US2404333A - Radio receiver - Google Patents

Description

July 16, 1946.

HARRY WHALLEY CHARLES WALTER MILLER ATT ORNEYS Patented July 16, 1946 RADIO REoEIvER Harry Whalley, Darwen, and CharlesV Walter ,Millen Sale, England, assignors .to Metropolitan-Vickers Electrical Company Limited, London, England, a company of `Great Britain Application December 16, 1943, Serial No.

l In England August 8, 1941.

1 claim. (c1. 25o-20) t This invention relates specifically to so-cv'alled f with. thefrequency 'of .the persistence, of vision, the

output or outputs due to any received radio transmissionsA whichmay-v be taking place within the waveband being indicated as resonance or peak components perpendicular to atime base waveband component on the screen of a cathode ray tube the time base component being provided synchronously with the scanning such as by means of a saw-toothtype of oscillation generator. Provision can-be madewhereby any selected one of the `,thus indicated transmissions can be tuned into manually and its modulation listened to or recorded or` otherwise indicated, that is to say, the scanningr of the waveband can be effected solely by hand such as through the turning .of a knob about an associateddial indicating the wavelength. In such a panoramic receiver it has been convenient for the purpose of therapidscanning oithe waveband tofffwobble the'value of certain ltuning components -of the oscillatorsection.

of, vafrequency changer valve in -a superheteros vdynecircuitwhich superheterodyne circuit preferably4 has 4three stages of `frequency changing withcorresponding intermediate frequency circuitsi land ,preferably 5 the ,scanning is `effected by aireactor valveassociated with the second ofthe oscillators through'lan amplifier as described in UnitldStates application Serial No. 503,277, -led September, 21; 1943- Y what heejee .Celledthe Single-Span, tuning principle in domestic and otherfradio receivers has been proposed but has not apparently come into cominercialuse. y

The generaladvantages offthesuperheterodyne receiver over other types are also well known and its use in a panoramic receiver is highly desirable, and when panoramic receivers are required to scan a relativelyvlarge number of wavebands, for instance twenty or thirty, there may be great complexity and expense unless provision is made for reducing the number of preset tuning circuits which have to be changed when the waveband to be scanned is altered. In order that the received signals shall have sufficient amplitude at the first frequency changer to override valve noise in the mixer some signal frequency amplification is generally desirable. It is, however, also desirable kthat image" frequency signals fare removed as far as possible from the wavebands covered by the receiver.

The invention is based on the above considerations which are given in greater detail in the following statement which includes further considerations.

In general a satisfactory panoramic receiver shouldhave a high sensitivity to enablethe maximum number of signals to be observed, b the selectivity should be high to give adequate disn crimination between adjacent signals, consistent with thetuned circuits being kable to respond at the rate of time base sweep and of scanning synchronously therewith, cit is desirable at thesame time thatsecond channel interferenceshould be absent or substantially absent; d the process of scanning should involve the smallest numberoi tuning parameters as possible; and e tuning can be conveniently carried out by electronicrather than mechanical means. Y Regarding a above, this involves high overall gainjwhich isconveniently obtainable by the use of an ,amplier of standard design operated at,

for example, 1.6 Irnc. per second or 465 kc. pe-r second. VThis will also satisfy requirement b above while the consequent use of a superheterodyne circuit simplies the requirement d above but it introduces the difficulty of second. channel interference c above'. As an example, a particular receiver may be quoted which was required to cover afrequency range of fromfifteen to thirty megacyclesper second in thirty consecutive bandseach of five hundred kilocycles per secondwidth; such receiver therefore had to be capable of tuning automatically through five hundred kilocycles per second on each of the bands at a recurrence freguency of the order ofrtwenty-iive per second. To

"achieve this mechanically with normal input circuits Wouid haye involved the use of at least two.-

continuously variable timingdevices such as automatically rotating condensers, as wellgascomplicated band switching means to cover the necessary number of bands. effected electronically such as by means of a reactor valve, the switching would not be simplified; therefore a preliminary frequency changing stage (it is preceded by a signalfrequency ampli-v er) was proposed for converting allsignals to a frequency band of ve hundred kilocycles persecond in Width vso that a single automatically variable oscillator and its associated frequency changer would suflice to produce the panoramic sweeps, irrespective of the band to which the receiver was adjusted.

According to the present invention a panoramic If the tuning Were to be f receiver has at least two and preferably three whilst the first oscillator frequency is high for giving a first intermediate frequency higher than 5 any signal 'frequencyr so that the-"tuned Ycircuitv elements, preferably condensers only, which have to be selectively switched to the fixed element of the receiver for frequency band changing are reduced, namely tothose of the oscillator circuit lY which responds uniformly over the band, in the example 33 .mc.i250 kc./sec. and attenuates outside it.- M. 2l is the second mixer stage suppliedj because the image frequency is so high/that it can easily be filtered out, or is even inherently eliminated. The aperiodic signal frequency amplifier 4 .j does not increase the selectivity and gives only aY small gain, but it has beenfound in the coml5 bination above set forth toV give satisfactory per-- formance in practice and also, due tojits'inability to deal with such high frequencieahelpSJlo. iilterout the image frequencies. The first inter-` mediate frequency amplifier circuit` preferably has a' band-pass characteri'sticrcfv adequate ifrequency width which may be, for example,' five hundred kilocycles per second'so' that the frequency wobbling can be done' at the second os` cillator, thus enabling all bands Vselected to have an equal Width. i

In an example olf panoramic receiverinaccordance withV the invention for a signal Vfre` quency rangeof fifteen' to thirty megacycles in steps of five hundred kilocycles-per second, the

. first oscillator frequency is `from forty-eight to circuits are permissible and yet second 'channel interference is avoided, Whilst the choice of band to be observed is decided'fmerely by the tuning of the first oscillator. The use of )this arrange` ment in conjunction with amain'intermediate 45 Y frequency amplifierV with V its .frequencies i chosen appropriately, enables'adequate selectivity, sensi` tivity and freedom from second channel inter-` ference to be obtained,-inspite of .fthe simple nature of the input circuits and the necessarily wide frequency band passed Yby the fr'stintermediate frequency amplifier.' It is to be under` Vst'oo'd'that wev do' notherein claim per se automatically varying the tuning of the second osY cillator instead of the first, in a panoramic re'-` 55 ceiver, f

' The :accompanying drawing is a block diagramLA indicating a particular panoramic radio receivern in accordance with the presentinvention." f

Starting from the left-hand end of the'diagram 60 the rectangle A. l2.. F. AL represents the desirable 2,404,333 1 ,i :ff ifi;

radio frequency amplifier stage which is aperi-V band of signals beingscanned. y #It' that the scanning is over a band of one-,half 'megacycle I. F. A, I is the first intermediate frequency amplifier, which may include a filter from I,- F. A; l Aand from the second oscillator 0.2

the frequency of which, in the example, is lWob- Y Y bled between thelimits of 34.35 and 34.85 mc./ .'isec. L F. A. 2 is the second intermediate frequency amplifier, sharply tuned to 1.6 mc./sec. M. 3 is'the third mixer stage, supplied from I. F. A. 2 and from the third oscillator 0.3, the frequency of which is 2.065 mc./sec. The mixer M.' 3 feeds to they third intermediate .frequency amplifier I. F. A. 3 tuned to 465 kc./sec., this amplifier feeding to the detector Dwhich is preferably associated with a limiter L in accordance with UnitedV States Application Serial No.' l503,280,7iiled .September- 21, 1943.1y The rectangleB. F. O. Vrepresents the beat frequency oscillatorfwhich may be used for heterodyning a continuous wave signal;

in order to obtain an audible beatnote if desired The output from theV detector goes, on the one hand, to the audio frequency amplifier A. A. su

plying the phones VVlh. or loud speaker or other fed from the timeY base generator represented by In a panoramic receiver, an input radiofrequency amplierstage-aperiodic over the 'range f Aof signals to be received, a first frequency changer stage variable to select a band of frequencies of substantiallyA constant' Width to bescanned p and arranged to convert the selected band to an ine termediatefrequency -higher than that ofthe re'v ceived signal, an intermediate frequency ampli fier, a second frequency changer'stage for 'scan-A ning the band selectedv byY the'rst frequency changer stage', means for varying the oscillator frequency of said secpndfrequency changer stage to Veffect panoramic scanning,` and adetector stage forthescannedsignalsl'r j;

HARRY

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