US2116713A - Radio receiving system - Google Patents

Description

May 10, 1938.. J, D REID RADIO RECEIVING SYSTEM Filed sept. 30, 1955 INVENT' John .Heia

HT'T' .U Si

Allin Patented May 10, 1938 UNITED STATES PATENT OFFECE RADIO RECEIVING SYSTEM of Delaware Application September 30, 1935, Serial No. 42,903

16 Claims.

My invention relates to a radio receiving system. More specifically my invention relates to a simplified all wave superheterodyne receiver in which the first detector and local oscillator may 5 be combined in a multi-purpose thermionic tube.

The development of the circuits for superheterodyne radio receivers has been progressing toward simplicity of parts and wiring. The use of higher frequencies for broadcast transmission l has brought about the design of many all wave receivers. These receivers are characterized by a plurality of tuning inductors and capacitors which require most complicated switching means with resulting complication of wiring. Thus no l small part of the approach to a simplified superheterodyne has been lost in the development of the all wave receiver.

Receiver development has been accompanied by improvements in thermionic tubes. The

tubes have, for example, been simplified by the inclusion and combination of several electrodes in a single envelope to serve several functions. These tubes are called multi-purpose tubes. Although the multi-purpose tube has decided benefits at low frequency, difficulties have been eX- perienced at the higher frequencies. I propose to overcome these, and other difficulties, by the present invention which may be best understood by reference to the accompanying drawing and specification.

One of the objects of my invention is found in the simplified means for selectively choosing any one of a plurality of frequency ranges.

Another object is the method of avoiding the degenerative effects of a combined first detector and. local oscillator tube.

A further object is the means employed to avoid fluttering or overall audio feedback, and ripple effects which are troublesome in super- 40 heterodyne circuits.

A still further object is in the method of coupling the antenna system to the all wave receiver embodying my invention.

Additional objects will be found in the accompanying specification and claims.

In the accompanying drawing is shown a schematic diagram of one embodiment of my invention applied to an all wave superheterodyne. The intermediate frequency amplier, the second demi tector and automatic volume control, the audio frequency amplifier, the loudspeaker, and the power source of rectified, filter current are not part of my invention, per se. These several elements are well known to those skilled in the art ed and do not require detailed illustration.

In the accompanying schematic diagram an antenna I is connected to the primary 3 of a radio frequency transformer 5. The inductance of the primary is preferably chosen so that, with the antenna capacity and its ofwn inherent capacity, it will resonate within the tuning range of the middle frequency band of the receiver. On the rst or lowest frequency band, a capacitor 'l and resistor 9 are serially connected across the primary. The capacitor lowers the resonant fre- 3g quency of the primary to a value within the lowest frequency band of the receiver. A series circuit II, resonant to the frequency of the intermediate frequency amplifier, is shunted across the primary to attenuate voltages of interfering 15 signals.

The secondary of the radio frequency transformer is composed of three windings I3, I5, I1 which are used respectively in the high, medium and low frequency band of the receiver. The first and second of these windings I3, I5 are mutually coupled to the primary 3.

A single section, three position range switch I8 is connected to selectively choose the desired operating range. In this switch contact arms 2U move over a grounded commutator 22. In this 5 switch the first three contacts I9, 2l, 23 are connected to the proper inductors and capacitors for the low, medium, and high frequency ranges. The first Contact I9 connects the capacitor 1 and resistor 9 across the primary. The capacity tunes the primary to a frequency within the low range. The resistor II dampens the primary circuit and prevents undesirable reactions with the tuned secondary circuit. The secondary circuit on the 3- low range is composed of the three secondary windings, I3, I5, I'I, which are serially connected, a trimmer capacitor 24 across the third of these windings, and a Variable capacitor 25 which has a parallel connected trimmer capacitor 21. The 40 variable capacitor 25 is grounded; the third secondary winding I'I is grounded, and thus the lowrange secondary circuit is grounded. A thermionic radio frequency amplifier 29 is connected across the secondary circuit by a blocking capac- 45 itor 3I which connects the high potential terminal cf the secondary circuit to the control grid 33 and by the grounded cathode of the amplifier 29. The control grid is biased by a direct current potential derived from the automatic volume control rectifier.

The medium frequency range 1s chosen by placing the range switch on the second contact 2|. In this position the range switch disconnects the capacitor l which shunts the primary. The

I sistor 49.

*".'. a capacitor 61 and a series resistor 69.

effect of removing this capacity is to tune the antenna or primary circuit within the range of the medium range. The third secondary winding I1 is short circuited and grounded. The secondary inductance is composed of the rst and secondary windings I3, I5. The tuning capacitance is made up of the variable capacitor 25 and the trimmer capacitor 21.

The high frequency range is chosen by moving the range switch to the third contact 23. In this position the antenna or primary circuit is tuned to a frequency lower than the lowest frequency within the high frequency range. The secondary circuit is composed of the rst secondary winding I3 which is connected to ground through a tracking capacitor 35. The function of the tracking capacitor will be described below. The reactance of the remaining secondary windings I5, I1 is negative at the high frequencies of this range and its effect is to increase the capacity of the tracking capacitor.

The output circuit of the radio frequency amplifier is of the low impedance type. The anode circuit within the tube is made of low impedance by joining the screen electrode 31 to the anode 39. The anode is connected to the primary 4| of a radio frequency transformer 43. The primary is also connected to the positive terminal 42 of the B voltage source |21. The inductance of the primary is chosen so that with its associated capacity it will resonate at a frequency just below the lowest frequency of the high frequency range. A damping resistor 45 is shunted across the primary to avoid pronounced resonance peaks.

On the low frequency range the range selector switch is positioned on terminal 54 which is grounded by arm 20 so that the primary 4| is effectively shunted by a capacitor 41 and a re- The combined effect of these elements is to tune the primary to a frequency within the lowest frequency range and further damp its resonant peak. The secondary of the transformer 43 is made up of three secondary windings 53, 55 which are serially connected. The first two windings 5|, 53 are mutually coupled to the primary. A trimmer capacitor 51 is shunted across the third winding 55. The tuning is accomplished by a variable capacitor 59 which is shunted by a trimmer capacitor 6|. The variable capacitor is grounded.

The high potential terminal of the secondary circuit is connected to the control grid 63 of the rst detector and local oscillator tube 65 through The junction between the capacitor 61 and the series resistor 69 is connected through a grid resistor 1I to the negative terminal of the automatic Volume control means. The output circuit comprises the anode 13, a resonant circuit tuned to the intermediate frequency, and a connection to the positive terminal 42 of the B current source |21.

When the range switch is placed on the contact 2| which is selected for the medium frequency range, the terminal connection 54, which shunts the capacitor 41 and series resistor 49 across the primary 4|, is opened. The primary 4i without the shunt capacity resonates within the medium frequency range. The third secondary winding 55 is short circuited by the range switch arm which grounds terminal 25. The secondary inductance in the medium range is composed of the rst and second windings 5|, 53. The adjustable tuning capacity is made up of the inherent capacities of the circuit and the variable capacitor 59 with its trimmer 6|. The secondary circuit is coupled to the first detector and mixing tube 05 as described above.

In the high frequency range the primary tunes below the lowest frequency of the high frequency tuning range. Its resonant peak occurs at a frequency which is close to the range, and has an effect which is substantially equalled by the tracking capacitor previously mentioned. The second and third windings 53, are short circuited by contact arm 20 which grounds terminal 28. The secondary circuit of transformer 43 is tuned by the variable capacitor 59 and the inherent capacities associated with the circuit.

The local oscillator is comprised of a cathode 11, grid 19, and anode 8| which electrodes are includede within the envelope of the first detector 65. The cathode is grounded. The grid is connected through a grid capacitor 83 to the high potential terminal of a variable capacitor 85 which is shunted by a trimmer capacitor 81 and grounded. The grid is connected to a grid leak resistor 89 which is grounded.

Three inductors 9|, 93, 95 comprise the inductance of the grid circuit. Of these inductors, the high potential terminal of the rst inductor 9| is connected to the variable capacitor 85. The low potential terminal of the first inductor 9| is connected by means of a commutator 91 to an insulated movable blade 99 of the range switch I8. The second inductor 93 has its low potential terminal grounded and its high potential terminal connected to the contact 46 of the range switch. The third inductor 95 has its high potential terminal connected to the range switch contact 44. A trimmer capacitor I 0| connects from the high potential terminal of this inductor 95 to ground. The low potential terminal of the third inductor 95 is connected to ground by tracking capacitor |03.

The anode circuit of the oscillator includes two inductors |05, |01. The rst of these inductors |05 is connected to the anode 8| and to the positive terminal 42 of the B voltage source |21 through a radio frequency choke |09 and a filter network |I5I I1 which will be described below. This inductor |05 is also mutually coupled to the rst grid circuit inductor 9| and through a blocking capacitor to the second anode inductor f |01. The second anode inductor |01 is connected through the tracking capacitor |03 to ground. This common capacity |03 connection is also the feed back connection for the low frequency range of the oscillator. The second anode inductor |01 is mutually coupled to the second grid circuit inductor 93 for feedback at the medium frequency range.

On the low frequency range the grid circuit of the oscillator is tuned to the signal frequency plus the intermediate frequency, which may be 460 kilocycles by way of example. The grid circuit is comprised of the first and third inductors 9|, 95, shunt trimmer capacitors 81, |0I, the variable capacitor 85, and the series tracking capacitor |03. The feedback is primarily through the tracking capacitor |03 which is common to the grid and anode circuits. This common capacitor |03 increases the effective coupling as the frequency is decreased. 'I'he anode circuit is composed of the two anode circuit inductors |05, |01 which are connected by the blocking capacitor The mutual coupling between the first grid inductor 9| and the first anode inductor |05 tends to incr-ease the feed- CII back at the higher oscillator frequencies. The second anode inductor |01 increases the load in the anode circuit.

The oscillator for the medium or middle frequency range has a grid circuit which is cornposed of the first and second grid inductors 9|, 93 and the variable and fixed capacitors 85, 81. The anode circuit is composed of the two anode inductors |85, |81. The second of these inductors is mutually coupled to the second grid inductor 93. It will be observed that the usual tracking capacitor is omitted. The omission of the tracking capacitor is possible because the effect of the radio frequency primary 4 I which is tuned Within the medium range, is to gradually decrease the resonant frequency of the detector input circuit as it is tuned to higher frequencies. Also `the tuning of the detector input circuit becomes relatively broad, as the resonant frequency of the primary III. which is highly damped with resistor 45, is approached. Therefore, the tracking is less critical in the region of the resonant frequency of the primary. This condition exists at the high frequency end of the detector input circuit. A similar condition obtains at the low frequency end of the radio frequency input circuit due to the resonant frequency of the antenna circuit. Thus by properly proportioning the inductors I5, 53. satisfactory tracking may be obtained without the use of series tracking capacitors. The omission of series capacitors permits a wide frequency range to be covered. The oscillator per se is made to oscillate at a frequency equal to the signal frequency plus the intermediate frequency. In this medium frequency range the third grid inductor 95 of the oscillator is shortcircuited, by the connection of terminal 36 and arm 2!) of range switch I8, to avoid undesired reactions.

It will be observed that the oscillator for the low and middle frequency ranges has been adjusted to operate at frequencies which are higher than the signal frequency by the amount of the intermediate frequency. It has been the practice by those skilled in the art to follow the same practice at the higher frequency ranges, for example, above six megacycles. Where the first detector and oscillator tubes are combined in a single envelope, the oscillator reacts in an anti-regenerative sense on the rst detector when the oscillae tor frequency is higher than the detector frequency` This anti-regenerative effect or degeneration is probably due to some inherent capacity coupling or the like between the oscillator electrodes and the control grid electrode. In the presence of such capacity, if the oscillator circuit is tuned to a higher frequency than the signal, the control grid circuit will be a capacitive reactance and produce degenerative effects.

I have found that these effects, which greatly attenuate the incoming signal may not only be avoided but the incoming signal may be greatly amplified by making the control grid circuit inductive with respect to the tuned oscillator circuit.

This is the proper condition for regenerative rather than degenerative effects. Under some conditions the first detector may tend to oscillate at the higher frequencies. A relatively low value of resistance serially connected to the control grid will overcome this tendency and still preserve the signal amplification.

The inductive effect is brought about by the simple expedient of tuning the oscillator to a frequency equal to the signal frequency minus the intermediate frequency in the high frequency range. The grid circuit of the oscillator in the high frequency range is composed of the first grid inductor 9|, the trimmer capacitor 81, and the variable capacitor 85. The anode circuit is composed of the rst anode inductor which is mutually coupled to the rst grid inductor. The junction between the blocking capacitor I II and second anode inductor |01 is grounded in this range by the range switch I8.

Since the oscillator frequency on the high frequency range is maintained at a constant frequency below the radio frequency and detector input circuits, no series tracking capacitor is used in the oscillator. In place of the usual oscillator tracking capacitor, a series tracking capacitor 35 is employed in the radio frequency input circuit. This capacitor keeps the radio frequency input circuit at the required constant frequency` above the oscillator frequency. A series tracking capacitor is not required in the detector input circuit because of the effect of the primary 4 I. This primary is resonant below the low frequency end of the high frequency range, and as its resonant frequency is approached, the primary reduces the rate of change of frequency of the detector input circuit. This effect is equivalent to the series tracking capacitor 35 in the radio frequency input circuit and is used to make the several circuits track properly.

It should be noted that the oscillator anode and screen grid are both connected to the same positive terminal of the power supply. The voltage to the screen grid is reduced by a series resistor H3. A second series resistor I I5 and grounded capacitor II1 act as an effective audio frequency lter. If the potential of the positive source varies, the filter will greatly attenuate these variations which become most serious on the high frequency ranges. Moreover the oscillator anode and the screen grid have opposing effects which tend to neutralize the effect of voltage variations and thereby prevent power supp-1y ripple or nutter. The term flutter is used to describe overall audio frequency fluctuations which are fed from the audio amplifier to the oscillator and repeated through the system. Because of the excellent filtering and comparative freedom of the oscillator anode and oscillator screen potential from audio frequency variations, I have found that this terminal IIS is a suitable junction for anode potential of the first audio amplifier.

In the diagram I have omitted a detailed showing of the heater circuits, and the automatic Volume control circuits. These connections are indicated but are not completed. This omission simplifies the diagram. The output of the first `detector and local oscillator may be fed to an intermediate frequency amplifier IIS, and hence to a second detector and A. V. C. circuit I2 I The output of the second detector may be amplified by an audio amplifier |23 and reproduced by a loudspeaker |25. A power source |21 for the system may be batteries, alternating current, which may be rectified and filtered, or the like. I have mentioned the terms high, medium or middle, and low frequency ranges, which may cover, respectively, the following ranges: 6 to i8 megacycles, 1.6 to 6 megacycles and 540 to 1000 kilocycles.

It should be noted that the variable capacitors 25, 59, 85 are conected to a single control. Each of these Variable capacitors is shunted by trimmer capacitors which align the tunable circuits in the high and medium frequency ranges. The use of a single trimmer for the two ranges is effected by choosing inductors which are carefully held to the proper values of inductance and distributed capacity. Additional trimmer capacitors are preferred in the low range as it would be difficult and expensive to manufacture the inductors of larger value to the exactness required if trimmers were to be omitted.

I have described a radio receiving system which effectively covers three ranges of frequencies, and in which the antenna is effectively coupled on all frequency ranges. The oscillator has been made to overcome serious degenerative effects by substituting a regenerative gain for the degenerative loss. The circuit connections and filter arrangements prevent fluttering. Nu-

merous modifications Within the scope of my invention will occur to those skilled in the art. It should be understood that I do not intend to limit my invention except as required by the prior art and the appended claims.

I claim as my invention:-

1. In a multi-range radio receiver responsive to low and medium frequency ranges, an antenna system including a primary circuit resonant to a frequency within the medium frequency range of said receiver, a secondary circuit including means for resonating said secondary circuit over said frequency ranges, means for mutually coupling said primary circuit and secondary circuit, switching means including connections to said secondary circuit for selecting a desired range of said ranges, and means connected to said switching means and said primary circuit for resonating said primary circuit to a frequency within the low frequency range of said receiver upon selection of said low frequency range.

2. In a multi-range radio frequency receiver responsive to low, medium, and high frequency ranges, an antenna system including a primary circuit resonant to a frequency within the medium range of said receiver and mutually coupled to a secondary circuit, a secondary circuit coupled to said primary circuit and including means for resonating said secondary circuit over each of the said frequency ranges, means connected to said secondary circuit for selecting any one of said ranges, and means connected to said selecting means and to said primary circuit for tuning said primary circuit to a frequency within the low frequency range upon selection of said low frequency range.

3. In a radio receiver tunable over low, medium and high frequency ranges, an antenna system including a primary circuit resonant to a frequency within the medium range of said receiver, a secondary circuit including means for tuning said secondary circuit over said low, medium and high frequency ranges, means for mutually coupling said primary circuit and said secondary circuit, switching means connected to said secondary circuit for selecting any one of said ranges, and means connected to said switching means and said primary circuit for tuning said primary circuit to a frequency within the low frequency range of said receiver upon selection of said low frequency range.

4. In a radio receiver tunable over low, medium, and high frequency ranges, an antenna system including a primary circuit resonant to a frequency within said medium frequency range and mutually coupled to a pair of inductors, a lpair of inductors, a secondary circuit including said pair of inductors and means for tuning said secondary circuit over each of said plurality of ranges, switching means connected to said secondary circuit for selecting a desired one of said ranges, and means connected to said switching means and to said primary circuit for resonating said primary circuit to a frequency within the lowest range of said plurality of ranges upon selection of said low frequency range.

5. A device of the character of claim l including means for broadening the resonant response of said primary circuit and means for attenuating interfering signals in said primary circuit.

6. In a device of the character of claim 1, means for broadening the resonant response of said primary circuit in said low frequency range.

7. In a multi-range radio receiver responsive to low, medium and high frequency ranges, a radio frequency amplifier whose output circuit includes a primary circuit resonant to a frequency below the lowest frequency of said high frequency range, a secondary circuit tunable over each of said frequency ranges, means for mutually coupling said primary and secondary circuits, switching means connected to said secondary circuit for selecting a desired one of said ranges, and means connected to said primary circuit and to said switching means for tuning said primary circuit to a frequency within the low frequency range of said receiver upon selecting said low frequency range.

8. In a radio receiver tunable over low, medium and high frequency ranges, a radio frequency amplier including a primary output circuit resonant within the medium frequency range of said receiver and mutually coupled to a pair of inductors, a pair of inductors coupled to said primary circuit, a secondary circuit including said inducM tors and means for tuning said secondary circuit over each of said frequency ranges, means connected to said secondary circuit for selecting one of said ranges and means connected to said primary circuit and to said selecting means for tuning said primary circuit to a frequency within the low frequency range for reception of signals in said range.

9. A multi-range radio receiver tunable to low, medium and high frequency ranges including a radio frequency amplifier having a primary output circuit tuned to a frequency within the medium range of said receiver and coupled to a secondary circuit, a secondary circuit coupled to said primary circuit and including means for resonating said secondary circuit over each of said low, medium and high frequency ranges, switching means connected to said secondary circuit for selecting one of said ranges, and means connected to said primary circuit and to said switching means for resonating said primary to a frequency within the low frequency range of said receiver upon selection of said low frequency range.

l0. In a device of the character of claim 7, means for broadening the tuning of said primary circuit upon selection of said low frequency range.

ll. In a device of the character of claim '7, means for broadening the tuning of said primary circuit on all frequency ranges and additional means for broadening the tuning of said primary circuit upon selection of said low frequency range.

l2. In a multi-range radio receiver tunable over low, medium and high frequency ranges, an antenna system including a primary circuit normally resonant to a frequency within said medium frequency range and coupled to a secondary circuit, a secondary circuit coupled to said primary circuit and tunable over several frequency ranges, switching means connected to said secondary circuit for selecting any of said ranges, a radio frequency amplifier having a primary output circuit including elements resonant to a frequency Within said medium frequency range and coupled to a second secondary circuit, a second secondary circuit coupled to said amplifier output circuit and tunable over said frequency ranges, switching means connected to said second secondary circuit for selecting one of said frequency ranges, and means connected to said first mentioned primary circuit and to said switching means for resonating the firstmentioned primary to a frequency within the low frequency range of said receiver and means connected to said second mentioned primary circuit and to said switching means for resonating the second-mentioned primary to a frequency within the low frequency range of said receiver upon selection of said low frequency ranges.

13. In a radio receiver tunable over low, rnedium and high frequency ranges, an antenna system including a primary circuit resonant to said medium frequency range and coupled to a tunable secondary circuit, a secondary circuit tunable throughout said frequency ranges and coupled to said primary circuit, means operable upon selection of said low frequency range for resonating said primary circuit to a frequency within the lowest range of said plurality of ranges, a single thermionic tube including means for generating local oscillatory currents and means for demodulating'received oscillatory currents, means resonant to incoming signal frequencies effectively connected to said demodulator means, means resonant to lower frequencies than said resonant means connected to said demodulator means eiectively connected to said means for generating local oscillatory currents so that the resonant means connected to Said demodulator is inductively reactive with respect to the resonant means connected to said generator throughout one of said frequency ranges, and means connected to said secondary circuit, to said demodulator means, and to said means for generating local oscillations for selecting any one of said ranges.

14. In a device of the character described tunable over low, medium and high frequency ranges, an antenna circuit resonant to a frequency within the medium frequency range of said device, a

secondary circuit coupled to said antenna circuit and including means for resonating said secondary circuit over a plurality of frequency ranges, means operable upon selection of said low frcquency range for tuning said antenna circuit to a frequency within the lowest frequency range of said device, a radio frequency amplifier connected to said secondary circuit and including a primary circuit resonant to a frequency within said medium frequency range, means operable upon selection of said low frequencyrange to resonate said primary circuit within said low frequency range, a second secondary circuit tunable over said frequency ranges, means coupling said last-mentioned primary circuit and the last-mentioned tunable secondary circuit, a single thermionic tube including means for generating local oscillatory currents and means for demodulating received oscillatory currents, connections from said demodulator means to the last-mentioned tunable secondary circuit and a tunable circuit resonant to a lower frequency than incoming signal frequencies in the highest frequency range of said receiver effectively connected to said generator of local oscillations for generating an intermediate frequency.

15. In a device of the character of claim 14, a single section of switching means for simultaneously selecting the desired frequency range in each of said tunable circuits.

16. In a superheterodyne receiver, a single thermionic tube having local oscillator electrodes and detector input electrodes and a screen grid interposed between said detector and oscillator electrodes, means resonant to incoming signal frequencies effectively connected to said detector input electrodes, means resonant to lower frequencies than said first mentioned resonant means effectively connected to said local oscillator electrodes whereby the first mentioned resonant means is inductively reactive with respect to said second mentioned resonant means, said screen grid electrode substantially reducing the coupling effect of said circuits upon each other, and additional resistive means serially connected between said first mentioned resonant means and said detector input electrodes of such value as to complement the shielding effect of said screen grid whereby self oscillations are suppressed.

JOHN D. REID.

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