US1703079A - Superheterodyne radio system - Google Patents

Description

Feb. 19, 1929.

G. L. BEERS surmammonmn RADIO SYSTEM F iled Feb. 18, 1925 Ear 1 1 1T INVENTOR Geagml. Beer:

ATTORNEY %TNESSES: M

Patented" at. 19, 1929.

GEORGE L. BEERS, or WILKINSBURG, 'rENNsvLvAiiIA, 'ASSIGNOB ro WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATIQN'OF PENNSYLVANIA.-

sUPEmTEnoDYnE RADIO. SYSTEM.

Application nled'l'ebruary s, 1925. Serial No. 10,004.

My invention relates to radio receiving-apparatus and particularly to such apparatus as employs the superheterodyne principle;

An object of my invention, is to providea radio receiving apparatus of high selectivit with respect to two frequencies and in whic means are embodied for removingone of the received frequencies. Another object of paratus embodying means for preventing response to a second frequency which may be heterodyned to the beat frequency.

Another object of my invention is to construct a radio-frequency heterodyne radio receiving apparatus having a drain coil thereln.

I Another object. of my invention is to construct a superheterodyne radio receiving system having means for suppressing a second frequency to which the system is responsive.

Another object of my invention is to 0.011- struct a superheterodyne radio receiving system having a singletuning hump.

In the'operation of radio receiving a paratus of the superheterodyne type, it has een found that there are two frequencies which may be simultaneously heterdodyned to give the'same beat frequency. The radio-receptor system may be tuned to a given frequency and "the local oscillator may be adjusted tothe proper frequency to give a beat with the desired signal of a frequency to whichthe associated amplifier apparatus is responsive. Un-

der theseconditions, the system is sensitive and is responsive to'-ver weak signal-energy of the frequency to w ich the receptor is tuned. The rejector properties of the beat frequency amplifiers cause other faint signals" to "be attenuated to such'an extent that they are not perceptible in connected signal translating apparatus. This attenuation is very marked because the radio receptor is tuned .to a single frequency. Therefore, the system is very sensitive and very selective.

As is well known in the art, the superheterodyne radio receiving system. produces at the receiving station a radio-frequency differing fromthe incoming signal frequency and which is-determined by the frequency to which the amplifier apparatus is tuned. The

local oscillator may be set to generate at a frequency either higher or lower by the desired amount than the incoming signals.

If, in the desired application, the. oscillator my invention is to pro-" duce a superheterodyne radio 'recelvmg apis tuned to a frequency which is lowcrthan the same amount to react with the oscillationgenerator frequency to produce the {same beat frequency as the higher freo' ueney=sig5 nals. Under these conditions, the lowerfre i f quency signals will be received through tl beat frequency amplifier apparatus. 1f high power sending apparatus is. in. op-

eration near the receiving appa-ratu's,{ it may force oscillations of low amplitude in the; 7

radio receptor. If these oscillations differ from the frequency of the local oscillator by the same amount that the desired faint sigrials-differ, they will be heterody'nedwto the same frequency, which frequency is received and amplified by the associated apparatus and made audible by the signal translator.

Such interference is very ob'ectionable, and is deceptive because of the act that it-disappears upon the change in the local oscillator frequency and may cause the operator to mistakenly believe that he has received signals from the station which he desires to hear.

My. invention provides means whereby such interfering signals at a different fre quency than the frequencyto which the 're-" ceptor is tuned, and which may be the second 'heterodynefre'quency, are drained out of the system, or by-passed, before they reach the heterodyne oscillator and thereby are prevented from influencing the balance of the system.

Other objectsand structural details of my invention will be apparent from the following description when read in connection with the accompanying drawings, wherein Figure 1 is a diagrammatic. represention of circuits and apparatus embodying a preferred form of my invention; and

Fig. 2'is a diagrammatic representation of circuits and apparatus embodying my invention in a manner in which it is twice applied.

In-the'drawings, a radio-receptor 1,, which may be a loop-antenna, is tuned by a condenser 2 and connected to a triode 3 which amplifies received signals at the received frequency. This amplifier for signals at the incoming frequency is a desirable portion of the invention, but is not an essential part thereof. The amplified output of the repeater triode 3 is transferred by electromagnetic induction through transformer coils 4 and 5. An oscillation generator 6, of any desired form,

PATENT oFF1cE.-,-

has a tuned circuit 7 which is positioned in 5. Energy increments transferred to the coil 5 from the coils 7 and 4 combine to give beat phenomena which are resolved by the triode 8 and its associated circuit into a beat-note, corresponding with, and proportional to, the energy of the original incoming signal. This beat-note, which is modulated in accordance with the original signal, is amplified by an amplifier 9, detected by a detector 11 and translatedinto sound by a telephone receiver 12.

A tuned resonant circuit, consisting of an inductor 1 1 and a condenser 15, is connected across the terminals of the receptor 1 in parallel with the tuning condenser 2. The condenser 15 is adjustable and the inductor and condenser together constitute a series resonant circuit having a very low impedance to the frequency to which it is tuned and a very high impedance to all other frequencies.

The system then operates in the following manner. Signals are received upon receptor.

1, which is tuned by condenser 2 to a chosen frequency. These signals are then impressed upon the triode 3 and amplified thereby. The series-resonant circuit consisting of coil 14 and condenser 15 is tuned to another frequency and, therefore, does not by-pass a perceptible amount of the desired incoming signal-energy from the amplifier 3. The output from the amplifier 3 is then heterodyned, amplified and detected in the usual manner.

In the presence of a powerful nearby station, the operator of the receiving apparatus may have occasion to attempt to receive signals at a frequency which requires the local receiver oscillator to generate oscillation at a frequency which ,will simultaneously heterodyne oscillations of the frequency of the nearby transmitting station to the same beat frequency as the desired signals. Thus the near-by station produces a troublesome interference. Under these conditions, the series resonant circuit is tuned to the frequency of the nearby interfering station, whereupon it by-passes the oscillations in receptor 1 of the undesired frequency from the local sending station and prevents most of their effect upon the triode 3.

Unless the nearby station is extremely close, or of tremendous power, the single bypass circuit Will serve to remove so nearly all of the interfering energy'that only an immaterial amount is conveyedthrough the heterodyne system and amplifier to the receivers.

Under extreme conditions of interference, however, a single drain coil may be insuiiicient and a second drain coil may be provided as shown in Fig. 2, wherein an inductor 16 and a condenser 17 are connected across the terminals of the grid-coil 5 of the beat-resolving detector 8. The addition of the inductor 16 and condenser 17 will remove the most troublesome interference.

If but a single station produces interference, the parallel resonant circuit may be tuned to the frequency of that station and may remain continuously adjusted to that frequency. If, however, a plurality of stations are causing interference, the effect of all may be removed by interconnecting condenser 15 and condenser 2 as shown in Fig. 2 in such way that the frequency of the series resonant circuit is at all times such as to drain ofi" the frequency which is such as to he heterodyned to the same frequency as the desired signal. By employing this mechanical interconnection, there is but one so-called tuning hump in the resonant system and the system as a whole is'responsive to but a single frequency and is not responsive to other frequencies of whatever amplitude.

While I have shown but two embodiments of my invention in the accompanying drawing, it is capable of various other changes and modifications therefrom without departing from the spirit thereof, and it is desired, therefore, that onlysuch limitations shall be placed thereon as are imposed by the prior art or indicated in the appended claims.

I claim as my invention:

1. A signal-responsive system comprising an input circuit including tuning means, an oscillator circuit, a filter circuit including tuning means, means for mechanically coupling said tuning means for simultaneous adjustment to maintain the filter circuit so tuned as to filter out an undesiredfrequency which differs from the frequency of the oscillator circuit by an amount equal to one half the difference between said undesired frequency and the frequency of said input circuit.

2. A radio receiving system comprising means for tuning its input, adjustable means for reducing a desired signal frequency simultaneously with materially dilferent interfering signal frequency to the same lower frequency, variable means for removing the undesired frequency and means common to said first named and said last named means for varying them slmultaneously.

In testimony whereof, l have hereunto suhscribed my name this 14th day of February 1925. k

" GEORGE L. BEERS.

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