US1840064A - Radio telephony receiving apparatus - Google Patents

Description

Jan. 5, 1932. E, D, TlLLYER 1,840,064

RADIO TELEPHONY RECEIVING APPARATUS Original Filed June 26, 1926 g wvento gclgar DTillgen Patented Jan. 5, 1932 UNITED STATES.

'eArE'N'rf 9mm 7 EDGAR n. TILLYER, or soUTHBnIDGE,mssaonnsnrrsnssronon 'ron-Anro conronA- 'IION on AMERICA, on NEW YORK, N. Y., A .oonroaa'rron or DELAWARE RADIO TELEPHONY Rncnrvmo errana'rus.

Application filed June as, 1926, Serial Nb. 118,795. nenewed.;rune 23, 1930.

The present invention relates to radio-telephony receiving sets and has particular reference to an improved receiving apparatus and methods of receiving the radio broadcast waves with the elimination or reductionof obnoxious noises in the reception of these Waves. 7 7

The primary object of the inventionfisto filter the modulated carrier wave of a broadcasting station so that the general interferences accompanying the reception of the said wavemay be greatly reduced orel1m1-- nated.

Another object. of the invention is to provide means ina radio-telephony receivingap paratus whereby the modulated carrier wave of a broadcasting station may be'filtered or tuned with such selectivity as to allow only a small portion of the said carrier wave to passthrough the receivingapparatus, there:

by greatlylreducing or eliminating the general interferences usually accompanying the reception of the said modulated carrier waves. 4 .7 7

Another ob ect ofthe inventlon-ls to provide means in such a receiving apparatus that will filter'the carrier wave along with means whereby the filtered carrier wave may be transformed to the equivalent of the original carrier wave of the broadcasting station so that it will be free from distortion and partially or ahsolutelyfree from the general static, ground and oscillating set interferences when heard by the listener.

Another object of the invention is to provide simple, eflicient andinexpensive means for constructing anapparatus of the character stated.

Other. objects and advantages of the invention shouldbecome apparent by reference to the 'following specification taken in. connection with the accompanying drawings, and

it'will be understood that I may make any modifications in the specific arrangement of been shown and described by way of illustra tion; l

- Present radio-telephony of the best receiving sets for broadcast reception have a certain limit to theirselectivity in tuning, and this limit is due to the width of the audio frequency band it is desired to pass. For

understandable speech' it is necessary to pass I 7 all audio frequenciesup to perhaps 2500 cycles per second and for music up to from 5000 to 6000 cycles, or'perhaps more per second. It, therefore, has been necessary to allow a wide audio frequency band to pass through the receiving set so that music, speech, etc., will be free from distortion when, heard by the listener. As aimea-ns 'ofillustration let us assume that 7%) is the radiofrequency of the carrier wave of a broadcasting station; (fa) the audio frequencyofany note or group of notes desired to be received; (fA) the maximum audio frequency or highest overtone it is desired" to receive,and (FR) the radio frequency added by the first oscillator.

7 i For eXample, a broadcasting station sends these frequencies, which are entirely outside of the tuningrange when a receiving set 1s tuned to the fundamental frequencyor which 1nc y not be transmittedatall, depending entirely onathe transmitting circuit.

'- The present receiving sets, therefore, must tune broad enough to include all of these frequencies, fr plus fa, fr-and f1" minusfa, if no distortionis to be permitted, or with the least possible amount of distortion. This broadnessof tuning is objectionable as it introduces many undesired features, such as the general crashing static interferences, power ground interference, and interference of heterodyning stations, all of which tend to destroy the music or speech being received. Theseinterferences may be reduced or eliminated only by increasing the selectivity of tuning, and previous to the present invention this has not been accomplished except at the expense of eliminating the higher audio frequencies which give character to music, that is, the terms involving fa when this frequency is a high audio overtone.

It, therefore, becomes the most important object of this invention to provide a radiotelephony receiving set which shall be very selective in tuning and which shall filter the broadcasted radio wave so as to reduce or eliminate the interferences accompanying the modulated carrier wave as heretofore stated, and which shall produce undistorted music or speech when heard by the listener.

Before the present invention if the tuning was increased in selectivity until only one band, that is, from (fr to fr plus fa) or (fr to fr minus fa) were passed, that is, just excluding or weakening fr, the result would be that a signal of double audio frequency or 2fa is detected, since when. fr is weakened the detected current has a frequency of 2 fa and fa instead of fa alone.

This, of course, is no longer music or speech, so it is necessary to provide means whereby this distorted double frequency signal may be. changed to the undistorted true representation of the original signal impressed on the original carrier wave.

This special receiver must be so selective in tuning that it will distinguish between f1- minus fA and fr or fr plus fA and fr and then add the necessary fr or its equivalent from a local oscillator so that the audio component fa will be detected as fa and not 2 fa or 2 fa combined with fa.

By these transformations I produce a broadcast receiving set having probably more than twice the selectivity in tuning than that of previous sets of this character, reducing undesired disturbances and greatly increasing selectivity. This increase in selectivity is so great that by proper adjustment of the circuits two heterodyning stations may be separated. This separation is accomplished by tuning on the two side bands which are farthest away from each other. Likewise, the squeals and interferences from regenerating sets are reduced by at least one-half, as they will not be heard unless they are on the side of the station frequency the receiver is tuned to pass. By a slight change in the tuning the other group of frequencies may be tuned in and the squeals thereby eliminated.

We can, as has been done in transatlantic experiments, transmit only fr minus fa or fr plus fa by introducing the proper power amplifier with a saving in power. The receiving system in this instance will detect the frequency as 2 fa instead of fa unless a frequency of is added at the receiver which then detects the frequency as fa. This requires a special transmitter which cannot be received on ordinary receiving sets. However, with the present broadcasting stations which do not eliminate the other two frequencies, and either fr minus fa or fr plus fa, it becomes necessary in order to obtain the advantage of the greatest possible selectivity in tuning to develop a special receiver for the reception of the present type of broadcasting, and it is with this in view and other objects stated above that the present invention is designed so that the advantages which are obtained with special transmitters may be obtained with any standard transmitter and any receiving set.

Referring more particularly to the drawmgs:

Figure 1 shows a diagram of one of the methods in which a receiver of the character stated may be developed.

Figure 2 shows a diagram of another method in which a receiver may be developed.

In Figure 1 the circuit Cl is an ordinary circuit tuned to a band between say f1- and fr plus fa; the other band fr to fr minus fa can be treated in the same way, so it will be only necessary to consider the fr to fr plus fa band. This being an ordinary circuit, it will pass some fr minus fa, these may be somewhat weaker but not greatly so. Circuit C5 is an oscillator giving a frequency of say FR which differs from fr by a low radio frequency. Then there will be an output as in the regular super-heterodyne of a frequency either first fr minus F a minus FR, fr plus fa minus FR and fr minus FR or second FR minus fr plus fa, FR minus fr minus fa and FR minus f1. The prior art circuit of the regular super heterodyne corresponding to C2. C3 and C4 in Figure 1, must tune sufliciently broad to pass all of either the first group or the second group of frequencies previously stated if no distortion is to result. In order to obtain this in the superheterodyne iron core transformer.-;

are often used.

In my combination, however, I make (72. C3 and C4 tune sufficiently selective to exclude completely either first fr minus fa minus FR or, second, FR minus fr plus fa. no matter what values fa may have, always positive however, and also to exclude or greatly weaken either first fr minus FR and fr plus fA minus FR, or second, FR minus fr and FR minus FA minus fr where fA is used to represent the limiting value of fa it is desired to receive. If this is then passed on to the detector in the circuit C4, a distorted audio frequency will be obtained, in general having a frequency of twice the desired audio frequency. I

The circuits C2, C3 and Cat are tuned to maximum response to a frequency midway between either first fr minus FR and fr plus A minus FR, or second, F R minus f1" and FR minus fAminus fr in order to obtain the foregoin result and can be vpermanentlyadj usted to one frequency as the difference between the frequency of the broadcasting station fr to which Cl is tuned and the frequency of the oscillator'FR is tuned so that their difference is constant, soCl and C5 are variable while C2, C3 and C4 are fixed in tun- 1ng.

torted double frequency response corresponding to a real sharply tuned superheterodyne and in order to eliminate or rectify this double frequency distortion C6 is added, premanently tuned to a frequency of either first fr minus FR, or second,FR minus fr, to add the transformed or the equivalent of the eliminated portions of the carrier wave frequency with a frequency that is clear and free from static and other interferences, thereby correcting the detected signal which is a distorted double frequency to an undistorted true representation of the original signal impressed on the original carrier wave. By these transformations we have produced a broadcast receiving set probably more than.

twice as selectively tuned as any previous set, thereby reducingextraneous undesired disturbances and greatly increas ng selectivity.

Other circuits may be utilized to obtain the same filtering actlon or selectivltyin' tuning.

As shown in Figure 2, a regular tuned radio frequency set may be so designed that only the hand between fr and fr minus fA or fa" and fr plus fA is passed, excluding both fr and minus ,fA or fr and f?" plus fA, then adding fr by a variable tuned circuit instead of the fixed one represented in CthFigure 1.

This type of circuit is somewhat more difficult to construct because of the extremely low decrement required when the major frequencies are not separatedto a greater interval beforebeing tuned, as in Figure 1 circuit C5 and also require the copper or metallic casings A for each circuit, as illustrated in Figure 2 to form an extremely selective circuit.

The foregoing hasbeen expressed in terms of mathematical frequencies, but the neces sary data may be. expressed in terms of the carrier wave and the upper sideband fr minus fa, and the lower side band f'zplus As has been previously stated, if only the waves between minus faand f7 orfr plus fa and fr are passed a double frequency distortion will be received, so to overcome this distortion the carrier frequency or its equivalent is added by a local oscillator.

Internal tube element capacities can be As previously stated, this gives a dis":

then reduced or tuned with sufficiently selec,-'

tive circuits to pass only one side band, weakening the upper and lower edges of said hand, then adding the carrier frequency or its equivalent so no double frequency distortion is produced.

Several methods may be used in carrying. I

out the objects of the present invention, such as the' super-heterodyne or shielded .loose coupled circuits, etc., so I do not wish to limit myself to any one circuit. Those shown and described are used simply as a means of illustration:v i

From the foregoing description it will be seen that I haveaaccomplished the objects of theinvention byproviding apparatus that will receive the transmitted modulated carrier wave which comprises the carrier wave itself and both sidebands due to the audio frequency impressed on the carrier Wave by its modulation at the transmitter and will filter out either before, or after changing its frequencies the carrier wave itself and one of the side bands and thenadd a carrier Wave equivalent to the eliminated. carrier waive so that double frequency audio distortion will beeliminatedand thenzp'roviding means for detecting the addedcarrier wave combined with its single side band. I

Having described my invention, I claim: .1." Receiving apparatus for a radio telephony set comprising means for receiving a modulated carrier wave, means for eliminating the carrier wave and one side band, means for generating a local carrier Wave of the same frequency as the original unmodulated carrier wave, and means for combining the other side band with said locally 1 generated carrier. wave.

2.. Receiving apparatus for a radio telephony set comprising avariable circuit to .receive a modulated carrier. wave, a series'of low decrementtuned circuits to eliminate the carrier Wave and one side band, anoscillator to generate a local carrier wave of a frequency equivalent. to the original. carrier wave, and means for combining the other sideband with said local carrier Wave.

3. Themethod of receiving a modulated radio telephony carrier wave comprising eliminatingithe carrier wave and one side band, and adding a carrier-wave frequency equal to the eliminated carrier wave frequency and detecting the new modulated WiLVB;

4. Receiving apparatus for a radio telephony set comprising means for receiving a modulated carrier wave comprising a carrier wave and its associated upper and lower side bands, means to filter out from said modulated carrier wave the carrier wave and one side band, means for adding a new carrier wave equivalent to the one filtered out, and means for detecting the new modulated wave.

5. Receiving apparatus for a radio telephony set comprising means for receiving a modulated carrier wave comprising a carrierwave and its associated upper and lower side bands, means for changing the frequency of the received carrier wave and its side bands, means for filtering out the changed frequency carrier wave and one side band, and means for adding a carrier wave equivalent to the changed frequency carrier wave, and means for detecting the new modulated wave.

6. A method of reception which consists in collecting a modulated carrier wave, suppressing the carrier and one side band, generating local oscillations having a frequency equal to the suppressed carrier frequency, combining the local oscillations with the remaining side band, and detecting the combined local oscillations and side band.

7. A method of reception which consists in collecting a modulated carrier wave, filtering the modulated wave to pass only one side band, generating a wave having a frequency equal to the original carrier wave frequency, combining the generated wave and the aforementioned side band, and detecting the combined band and wave.

8. A method which consists in collecting voice modulated carrier energy, suppressing the carrier and one side band, and combining the remaining side band with locally produced energy of a frequency equal to the suppressed carrier.

9. A method which includes collecting speech modulated carrier energy and suppressing the carrier and one side band, and combining the remaining side band with energy of a frequency equal to the aforementioned carrier frequency.

10. A method of receiving radio telephone waves without undesirable interference, which includes collecting such waves, attenuating the energy of the carrier and one of the side bands of the waves to the point of suppression, combining the remaining side band energy with energy of a frequency equal to the suppressed carrier frequency and free of interference frequencies and detecting the combined energies.

EDGAR D. TILLYER.

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