US1875837A - Radio receiving apparatus - Google Patents

Description

Sept. 6, 1932. v H. A. WHEELER 1,875,837

RADIO RECEIVING APPARATUS Filed Jul 7, 1951 INVENTOR HAROLD 4. WHL-ELER Mw W ATTORNEYS Patented Sept. 6, 1932 t 1,875,837

UNITED STATES PATENT OFFICE HAROLD A. WHEELER, OF GREAT NECK, NEW YORK, ASSIGNOR TO HAZEL' IINE CORPORATION RADIO RECEIVING APPARATUS Application filed July 7, '1931. Serial .No. -549,149.

The present invention relates to the seleccurrent with a consequent loss of the signal tion of a radio-frequency signal being transenergy. mitted on one carrier frequency and the It is therefore another ob ect of the pressimultaneous reduction of interference being ent invention to provide an improvedradio transmitted on other frequencies not greatly receiving apparatus in which the attenuation different from the frequency of the desired of the image frequency obtainable by ign l, means of the tapped coil just described may The invention is particularly applicable to be had, and yet one in which there will be no a superheterodyne type of receiver. It is ultimate loss in amplification or gain incident 10 Well known that the superheterodyne is sensito the rejector action. tive to signals of two frequencies when set to These and further objects will be apparent receive any given frequency. The two fre- 1n connection with the following description quencies differ from each other by twice the when considered in connection with the drawamount of the off-set or intermediate freing. 5 quency to which the intermediate-frequency In accomplishing the objects of the invenamplifier is permanently tuned. tion, a signal selecting system is provided It is a common practice to employ a signal comprising an input transformer having a' selecting system to amplifygthe desired fretuned secondary, the tuning of which may be quency of the two carrier frequencies to which varied to cause the tuned circuit to respond 30 the superheterodyne receiver responds, the to frequencies covering the broadcast band, desired frequency herein being called the sigfor instance. The secondary of said transnal frequency, and which s gnal selecting sysformer is tapped at such a point that the tem attenuates the undesired Carrier unused portion of the transformer together quency or disturbance occurring atthe other with the tuning condenser will constitute a frequency, herein called the image freby-pass to currents of the 'mage frequency. quency. In other words, the termi als'of the tapped I The relativeattenuation of the image file inductance will be at node potential relative quency can be increased by simultaneously to the. signal frequency. The tapped portion tuning several selective circuits to the signal of th in ut inductance is connected with a 30 frequency. H W V I, if th i n H second tuned circuit comprising an inducmitting at the image frequency comes in tance and capacitance, by means of a link cirrather strong, it is difficult to differentiate beit, hi h i lud a, portion of thecapacitween the signal and image,frequencie tive reactance of-the second tuned circuit. It is the object of the present inventi n to A capacity may also be included in the link 35 Q? this d1sadvantage 111 P circuit for the purpose of causing it to reheterodyne r v spond to a current of a definite frequency, To accomplish this object it. is proposed to as may be desired. The. inductance of the attenuate the undesired image frequency by d t d i it may b t d i a i ithe use of a special rejector circuit comprising 1 ann r to provid for further image 40- an input transformer of which the secondary frequency reduction. is tapped to constitute the connection to the H i thu briefly described the inveninput of the radio-frequency amplifier or of tion,attention isinvited tothe accompanying the first detector in a manner similar to that drawing which shows a selective circuit em- I disclosed in U. S. Patent No. 1,680,424, issued bodying the present invention. August 14', 1928, to W lliam A. MacDonald. The antenna or input circuit comprises The tap is so selected that the terminals of antenna 1, ground terminal 2, and the prithe portion of the secondary coil are at node mary coil 3. The first tuned circuit comprises potential relative to currentspf the image secondary coil. 4 and} variable tuning confrequency. However, such a system results denser 5, the secondary coil {1 being coupled in the by-passing of a portion of the signal to the primary coil 3. The second tuned cirtuned circuits are above the signal frequency.

age at the ,means of the common ground connection and the coupling condenser 7 connected between the intermediate tap 6 on coil 4 and the series condenser 8. The intermediate tap 10 of coil 9 may be in turn connected to the grid or inut terminal of a superheterodyne system of which only the vacuum tube 12, which may be the first detector or radio frequency amplifier,

is indicated. Tuning condensers 5 and 11 may have similar electrical characteristics and be arranged for uni-control, as indicated in the drawing, as by mounting on the same shaft.

The antenna coil 3 is coupled mostly to the lower part of the coil 4, according to any satisfactory arrangement, manyof which are commonly used. The two simultaneously tuned by means of the tuning condensers to the sigwhich may be, for instance,

that is, 550 to 15.00 kilocycles. The superheterodyne system is usually designed so that the image frequency lies above the signal frequency and may fall within the range of 900 to 1850 kilocycles, in case the intermediate frequency is 17 5 kilocycles. vWhen the first tuned circuit is tuned as a whole to the signal frequency, the upper part of coil 4 and the condenser 5 form a resonant rejector circuit between tap 6 and the ground; The

, rejector circuit contains a smaller inductance of the entire tuned circuit and is always resonsant to a frequency By proper location of the tap 6 on coil 4, the rejector circuit canv be made to tune over approximately. the image frequency range. When the entire circuit'4, 5 is tuned over the broadcast band with the tap 6 at such a point as to give about 45% of the'voltage existing across the entire coil ,4, the rejector circuit will tune over a range offrom 750 to 2040 kilocycles. With a uniformly wound helical coil, 45% of the voltage-would .be obtained if the output included about 45% of the total number of turns in the coil. It is to be noted that this gives approximately the image frequency than that therefore I range given above: The rejector circuit 1s,

with a 45% tap, tuned exactly to the image I frequency of 1320 kilocycles when the signal frequency is 970 kilocycles.

The rejector circuit arranged with the roper location of tap 6 therefore greatly lncreases the attenuation of the .image frequency as-measured at tap 6. It canvconsequently be seen that the voltage-gain characteristic curve of the portion of the secondary 4 below the tap 6'will show zero voltimage frequency, whereas the naturalresonance of the circuit 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 of the tapped portion of the coil 4. 'It is desirable to couple circuit 4, 5 and circuit 9, 11 by an amount somewhere near .the optimum value, which may be between 0.5% and 1%. This may be accomplished by making the capacity of .the condenser 7 of the order of the minimum capacity of the circuit 9, 11 and making the. capacity of the condenser 8 several times greater than the maximum of the capacity of the circuit 9, 11. There is no additional gain when this coupling is greater than optimum. Therefore,

no loss of sensitivity results from coupling the upper end of coil 4. There is also the definite advantage of the greater imagefrequency attenuation obtainable by taking the voltage The second circuit 9, 11 is tuned to the signal frequency, and may or may not employ a tap connection similar to tap 6 on coil 4. A similar tap 10 is shown in the diagram which would result in further increase in the attenuation of the image frequency. It is to be noted that the presence or absence of tap 10 does not afiect the advantage to be gained by use of tap 6. Tap 10 has the disadvantage .of reducing the signal voltage output from circuit 9, 11 although the imagefrequency-reduction is more than the signalfrequency reduction.

It is convenient to refer to tap 6 as a-node point relative to ground for theimage-frequency current since there is approximately from tap 6, as described above. 7

zero image-frequency voltage between this several useful and operative alternatives are known'in the art. The essential feature is that the second tuned circuit is coupled to the first by means responsive to signal-frequency currents in the first tuned circuit and unresponsive to image-frequency currents in the first tuned circuit. The preferred embodiment described herein-includes in such means, the tap 6 for attenuating imagefrequency currents and condensers 7 and 8 for conducting the signal-frequency currents.

What I claim is:

1. In a superheterodyne radio receiver, means for rejecting the image frequency, which comprise an input transformer, a tuned radio-frequency circuit including the secondary of said transformer, a second tuned radio-frequency circuit, and means connecting said tuned radio-frequency circuits, said last mentioned means including a connection to a portion of the first tuned circuit which the image frequency.

2. A radio-frequency tuning arrangement for a radio receiver, which comprises a cir cuit tuned to a current of the signal frequency, a secondcircuit tuned to the same frequency, a coupling circuit connecting said circuits, said coupling circuit being connected across a portion of the impedance of the first mentioned circuit, the terminals of which portion are at node potential relative to current of an undesired frequency and across a portion of the impedance of the second mencurrent with a first circuit upon tloned circuit.

3. In a superheterodyne recelver means for rejecting the image frequency which comprise a circuit resonant to the signal fre quency, a second circuit resonant to the signal frequency, circuits connected at points in the first of said circuits which are at node potential relative to currents of the image frequency and connected across a part of the capacitive reactance of the second of said circuits, whereby the current of the. image frequency is attenuated and the gain in amplification of the desired signal frequency current lost in said first mentioned circuit is compensated for by gain in amplification of said current in the second tuned circuit.

4. The combination of an electrical system responsive to a desired frequency and to an undesired frequency, which comprises a first which are impressed signals of both of said frequencies, a second circuit connected to said system, both of said circuits being individually resonant to currents of the desired frequency, said first circuit including two points which are node points for currents of the undesired frequency, and a coupling circuit connected to said two points and coupled to said second circuit whereby sig nals having said undesired frequency are greatly attenuated.

5. Thecombination of an electrical system" responsive to desired and undesired frequency which are impressed currents of desired and undesired signal frequencies. a second circuit, said first and second circuits being individually resonant to currents of the desired signal, said first circuit having two points which are node points for currents of the undesired frequency, and a coupling circuit connected to said two points and coupled to said second circuit whereby signalshaving said undesired frequency are greatly attenuated, said coupling circuit providing substantially optimum coupling between said first and second circuits, whereby the attenuation of currents of said desired frequency is reduced to a minimum.

6. An electrical network adapted to select any desired frequency within a predetermined range and to simultaneously reject an undesired frequency which differs from said de- .being adapted to receive and means connecting said a radio responsive device and sired frequency by a constant difference frequency, which comprises in combination an input circuit, an output circuit, and a couphng network, said input circuit havlng a variable tuning condenser and a fixed induc-.

tance, said inductance being divided in two parts by an intermediate tap, one of said parts induced voltages from a signal-receiving device and having its terminals connected to said coupling network, said output circuit having a variable tuning condenser and a fixed inductance, said output circuit being coupled to said network and said circuits being tuned to resonance at said desired frequency.

7. An electrical network adapted to select any desired frequency within a predetermined range and simultaneously to reject an undesired frequency which differs from said desired frequency by a constant difference frequency, circuit, an output circuit, and a coupling network including in series a fixed capacity'external pacity included in series with said output circuit, said input circuit having a variable tuning condenser and a fixed inductance divided in two parts by an intermediate tap, one of said two parts being adapted to receiveinduced voltages from,a signal receiving devicev comprlslng'in combination an input' to both of said circuits and a fixed caa variable tuning condenser and a fixed inductance and said circuits'being tuned to resonance at said desired frequency.

8. In a superheterodyne radio receiver means for rejecting the image frequency which comprises a circuit resonant to the signal frequency, a radio responsive device, and means connecting said radio responsive device to said circuit connected to points in said circuit which are at node potential relative to currents of the image frequency.

9. In a superheterodyne receiver means for rejecting the image frequency wh ch comprises an input transformer, including the secondary of said transformer,

means connecting said ra'dio responsive device and sai connection to the said tuned circuit which is at node potential relative to currents of the image frequency.

10. In a superheterodyne radio receiver means or rejecting the undesired image frequency currents which comprise an input transformer, an oscillatory circuit including the secondary of said transformer, a condenser for tuning said circuit, a radio responsive frequency, said points being so selected that.

tuned circuit, said means including a:

a tuned circuit I said tuning means will vary the frequency to which said points are at node potential at the same time that it varies the tuning of the circuit to the desired signal, and the points will be at node potential relative to the image.frequency at any desired point of the tuningra'ngeof said receiver.

11. In a sup-erheterodyne radio receiver means for rejecting the undesired image frequency currents which comprise an input transformer, an oscillatory circuit including the secondary of sa d transformer, a condenser for tuning said circuit, a second oscillatory circuit, a condenser for tuning said second oscillatory circuit and means for coupling a said oscillatory circuits including connections to a portion of the first mentoned oscillatory circuit. which connections are at node potential relative to currents of the image frequency, said points being so selected that the "tuning means of said circuit will vary the frequency to which said connections are at node potential at the same time that t varies the tuning of said circuit to the desired signal, and said points being so selected that the connections will to the image frequency at any desired point of the tuning range of said receiver.

12. In a superheterodyne radio receiver a circuit adapted to suppress the image frequency which comprises a first tuned circuit, a variable condenser for tuning said circuit to cause it to respond to the frequency of the signal current, a second tuned circuit, a variable condenser adapted to tune the second tuned circuit, to respond to the signal frequency, a circuit connecting said tuned circuits connected across a portion of the inductance of the first of said tuned circuits which are at node potential relative to currents of the image frequency and coupled to the second tuned circuit, whereby currents of the image frequency will be attenuated and the currents of said signal frequency will be amplified in the second tuned circuit to compensate for the undesired attenuation of these signals in the first tuned circuit, a radio responsive device and a connection from said second tuned circuit to said radio responsive device connected to a point in the inductance of the second tuned circuit which is at node potential relative to currents of the image frequency, whereby image frequency currents are further attenuated, said tuning condensers being so disposed in each of said tuned circuits that they will s multaneously tune the frequency relative to which the selected points are atnode potential and the frequency to which said circuits are responsive. f

In testimony whereof I affix my signature.

HAROLD A. WHEELER.

be at node potential relative

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