US1944117A - Superheterodyne receiver - Google Patents

Description

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el frfcfm W. S. BARDEN SUPERHETEEODYNE RECEIVER E7I-0JUZMTOH Jan. 16, 1934.

INVENTOR wlw/AM s. EAEDEN ATTORNEY aiented Jan. 16, 1934 Y UNITED STATES PATENT oFFicE 1,944,11r SUPERHETERODYNE RECEIVER William S. Barden, Grasmere, Staten Island, N. Y., assignor to Radio Corporation of America, a corporation of Delaware My present invention relates to superheterodyne receivers, and more particularly to a novel method of, and means for, suppressing undesired responses in radio receivers of the superheterodyne type.

It is well known at the present time that a superheterodyne type of receiver may be embodied in a comparatively low priced chassis and cabinet. Such superheterodyne receivers, often termed midgets or sub-midgets, usually embody a rst detector circuit, intermediate frequency amplifier, a second detector, an audio frequency amplier, reproducer, and a certain amount of radio frequency amplification between the antenna and the rst detector circuit. However, because of the economy requirements in the construction of such low priced receivers, the degree of selectivity between the antenna and the rst detector is not comparable to the relatively higher degree of selectivity in a more expensive superheterodyne receiver. Y

One of the undesirable results of such insulicient radio frequency ahead of the first detector resides in annoying response due to heterodyn- 'A ing between undesired carriers. A particularly disagreeable type of undesired response in a superheterodyne receiver, where economy of construction is the prime consideration, occurs when two undesired carriers are impressed on the antenna circuit which differ by approximately the intermediate frequency. employed. The insuflicient radio frequency selectivity ahead of the `first detector permits these undesired signals to reach the first detector where ythey heterodyne, and thereby cause an intermediate frequency component. The latter component in turn heterodynes with the desired intermediate frequency signal which has been produced by the Aheterodyning of the local oscillation and the desired radio frequency carrier to which the radio frequency system is tuned.

Now, I have discovered a novel method of, and devised means for, suppressing undesired responses in a low priced superheterodyne receiver wherein the undesired responses are caused particularly by undesired carriers differing by` approximately the operating intermediate frequency, and which undesired carriersv cannot be blocked by sufficient radio frequency selectively ahead of the first detector.

Accordingly, it may be stated that it is one pf lthe prime objects of the present invention lto provide a superheterodyne receiver of the `type employing tuned radio frequency amplification ahead of. the first detector and intermediate frequency amplification between the rst and second detectors, wherein the ratio of intermediate frequency gain to radio frequency gainY is maximized to avoid undesired responses due to. heterodyning produced by two undesired carriers differing by approximately the operating intermediate frequency. Y

Another important object of the present invention may be `said to reside in the provision of a superheterodyne receiver, of the type wherein economy of price and construction is the main consideration, the receiver being characterized by the fact that its intermediate frequency amplier gain'bears a predetermined relation to its radio frequency amplifier gain, and this relation is such Vthat undesired response caused by heterodyning of two undesired carriers differing by approximately the operating intermediate frequency is substantially eliminated.

Another object of the present invention is to provide in a superheterodyne receiver, a device for simultaneously decreasing radio frequency amplification prior to the first detector and increasing intermediate frequency amplification between the first and second detectors in a ratio such that there is substantially suppressed undesired responses due to the heterodyning of two undesired carriers differing by approximately the operating intermediate frequency.

Other objects of the present invention areto improve generally the efiiciency of low priced superheterodyne receivers, and to particularly provide a receiver of this type which is not only economically constructed and marketed, but reliable in operation and free from undesired responses.

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 drawings in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawings,

Fig. 1 shows generally a superheterodyne receiver embodying the present invention,

Y Fig. 2 shows a graphical explanation of the present invention,

4Fig. 3 shows aY modified form of the invention,

Fig. 4 shows still another modification,

Fig. 5 shows still another modified form of the invention.

Referring now to the accompanying drawings wherein like reference characters designate similar circuit elements in the different figures, there is shown in Fig. 1 a superheterodyne receiver, which is to be understood as being of the so-called midget type, the receiver embodying the usual grounded antenna circuit A, a radio frequency amplifier having a tunable input, rst detector having a tunable input, a tunable local oscillator, an intermediate frequency amplifier, and a second detector whose output is adapted to be coupled to an audio frequency amplifier and a reproducer. The tuning devices, such as variable tuning condensers, in the radio frequency amplier, rst detector and local oscillator circuits are arranged to be uni-controlled as -shown by the dotted lines 1, in any well known manner. The tunable circuits of the radio frequency amplier and first detector. stages vare tuned to a common signal frequency, and this differs from the local oscillator frequency by the desired operating intermediate frequency. The construction of a superheterodyne receiver of the type shown in Fig. 1 is too well known to those skilled in the art to require any further description.

In low priced superheterodyne receivers it is impossible to provide sufficient radio frequency selectivity ahead of the first detector because of cost considerations. It has been found that a particularly annoying type of undesired response occurs in such a low cost receiver when the antenna circuit picks up two undesired carriers which differ by approximately the operating intermediate frequency. The insufficient radio frequency selectivity ahead of the first detector permits these two undesired signals to reach the first detector. There they heterodyne and produce an intermediate frequency component which heterodynes with the desired intermediate frequency signal which has been produced by the heterodyning of the local oscillation and the desired radio frequency carrier to which the radio frequency amplifier and rst detector are tuned.

Now, it can be shown that the undesired intermediate frequency component due to the two undesired carriers, say A and B, is proportional to the product of the intensities of A and B. If

the gain of the radio frequency amplifier tube is halved, the strength of this undesired intermediate frequency component caused by A and B is quartered. The intermediate frequency ampliiier gain is now doubled in order to maintain the original desired signal sensitivity. It will now be seen that the result of halving the radio tical, until limited by other considerations.

frequency gain and doubling the intermediate frequency amplifier gain is to halve the strength of the undesired intermediate frequency component at the second detector.

Similarly, when the radio frequency amplifier gain is decreased four-fold, and the intermediate frequency amplier is increased four-fold, the undesired intermediate frequency component, due to the product of A and B, is quartered. Therefore, as a fundamental principle in the design of a low cost superheterodyne receiver of the type shown in Fig. 1, there should be employed as low a radio frequency stage gain (grid of radio frequency tube to grid of first detector tube) and as high an intermediate frequency gain (over-all intermediate frequency system including conversion gain of first detector) as feasible, or prac- This has been found very desirable n the efficient 0peration, with minimum undesired response, of low cost superheterodyne receivers. In other words, it will be seen that the essential design principle involves the maximization of the quantity intermediate frequency gain. radio frequency gain In Fig. 2 there is shown charted, in a purely illustrative manner, the eect of the present invention in reducing the operating disadvantage already described. Under the title Original Condition there is shown in Fig. 2 the quantitative relation between the desired intermediate frequency component and the undesired intermediate frequency component whose effect is to be minimized. It will be noted that the desired intermediate frequency component is the product of the desired signal and the local oscillation, while the undesired intermediate frequency component is the product of the undesired carriers A and B. The ratio of desired intermediate frequency component tc undesired intermediate frequency component is 8:1 in the example given in Fig. 2. Of course, the intensity units, and

ance with the present invention. It will be notil;

ed that the desired signal has been reduced to half of its original intensity, and the product, or desired intermediate frequency component is now 16 units. However, each of the undesired carriers A and B have been reduced to one unit in in- "j tensity, and their product is therefore one unit. Hence, it will be seen that the ratio between the desired and undesired intermediate frequency components is now 16:1.

Under the title AMPL. there is shown how the original signal sensitivity is restored by increasing the intermediate frequency amplification. The desired intermediate frequency component is now restored to its original 32 units, while the undesired co.l f '1.

ponent has been only increased to 2 units. Therefore, it will be seen that although the original signal sensitivity has been restored, the ratio of desired to undesired intermediate frequency component is still 16:1. In this way the present invention enables the undesired response due to the heterodyning of the undesired carriers A and B to be substantially suppressed, while the original signal sensitivity is substantially maintained. As has been pointed out heretofore the receiver shown in Fig. 1 may have its radio frequency amplifier and intermediate frequency amplifier originally designed to accomplishthe effects graphically shown in Fig. 2.

In Fig. 3 there is shown a modification of thev present invention wherein a superheterodyne receiver, of the type shown in Fig. l, may include, in addition to the uni-control tuning mechanism 1, and the manual volume control (M. V. C.)

Effect of Increased I. F.

2, a device for suppressing undesired response of radio frequency amplifier tube 4, and a secondy ICH variable resistor device 5 connected between the grid and cathode of the intermediate frequency amplifier tube 6. A uni-control means 7, shown in dotted lines, may be connected in any desired manner to mechanically couple the sliders 8, 9 of the devices 3 and 5 so that when the slider 8 moves in the direction of the arrow, to increase the negative bias of tube 4, the slider 9 moves in the opposite direction to decrease the negative bias on the grid of tube 6.

In this way the effects graphically charted in Fig. 2 may be secured. In other words, the device 7 functions as a manual gain control for the radio frequency and intermediate frequency ampliers, which gain control is independent of the manual volume control device 2 disposed between the output ofthe second detector and the input of the audio frequency amplifier. The number of sliders 8 and 9 may be so arranged that when the gain of the radio frequency amplifier tube 4 is reduced by half then the gain of the tube 6 would be doubled. Of course, the devicev 7 would not be actuated by the operator of the receiver until the type of interference discussed above would make itself manifest. The operation of this form cf the invention is believed to be clear from the description of Fig. 2.

Fig. 4 shows a modification of the arrangement in Fig. 3 wherein a single grounded slider l0 is employed to cooperate with a single resistor l1 to vary the gain of the radio frequency and intermediate frequency amplifier tubes 4 and 6. Only such portions of the circuit are shown in Fig. 4 which are necessary to an understanding of the invention. rThus, the first detector cir cuit is shown in Fig. 4 conventionally as a detector-oscillator stage, the construction of the latter being weil known to those skilled in the art. In Fig. 3, this stage is generally designated as a frequency changer.

The variation in Vgain of the tubes 4 and 6 in Fig. 4 is produced by connecting the resistor ll between the cathodes of tubes 4 and 6, and biasing the control grids of these tubes with respect to the cathodes. Thus, when the tap 16 is moved along the resistor l1 towards the cathode of tube 6, then the negative bias of the grid of tube 4 with respect to its cathode is increased, while the negative bias of the grid of tube 6 is decreased.

The manual volume control in this figure is shown of a different type, and involves the use o f a variable resistor l2 disposed in the screen grid circuit of tube 6. The operation of the arrangement shown in Fig. 4 is similar to that described in connection with Figs. 2 and 3.

In Fig. 5 there is sho-wn still another possible modification of the arrangement shown in Figs. 3 and 4. Here, the amplitude of the radio frequency energy impressed on the detector-oscillator stage is controlled by varying the radio freo the grid of the intermediate frequency amplifier tube 6.

Here, again, when the slider l0 is moved along the resistor 11 towards the cathode of tube 6, the radio frequency signal input to the radio frequeni `cy amplier is reduced, while the intermediate frequency amplifier gain is increased. Hence, it will be seen that the operation of this modification of the invention results in the effects described in connection with Fig. 2. By reducing the amount of radio frequency signal energy collected by the antenna circuit to one half, for example, and simultaneously doubling the intermediate frequency amplifier gain, the ratio of desired intermediate frequency component to undesired intermediate frequency component will be doubled. Of course, as stated in connection with Fig. 3, the slider 10 would not be adjusted until the type of undesired response referred to arises and is reproduced by the reproducen In the modification shown in Figs. 3, 4 and 5 it is to be clearly understood that adjustment of the undesired response suppressor may be made to cover a wide range of conditions. That is, the suppressor device could be adjusted to conform to the intensity of the undesired response. It is believed that the range of movement thereof will be obvious from the aforegoing description, and it is to be clearly understood that this range of adjustment may be as wide as desired, or as small as desired, depending upon the undesired responses sought to be suppressed.

Moreover, while I have indicated and described several systems 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 organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. A method of reducing undesired response in superheterodyne reception, which undesired response is produced by the heterodyning of at least two `undesired carriers differing by substantially the operating intermediate frequency, which consists in collecting the undesired carrier energy and the desired signal energy, reducing the amplication of the said collected energies substantially below a predetermined normal amplification level, impressing the amplified energies upon a 1 .by substantially the operating intermediate frequency, which consists in simultaneously collecting desired signal energy and said undesired carrier energies, amplifying the said collected energies, impressing the amplified collected energies upon a frequency changer to produce a desired intermediate frequency component which is derived from said desired signal frequency energy and an undesired intermediate frequency component which is the product of the said two undesired carrier energies, amplifying the desired and undesired intermediate frequency com-ponents, and simultaneously reducing the said first amplification and increasing the said second ampliiication in a predetermined manner to substantially increase the ratio of said desired component to said undesired component when the intensity of the latter becomes undesirable.

3. In combination, in a superheterodyne receiver,a firstdetectona second detector,aninter mediate frequency amplifier connected between 'the first and second detectors, and a radio frequency amplifier connected to the input of the first detector, the selectivity of the amplifier preceding said first detector being insufficient to prevent the production of undesired intermediate 'frequency component caused by at least two undesired carriers differing by substantially the operating intermediate frequency, and the gain of said radio frequency amplifier being of such a magnitude with respect to the gain of the intermediate frequency amplifier that the ratio of desired intermediate frequency component to the said undesired component is greatly increased.

4. In combination, in a superheterodyne receiver, a first detector, a second detector, an intermediate frequency amplifier connected between the first and second detectors, and a radio frequency amplifier connected to the input of the first detector, the selectivity of the amplifier preceding said first detector being insufficient to prevent the production of undesired intermediate frequency component caused by at least two undesired carriers differing by substantially the operating intermediate frequency, and means for adjusting the gain of said radio frequency amplifier to such a magnitude with respect to the gain of the intermediate frequency amplifier that the ratio of the desired intermediate frequency component to the said undesired component is greatly increased.

5. In combination, in a superheterodyne receiver, a rst detector, a second detector, an intermediate frequency amplifier connected between tlie first and second detectors, and a radio frequency amplifier connected to the input of the first detector, the selectivity of the amplifier preceding said first detector being insufficient to prevent the production of an undesired intermediate frequency component caused by at least two undesired carriers differing by substantially the operating intermediate frequency, and means for decreasing the gain of said radio frequency amplifier to such a magnitude and increasing the gain of the intermediate frequency amplifier to such an extent that the ratio of the desired intermediate frequency component to the said undesired component is greatly increased.

6. In combination, in a superheterodyne receiver, a iirst detector, a second detector, an intermediate frequency amplifier connected between the nrst and second detectors, and a radio frequency amplifier connected to the input of the first detector, the selectivity of the amplier preceding said first detector being insuiiicient to prevent the production of an undesired intermediate frequency component caused by at least two undesired carriers differing by substantially the operating intermediate frequency, and a single means for decreasing the gain of said radio frequency amplifier to such a magnitude and increasing the gain of the intermediate frequency amplifier to such an extent that the ratio of the desired intermediate frequency component to the said undesired component is greatly increased.

7. In a superheterodyne receiver, a frequency changer, means for collecting signal energy of the broadcast frequency range, a selective circuit, including a frequency selection means, coupling said collecting means and said frequency changer, an intermediate frequency amplifier coupled to said frequency changer, the selectivity of said Vselective circuit being insufficient to prevent undesired carriers from reaching the frequency changer and producing a heterodyne frequency which is of a frequency substantially equal to the operating intermediate frequency, and means for simultaneously decreasing the intensity of the desired signal and undesired carrier energies impressed on said frequency changer to a predetermined fraction, and increasing the gain of said intermediate frequency amplifier by a number of times equal to the denominator of said fraction when the intensity of said undesired intermediate frequency component becomes undesirable.

8. In combination, in a superheterodyne receiver, a frequency changer circuit, a second detector circuit, an intermediate frequency amplifier coupling said frequency changer and second detector, a radio frequency transmission network coupled to the input of said frequency changer, and a single means for simultaneously decreasing the transmission efciency of said radio frequency network and increasing the gain of said intermediate frequency amplifier in a predetermined manner with respect to said transmission efficiency reduction.

9. In a superheterodyne receiver, a first detector circuit, a second detector circuit, an intermediate frequency amplifier coupling the first and second detectors, a radio frequency amplifier connected to the input of said first detector, and means for simultaneously decreasing the gain of said radio frequency amplifier and increasing the gain of said intermediate frequency amplifier.

WILLIAM S. BARDEN.

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