss occasioned by the tapping of the secondary. Fig. 4 shows a coupling circuit in which the link circuit 11 includes a condenser C3. The o circuit 11 may be made resonant to a frequency below the band it is desired to receive, in order to increase the response of thewhole coupling circuit at low frequencies. For this purpose the inductance of P2 must be l5 `made relativel high, and the coupling between P2 and g2 must be relatively loose.

Fig. 5 is a second modification of the circuit constituting the present invention. In this circuit the link circuit 11" includes a portion S2 of the inductance S2 in addition to the series condenser C3. A circuit of this type gives a bettery response at high frequencies in which the current flowing in the linl circuit is greater. However, it is imff portant in this circuit that the capacity of C2 be small to prevent short-circuiting of the portion S of secondary S.

Fig. 6 shows a third modification of the circuits embodying the invention. In this cirsu cuit the primary P2 of the transformer T2 is closely coupled to the high-potential end of the resonant circuit 12. The winding P2 may be in such a direction relative to the winding of the secondary S2 that th inherent capacity coupling C.2 between the primary P2 and secondary S2 will either oppose orl aid the mutual inductivecoupling between said primary and secondary. In the event that the capacitive, coupling C4 is in opposition to the inductive coupling, the response of the circuits is reduced at the higher frequencies. Fig. 7 is still another modification of the circuits embodying this invention. In this circuit P2 is connected to the tapped secondsary S of transformer T1 and the other end of the primary P2 is` left unconnected. In this circuit the link circuit 11", comprises the portion S of transformer T2, the inherent capacity C2 between theprimary P2 and secondary S2 of transformer T2 and the leads connecting S with P2', and circuit. 12 with circuit 10. This circuit gives better response characteristics to the entire coupling circuit at the higher frequencies. The operation of circuits shown in Figs. 4,

5, 6 and 7 is similar to the operation of circuits shown in Figs. 1, 2 and 3 and may be summarized as follows: The tapped secondary S of the transformer T1 permits a bypassing in each instancefor theI undesired frequency as, for instance, the image fre quency in a superheterodyne. The voltage exlistng across the portion S of said secondary. is applied by means of a link circuit to 5,5 excite a second tuned circuit 12. Various means have been shown for coupling the

circuits

10 and 12, but it is to be understoodthat they are each based upon the same principles, although the method of obtaining the desired mutual coupling may be varied in accordance with the circumstances, as shown dfor the purpose of illustration in the various figures.

When the circuits constituting this invention are being used in a superheterodyne -receiver, the tap 14 is so chosen that the image frequency response of the tuning circuits will be reduced. However, when a tuned radio frequency receiver is used the tap may be so taken that any objectionable signal may be rejected. I claim: i fr 1. Signal selecting circuits for a radio receiver comprising a circuit :tunable to the frequency of the current it is desired to receive, a second circuit tunable to the same frequency, and a link circuit connecting portions of the impedances of each of said circuits, tlie portion of the impedance of the first of said circuits being shunted by a circuit resonant to the currentof a frequency it is not desired to receive and said link circuit being nade resonant to current of a frequency lower than the band of frequencies to which v said circuits are tunable.

2. A signal selecting device for a superheterodyne radio receiver which comprises a circuit ltunable to a current of the frequency it isV desired to receive, a second circuit likewise tunable to the current of the frequency it is desired to receive, and a link circuit connecting a portion of the impedance of said first mentioned circuit and inductively related to the second mentioned circuit, the portion of the impedance of said first mentioned circuit being so chosen that its terminals remain at substantially n ode potential relative to the image frequency of said receiver as the circuits are tuned, said circuits being so proportioned that the gain of said second circuit will compensate to some extent for the loss occasioned by the tapping of only a portion of the desired signal voltage across the first mentioned circuit.

3. A tuned radio frequency selective device for a radio receiver including a circuit tunable to the frequency -of a current to be received, asecond circuit also tunable to the frequency of the current to be received. and a link circuit connecting portions of the impedances of each of said circuits, the portion of the impedance of the first of said circuits being so selected that its terminals are at node potential relative to currents of an undesired frequency, and said link circuit having a resonance at a frequency outside the band of frequencies to be-,covered by said circuits whereby to emphasize the response to frequencies toward one side of the band.

f1. Signal selecting circuits for a radio re- Y ceiver which comprise al first circuit includsired to receive, a link circuit connected between said circuits including a portion of the inductance of the first of said circuits and at least a portion of the impedance of said second-mentioned circuit, said link circuit being proportioned so that the impedance shunting4 the selected portion of said inductance remains substantially resonant to current of a particular undesired frequency as the circuits are tuned, said link circuit being resonant to a frequency below the band of frequencies to which it is desired to tune the said circuits whereby the gain of said circuits is increased at low frequencies.

5. A signal selecting device for a super' heterodyne radio receiver which comprises a circuit tunable to a current of the frequency it is desired to receive, including aninductance and a capacity, a second circuit likewise tunable to the frequency`` of the current it is desired to receive, also including an inductance and a capacity, a link circuit connected toV a portion of the inductance of the said first mentioned circuit and inductively related to said second mentioned circuit, a portion of the inductance of said first mentioned circuit being so chosen that its terminals are at node potential relative to the image frequency of said receiver, and a capacity of said link circuit so selected that said link circuit is resonant to a frequency outside the band of frequencies tol Which it is desired to tune said receiver.

6. A signal selecting device for a radio frequency receiver which comprises a circuit tunable to a current of the frequency it is desired to receive including an inductance and a capacity, a second circuit likewise tunable to the frequency of the current it is desired to receive also including an inductance and a capacity, and a link circuit connecting a portion of the inductance of said first mentioned circuit and including an inductance which is inductively related to the inductance of said second mentioned circuit, the portion of the inductance of said first mentioned circuitV being so chosen that its terminals are at node potential relative to a specific frequency which it is not desired to receive.

7. A radio signal selecting circuit for a frequency as the circuits are tuned, said link circuit includin an inductance inductively related to the high potential Vend of the inductive reactance of said second tuned circuit whereby the coupling between said tuned circuits includes the mutual inductance between the inductance of said link circuit and the inductive reactance of said second circuit and the inherent capacity between said inductances.

8. A signal-selecting device for a radio receiver which comprises a circuit tunable to a current ofthe frequency it is desired to receive, including an inductance and a capacity, a second circuit likewise tunable to the frequency of the current it is desired to receive also including an inductance and a capacity, and a link circuit connected to a portion of the inductance of` said first mentioned circuit and including an inductance of relatively high impedancewhich is inductively related to the inductance of said second mentioned circuit, the portion of the inductance lof said first mentioned circuit being so chosenthat its terminals are at node potential relative to a specific frequency which it is not desired to receive, said circuits being so proportioned that substantially optimum coupling will be had between said first and said second mentioned circuits.

9. A signal selecting device for asuperheterodyne radio receiver which comprises a circuit tunable to a current of the frequency it is desired to receive, including inductive and capacitive reactances, a second circuit likewise tunable to the frequency it is desired to receive also including inductive and capacitive reactances, and a link circuit connected toa portion of the reactances of said first mentioned circuit and including a relatively high inductance inductively related yto the inductive reactance of the second mentioned circuit, the portion of the reactance of said first mentioned circuit being so chosen that its terminals are at node potential to the image frequency of said receiver, said circuits being so proportioned that the gain of said second mentioned ycircuit will permit optimum coupling regardless of the loss occasioned by tapping off only a portion of the desired signal voltage available in said rst mentioned circuit.

10. A signal selecting device for a radio receiver which comprises a circuit tunable to a current of the frequency it is desired to receive including an inductance and a capacity, a second circuit likewise tunable to the frequency of the i current it is desired to receive, and also including an inductance and a capacity, a link circuit connecting a portion of theinductance of said first mentioned circuit and including an inductance which is inductively related to the inductance of said second mentioned circuit, the portion of the d inductance of said first mentioned circuit be ing so chosen that its terminals are at node potential relative to a specific frequency which it is not desired to receive, and a capacity in `said link .circuit so selected'that -said link circuit is resonant to a frequency below the band of frequences to which it is desired to tune said receiver.

11. Radio signal selective circuits for superheterodynel radio receivers which com-v prise two radio frequency circuits tunable to the frequency of the current it is desired to receive, each including inductive and capacitive reactances, a link circuit connected across a port/ionof the reactance of one of said tuned'circuits so selected that the terminals of said link circuit'are at node potential relative to a current of the image frequency and including an inductance inductively related to the high potential end of the inductive reactance .of the second of said tuned circuits whereby the coupling between said tuned circuits includes the mutual inductance between the inductance of Said link circuit and the inductive reactance of said second mentioned circuit and the inherent capacity between said inductances, the winding of said inductances being so arranged that the mutual inductance coupling will oppose the capacitiveY coupling between the link circuit and the second of said circuits, thus providing a lesser response at the high frequency portion of the tuning range of said circuits.

12. A radio signal selecting device for a radio receiver which comprises two radio frequency circuits tunable to the frequency of the current to be received by said receiver, each including an inductance and a capacity, a link circuit connected across a portion of the inductance of the first of said tunedL circuits so selected that the terminals of said link circuit are at node potential relative to the current of an undesired frequency, said link circuit including an inductance inductively related to the high potential end of the inductance ofY said second tuned circuit whereby the coupling between said tuned circuits includes the mutual inductance between the inductance of said link circuit and the inductance of said second mentioned circuit and the inherent capacity between said inductances.

13. A radioreceiving apparatus of the superheterodyne type including signal selecting s circuits'comprising two circuits tunable to the Yfrequency of the current it is desired to re- `ceive, each -including inductances and capacities yand a link circuit effec-tively connected across at least a portion of the inductance of each of said circuits and including a capacity, the portion of the inductance' of the rst of said tuned circuits being so chosen that the terminals of said link circuit are at node potential relative to a current of the image frequency of said receiver and the portion of the inductance of the second tuned circuit being so chosen that the voltage gain insaid circuit will compensate for the loss due t0 the rejector action of the first circuit, and the capacity of said link circuit being so selected that said circuit will be resonant to a frequency outside the-band of frequencies which it is desired to receive.

14. A radio signal selective device fr radio receivers which comprises two radio frequency circuits tunable to the frequency of the current it is desired tok receive, each including an inductance and a capacity, a link circuit connected across a portion of the inductance of one of said tuned circuits so se.

lected that the terminals of said link circuit are at node potential relativeto current of an Vundesired frequency and including an inductance inductively related to the high potential end of the inductance of the second of said tuned circuits whereby the'coupling between said tuned circuits includes the mutual inductance between the inductance of said link v,circuit and the 'inductance of said second mentioned circuit and the inherent capacity between said inductances, the winding ofsaid inductances being so arranged that the mutual inductance coupling will oppose the capacitive couplingbetween the link circuit and the second of said circuits, thus providing a lesser response at the high frequency portion of the tuning range of said circuits.

15.- A radio frequency tuning system for a radio receiver of the superheterodyne type which comprises two circuits tunable to the frequency of the current itis desired to receive, each circuit comprising inductive and capacitive'reactances, and a link circuit connected' to lsaid tuned circuits, including a portion of the inductance of each of said circuits, that portion of the inductance ofthe first of said circuits beingpso selected that the terminals of said link circuit will remain at substantally node potential relative to a current of the image frequency of said receiver as the circuits are tuned, and said link circuit including an open end winding inductively and capacitively related to the inductance of the second of said circuits whereby said link circuit comprises the capacitive coupling between said open end winding a-nd the inductance of said second circuit and a portion of the inductance's of each ofsaid tuned circuits.

16. A radio frequency tuning system comprising two circuits tunable tothe frequency of the current it is desired to receive, each comprising inductive and capacitive reactances, and a link circuitconnecting said tuned circuits including a' portion of the inductance of the firstof said circuits so selected that the terminals of said link circuit are at node po- -tential relative to a current of an undesired ductively and capacitively related to the inductance of the second of said circuits, Whereby said link circuit comprises the capacitive coupling between said open end winding and the inductance o said second circuit and a portion of the inductance of the first circuit.

In testimony whereof I aiix my signature.

A J. KELLY JOHNSON.