US1912059A - Superheterodyne receiver - Google Patents

Description

May 30, 1933- w. s. SARDI-:N

SUPERHETERODYNE RECEIVER Filed June 18. 1931 G imm.

INVENTOR VLLUM S BARDEN hmm ATTORNEY lllll mum Patented May 30, 1933 UNITED STATES PATENT OFFICE WILLIAM S. BARDEN, OF STAPLETON, STATEN ISLAND, NEW YORK, ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE SUPERHETERODYNE RECEIVER Application filed June 18,

My present invention relates to radio receivers, and more particularly to a method of, and means for, reducing interference in the operation of a superheterodyne receiver.

A type of interference that is difficult to eliminate when using a radio receiver comprises an interfering component, or components, falling on one side of a desired carrier, either above or below. For example, assuming that the desired signal carrier is 900 kilocycles, and the modulation com ponents carried in the lower and upper side ands (895 to 905 kilocycles inclusive), then interference components disposed in either the upper or lower side bands are difficult to eliminate. Usually, however, there will exist lesser interference in one of the side bands.

Now, I have discovered a method of, and devised means for, eliminating side band interference by excluding at the radio receiver that side band with the greater interference, and conveniently retaining the side band including the lesser interference.

Accordingly, it is one of the main objects of my present invention to provide a receiving arrangement wherein, at the receiver, the side band including the lesser interference may be conveniently retained, and wherein the remaining side band is excluded, means being provided whereby the interfering component, or components, may be a parently shifted from one side band to t e other side band.

Another important object of the present invention is to provide in a superheterodyne receiver an arrangement for suppressing one of the side bands of the intermediate band of frequencies, and a means for selectively positioning interference components to be eliminated in the suppressed band.

Another object of the present invention is to provide in a superheterodyne receiver including a frequency changing tube, an intermediate frequency amplifier and a second detector, means positioned between the frequency changing tube and the second detector for suppressing one of the side bands of the intermediate frequency band, and local oscillation means adjustable to dispose unde- 1931. Serial No. 545,211.

sired interference frequencies in the side band to be su pressed.

Still other o Jects of the present invention are to improve generally the efficiency of superheterodyne receivers, and to particularly provide a receiver of this type which is free from interference residing in a desired band of signal frequencies.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically one circuit organization whereby my invention may be carried into effect.

In the drawing,

Fig. 1 diagrammatically represents a superheterodyne receiver embodying the present invention,

Fig. 2 is a graphical representation of the problem sought to be solved,

Figs. 3 and 4 graphically represent the shifting of the side band interference,

Fig. 5 shows the characteristic of the side band suppressing means employed in Fig. 1.

Referring to the accompanying drawing in which like characters of reference indicate the same parts in the dierent figures, there is shown in Fig. 2 a graphical representation of an interfering component disposed on one side of the desired carrier frequency. Thus, the full line at 900 kilocycles represents the carrier, while the two remaining shorter full lines, on each side of the carrier line, represent the attendant side bands extending from 895 to 905 kilocycles inclusive, the width of the usual broadcasting band. The interfering component is shown in dotted line, and is situated at 901 kilocycles. Of course, the interference may, also, be located in the lower side band, or even be in both side bands; but, assume the case where the greater interference is situated at 901 kilocycles in the upper side band. In Figs. 3 and 4 there are shown graphically the action of a usual superheterodyne receiver on a desired broadcast band. As is well known, the radio frequency carrier and associated side bands may be lowered in frequency by a frequency changing device, as the first detector tube.

Considering Fig. 1, the antenna circuit A, G impresses the collected energy upon the input of a. tunable radio frequency amplifier. The variable condenser representation is to be understood as the means for tuning one, or more, stages of the amplifier to the desired carrier frequency, 900 kilocycles, in Fig. Q. The local oscillator may be adjusted by'the variable condenser 2 to produce oscillations of a frequency above, or below, the carrier. In either case the first detector produces in its output the difference, or intermediate, frequency to be. amplified and again detected for utilization.

Assume that the intermediate frequency to be employed is 100 kilocycles. then Fig. 3 shows the desired signal carrier positioned at 100 kilocycles while its associated lower and upper side bands extend from 95 to 105 kilocycles inclusive. This. is. also. true in Fig. 1. If the local oscillator is adjusted to produce oscillations at S00 lfilocycles so as to secure the intermediate frequency of 100 kilocycles. it is obvious that the interference component which is located at 901 kilocycles will be situated in the upper side band of the L' intermediate frequency band at 101 kilocycles.

On the other hand, if t-he local oscillator is adjusted to 1000 kilocycles, then the interference component is situated in the lower side band of the intermediate frequency band at 99 ltilocycles. In other words, by adjusting the local oscillator to either of its two possible settings. there is provided a means for shifting an interference component from one side band to another side band, the shift being apparent only in the intermediate frequency band.

Now, by disposing a low pass filter between the first and second detectors. which filter has a characteristic as shown in Fig. 5, it is possible to suppress substantially completely the upper side band of the intermediate frequency band. For example, a low pass filter. possessing the characteristic shown in Fig. 5, may be disposed between the first detector and the intermediate frequency amplifier, and another such filter B may be located between the intermediate frequency amplifier and the second detector. In this way, there may be secured complete suppression of the upper side band. although it is to be understood that for the purposes of the present invention even one of the low pass filters may be used by itself.

It will be seen from Fig. 5 that the characteristic of the low pass filter is such that there is secured a sharp cut-off at the intermediate frequency, namely 100 kilocycles. Clearly with an interference component in the upper side band of the radio frequency band. the local oscillator should be adjusted to operate at 800 kilocycles so that the interference component will remain in the upper side band, and be suppressed when transmitted through the low pass filters A and B. This should be clear from Fig. 4 where there is shown a shifting of the interference component into the lower side band after local oscillations of 1000 kilocycles are employed. Since the lower side band is passed by the low passv filter. obviously the local oscillator, for the situation shown in Fig. 2 should be operated at 800 kilocycles.

On the other hand, if the greater interference existed in the lower side band in Fig. 2, for example at 899 kilocycles, then the local oscillator would be operated at the upper local oscillation, namely 1000 kilocycles, be-

cause in that case the interference component would be shifted into the upper side band at 101 kilocycles whereby it would be suppressed when transmitted through the low pass filter. The same treatment can be applied, of course, to more than one interference component situated in either of the side bands.

Those skilled in the art clearly understand the manner in which a low pass filter having a characteristic shown in Fig. 5 is to be designed. For example, Campbell in United States Patent 1,227,113 issued May 22, 1917. and United States Patent 1,493,600 issued May 13, 19:24 discloses methods for designing such filters.

The sharpness of eut-off is increased by using inductances and capacities in the low pass filter of very low resistance values, and it is again pointed out that the purpose and intent in this invention is that filters with sharp cut-ofi' characteristics shall be employed. lllitliout going into further details as to the specific construction of the filters it is explained that a low pass filter comprises a series of elements consisting of inductances in series and capacities in shunt with each other. the design being such that all frequencies below a certain value (in this case 100 kilocycles) are transmitted, but all frequencies above the critical frequency are suppressed.

Of course. instead of using a low pass filter in the present invention, it is entirely feasible to employ a high pass filter in which case the local oscillator would be so adjusted that an interference component or components, would be shifted into the lower side band to be suppressed. Even a band pass filter may lie employed between the first and second detectors, a similar method of operation being followed in such case.

lVhile I have indicated and described one system for carrying my invention into effect it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, may be made Without departing from the scope of my invention as setforth in t-he appended claims.

`What I claim is:

l. A method of operating a superheterodyne receiver which consists in collecting a signal carrier and associated side bands, one of the side bands including at least onentijference component, simultaneously reducing the carrier andside bands to an intermediate frequency carrier and associated side bands and shifting the interference component to the intermediate frequency side band opposite to its corresponding signal carrier side band, and suppressing the intermediate frequency side band containing the shifted interference component.

2. A superheterodyne receiver, comprising means for collecting a signal carrier and associated side bands, one of which side bands includes at least one undesirable interference component, means for reducing the signal carrier and its side bands to intermediate frequencies, a second frequency reducing means, means disposed between the two frequency reducing means for suppressing the intermediate frequency side band containing the undesirable interference component, and means for shifting the undesirable interference component from its position in the collected band to an opposite position in the intermediate frequency side band which is to be suppressed.

3. A superheterodyne receiver, comprising means for collecting a signal carrier and associated side bands, one of which side bands includes at least one undesirable interference component, means for reducing the signal carrier and its side bands to intermediate frequencies, a second frequency reducing means, means disposed between the two frequency reducing means for suppressing the intermediate frequency side band containing the undesirable interference component, and means including an adjustable local oscillator for shifting the undesirable interference component from its position in the collected band to an opposite position in the intermediate frequency side band which is to be suppressed.

4. A superheterodyne receiver, comprising means for collecting a signal carrier and associated side bands, one of which side bands includes at least one undesirable interference component, means for reducing the signal carrier and its side bands to intermediate frequencies, a second frequency reducing means,means comprising at least one low pass filter disposed between the two frequency reducing means for suppressing the intermediate frequency side band containing the undesirable interference component, and means for shifting the undesirable interference component from its position in the collected band to an opposite position in the intermediate frequency side band which is to be suppressed.

5. A superheterodyne receiver, comprising means for collecting a signal carrier and associated side bands, one of which side bands includes at least one undesirable interference component, means for reducing the signal carrier and its side bands to intermediate frequencies, a second frequency reducing means, means comprising at leastone filter having a sharp cut-off characteristic at the intermediate frequency disposed between the two frequency reducing means for suppressin the intermediate frequency side band containing the undesirable interference component, and means for shifting the undesirable interference component from its position in the collected band to an opposite position in the intermediate frequency side band which is t be suppressed.

6. A superheterodvne receiver, comprising means for collect-ing a signal carrier and associated side bands, one of which side bands includes at least one undesirable interference component, means for reducing the signal carrier and its side bands to intermediate frequencies, a second frequency reducing means, means comprising at least one low pass lter having a sharp cut-off characteristic at the intermediate frequency disposed between the two frequency reducing means for suppressing the intermediate frequency side band containing the undesirable int-erference component, and means for shifting the undesirable interference component from its position in the collected band to an opposite position in the intermediate frequency side band which is to be suppressed.

7. A superheterodyne receiver, comprising means for collecting a signal carrier and associated side bands, one of which side bands includes at least one undesirable interference component, means for reducing the signal carrier and its side bands to intermediate frequencies, a second frequency reducing means, means comprising at least one filter having a sharp cut-off characteristic at the intermediate frequency disposed between the two frequency reducing means for suppressing the intermediate frequency side band containing the undesirable interference component, and means including an adjustable local oscillator for shifting the undesirable interference componentfrom its position in the collected band to an opposite position in the intermediate frequency side band which is to be suppressed.

WILLIAM S. BAR-DEN.

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