US2381940A - Method and apparatus for simultaneous aural and panoramic radio reception - Google Patents

Description

M. WALLACE EVAL Aug. 14, 1945. 2,331,940

METHOD AND APPARATUS FOR SIMULTANEOUS AURAL AND PANORAMIC RADIO' RECEPTION f Filed July 17 1941 6 Sheets-Sheet 1 Aug' 14' 1945" M. WALLACE ET Al.

METHOD AND APPARATUS FOR SIMULTANEOUS AURAL AND PANORAMIC RADIO REcEPToN Filed July 17 1941 6 SheetS-Sheet 2 QNEESQQ IN VEN TORS` JQQBT y f N 1 0 w WM v n a i@ am Wm 9 OMS ad ma 9%. YI e Aus-14,1945 MWALLA'CE Em 2,381,940

METHOD AND APPARATUS FOR SIMULTANEOUS AURAL AND PANORAMIC RADIO RECEPTION Filed July 17, 1941 6 Sheets-Sheet 5 if@ f5 62 7/ f L 6*/ 1F: can.. E C da da 63a 551 70 54 INVENTORS @nieuwe/e gif/Mace?) o/zace/ SJ/fav,

Aug- 14, 1945- M. WALLACE ET AL 2,381,940

METHOD AND APPARATUS FOR SIMULTANEOUS AUHAL AND PANORAMIC RADIO RECEPTION Filed July 17 1941 6 Sheets-Sheet 4 Aug' 14 1945' M. yWALLACE ET A1.

2,381,940 AURAL METHOD AND APPARATUS FOR SIMULTANEOUS AND PANORAMIC RADIO RECEPTION Filed July 17 1941 6 Sheets-Sheet 5 HIW @WARN SN@ DK IN VEN TORS M N c M mm@ .az www me t naamw 1h 8AM 90,.,6 2e m MS Dun 6 Aug' 14 1945' M. WALLACE ETAL METHOD AND APPARATUS FOR AND PANORAMIC RADIO RECEPTION Filed July 17, 1941 INVENTORS n. M W m Q. W MU ma Patented Aug. 14, 1945 METHOD AND APPARATUS FOR SIMIUL- TAN EOUS AURAL AND PANORAMIC RADIO RECEPTION Marcel Wallace, New York, N. Y., and Horace G.

Miller, Belleville, N. J., assignors, by mesne assignments, to said Wallace, doing business as Panoramic Laboratories, New York, N. Y.

Application July 17, 1941, Serial No. 402,822

20 Claims.

Our invention relates to improvements in methods of panoramic reception and to methods of simultaneous aural and panoramic reception.

One of the objects of our invention is to provide greater facility for manually tuning a panoramic radio receiver over wide frequency ranges, while maintaining a substantially constant visual bandwidth.

Another object of our invention is to provide means for effecting aural reception over a narrow band of frequencies and simultaneous panoramic reception of a wider portion of the spectrum.

Still another object of our invention is to provide, in combination with an ordinary'radio receiver, means for panoramically receiving a wide portion of the frequency spectrum, including that portion over which the ordinary radio receiver is tuned, without affecting the aural reception through that receiver.

Another object of this invention is to provide a panoramic receiver having variable visual bandwidths and variable resolution.

Other and further objects of our invention reside in the various arrangements of panoramic receiving systems described more fully in the specification hereinafter following, by reference to the accompanying drawings, in which: Figure 1 represents a block diagram of a combination of tunable channel which is common to an aural channel and a visual panoramic channel; Fig. 2 represents the response curve of various circuits employed in the receiving system of our invention; Figs. 3a, b, c, represent the screen of a panoramic receiver for three positions of the controls of the tunable channel; Fig. 4 represents the shape of deflections on a screen with various frequency sweep velocities; Fig. 5 represents the type of voltage sweep required for variable resolution reception; Fig. 6 represents a schematic diagram of a panoramic channel, adapted to an ordinary super-heterodyne radio receiver; Fig. 7 represents a schematic diagram of a wide band panoramic radio receiver; Figs. 8a, b, c, represent various views of a synchronous vibrating condenser; Fig. 9 represents a diagram of a radio receiver using such a synchronous vibrating condenser; and Fig. 10 is a block diagram of a multi-channel receiver embodying our invention.

In the copending patent applications of Marcel Wallace, Serial Number 196,520, filed March 17, 1938, now Patent 2,279,151, granted April 7, 1942, for Panoramic radio receiving system, and Serial Number 204,470, filed April 26, 1938, now Patent 2,273,914, granted February 24, 1942, for Radio (Cl. Z50- 20) l0 element connected in the same tuning circuits,

for manually tuning the receiver over the desired portion of the frequency spectrum.

For a further and better understanding of the nature and applications of our invention, reference is made to the copending patent applications of Marcel Wallace, Serial No. 330,763, filed April 20,1940, now Patent No. 2,312,203, for radio beacon and panoramic reception system, and Serial No. 357,814, filed September 21, 1940, for Radio altimeter and panoramic reception system.

For example,` in the case of Fig. l of Marcel Wallaces copending patent application 196,520, (Patent 2,279,151)V supra, the condensers 3 and 4 are periodically tunedand condensers I and 2 are manually tuned. Such an arrangement presents the disadvantage that the frequency sweep is not constant over the entire manually tunable range. When the condensers I, 2 are open, the frequency sweep on the visual bandwidth produced .caused by the rotation of 3, 4 is greater than when the condensers are closed.

In fact, this visual bandwidth decreases proportionally to the cube ratio of the mean frequency of the oscillator. For example, if the mean frequency of the oscillator is F1 with the condenser 2 open and F2 with the condenser 2 closed, the ratio between the two respective visual bandwidths W1 and W2 will be WT F2 In other words, the signals will spread apart on the screen as the condenser is closed. This 5 is not desirable when it is necessary to use a fixed frequency calibration over the screen of the receiver, which should permit instantaneous determination of frequency difference over wide tuning ranges.

Considerable improvements of the panoramic one of these oscillators, and periodic tuning to the other. irrespective of the sequence in which this is done.

Fig. 1 shows in the form of a block diagram. one example of the principles-used in such a double conversion panoramic receiver.V This block diagram is divided into three parts surrounded by dotted lines, representing three channels which are marked respectively: Tunable channel, Aural channel and Panoramic channel. The various elements are shown connected. forming a complete. simultaneous, aural and panoramic receiving system. It must be understood, however, that these various channels can be combined two by two or can be used singly, for definite uses, as more fully explained hereinafter.

The Tunable channel comprises:

A signal input circuit which may include an R. F. amplifier containing one or several stages, a nrst mixer receiving lsignals from said signal input circuit and a nrst oscillator feeding signals into said mixer. The oscillator, or any other of these three elements may be tuned eithersingly or by means of ganged variable condensers, or other type of tuner.

The Aural channel which is coupled to the output of the nrst mixer comprises an. ordinary, sharply tuned, intermediate frequency amplifier tuned to frequency F1, a detector and audio frequency amplifier and an aural responsive device, such as the telephone receivers shown. It will be shown that this aural channel need not be tuned to exactly Fi, but to any frequency within a band extending equally on each side of F1 and that a tuning control in .the said aural channel has certain important applications.

'Ihe Panoramic channel" which is also coupled in the output of the first mixer, is in effect a panoramic receiver, frequency band psig*- Such a panoramic receiver may -be constituted by a single amplifying stage periodically tuned, as shown yin the Marcel Wallace Patent 2,279,151, either by electronic means (Fig. 4) or by mechanical means (Fig. 14) or it may be constituted of a series of cascaded amplifying stages, similarly periodically tuned, or by a complete Superheterodyne circuit such as shown on Fig. 1 of Patent 2,279,151 or Fig. 4 of Patent 2,312,203. Such a. super-heterodyne type of Panoramic channel comprises a second mixer stage which, in the example chosen, is tuned to pass a .band of frequencies of W cycles, but which is centered at the frequency of the aural intermediate frequency ampliiier. (It will be shown that this need not necessarily lbe centered and that a tuning control in the output oi' this panoramic channel has certain applications). In other words, this second mixer will pass a band of frequencies between f l (rz-3g) and (A+-Y2K) 'I'he relationship between frequency and ampliilcation in this Panoramic channelis explained with the aid of Fig. 2: In order to compensate for the sharpness of the response over a band of W cycles, as shown by curve a, due to the selectivity of the radio frequency stages in the Tunable channel, the coupling transformers used in the second mixer are made to increase the amperiodically tunable over a.

pliflcation on the extreme ends of the band and to attenuate the center; this is shown by curve b. Compensation can be obtained in this manner and the resultant over-all amplification can be made to be substantially constant for a given frequency range through the entire band W as shown by curve c.

Separate controls can be used in the coupling transformers to modify the shape of curve b to suit any desirable condition, according to the variations of the selectivity curve a for various ranges of the frequency spectrum.

The signals from a second oscillator are fed into the second mixer. 'I'his oscillator is automatically and periodically tuned over apredetermined frequency band W cycles wide, between W W Foand Fri- (in which Fo represents a fixed mean frequency). 'I'he signals resulting in the output of the second mixer, which can be either the sum or the difference between the signals fed therein, are fed into a second intermediate frequency amplifier having one or several stages. tuned to either this sum or difference. This ampliner (2nd I. F. Amp.) is sharply tuned and has a narrow pass band characteristic. A series of periodic impulses will result in its output, corresponding to the signals present over the band covered by the second mixer stage. These impulses are rectified and amplified in one or several amplifier stages (Det. amp.) and the resulting impulses are applied to one set of deflecting plates of a cathode ray oscillograph.

The second oscillator is periodically hined over a desired range, by means of a periodically varying frequency controlling element, marked Freq. contro which may be a tube, an inductance, a condenser, etc., winch, in its turn, is submitted to a periodic variation by means of a voltage sweep source. This may consist of a motor and/or a source oi' periodically varying voltage. A sweep voltage synchronized with the frequency sweep of the second oscillator is amplified, if desired, and then applied to another set of deecting plates in the oscillograph tube.

It can be readily seen that the mere combination of the Tunable channel" and the "Aural channel" described above, constitutes an ordinary super-heterodyne radio receiver. The "Panoramic channel in itself represents then a complete device which can be connected to such an ordinary radio receiver in the output of its first mixer and constitutes a valuable attachment or adapter to such a receiver.

As the receiver is manually tuned through its tuning range, and while the operator listens briefly to each station in turn. a band of a constant width of W cycles passes in view and all the other signals present within that band appear on the screen of the cathode ray tube as individual inverted V deflections of various amplitudes determined by their respective signal strength. The linear intervals between deections can be made directly proportional to their frequency separation and this relationship is maintained throughout the tuning range of the receiver, which is a very important advantage.

A vertical reference line across the center of the screen corresponds to the frequency to which the receiver is tuned. Amplitudes are measured on this line. A horizontal line across the screen serves as the frequency reference. It can be calibrated in kilocycles (positively and negapassing tively) on both sides of the vertical line corresponding to W/2 kilocycles above and below the frequency to which the Tunable channel is tuned. A zone limited by two parallel vertical lines on each side of the vertical center line, indicates the Aural zone, or the audible range usually covered by the receiver. All deflections through this zone on the screen are heard in the loud speaker or phones of the receiver.

This is illustrated in Figs. 3a, b, c. Fig. 3a shows signal A in the aural zone. Signal B, C, D, E are higher in frequency, whereas F, G, H, J are lower. The frequency of each signal can be determined by algebraically adding to the dial reading of the receiver the number of kilocycles read on the screen, below its corresponding peak. Fig. 3b shows the receiver tuned a few kilocycles higher. Signal C has entered the aural zone. New signals K and L are visible, whereas signals G and H are out of the visual range of the new band covered.

Fig. 3c shows the same screen after tuning the receiver again higher in frequency. The two signals D and E which intersect at the base, but which can still be visually resolved, are both within the aural range, and, therefore, are heard in the receiver with a sharp heterodyne whistle. C. W. signals only a few kilocycles apart can be separated visually, even if those signals cannot be separated aurally, as it will be shown further below.

A panoramic adapter such as described hereinbefore, is limited generally to a visual bandwidth which cannot exceed greatly the passband characteristics of the manually tunable channel. This varies according to the type of receiver, the number and type of R. F. stages and the frequency of operation. Most receivers will have a wider passband at high frequencies than at lower frequencies.

The adapter can have. means for varying the bandwidth W, either continuously or discontinuously, as it has been shown in previous applications. The electronic methods of sweep lend themselves most readily to these variations.

Frequency resolution- As the visual bandwidth of a panoramic receiver is increased, or decreased, the deflections on the screen of the receiver respectively become narrower or wider. The selectivity, or frequency resolution, of those deflections will also vary. Generally a wide band panoramic receiver has less frequency resolution than a narrow band receiver, and while the first one permits a more rapid check up of wide regions of the frequency spectrum, the second one permits more accurate check up when the stations are quite close to each other.

The resolution of a panoramic receiver is determined by the shape of the deflections produced by each signal and the linear separation between those deflections.

While the separation is a function of frequency distribution on the screen, the shape of each deflection'is dependent upon two factors: a static and a dynamic factor. The static factor is the selectivity p (in cycles) of the intermediate frequency and video channels, when the visual bandwidth is reduced to a minimum. In our numerical examples and claims which follow we define the static resolution p of a panoramic receiver as the passband of the filters following the periodically tuned receiving circuit, represented as the difference of frequency, read on the frequency sweep axis, of a panoramic receiver sweeping a frequency bandwidth of very low value, said difference of frequency being read between two points on the deflection produced by a single signal, points, which are at 70% of the maximum amplitude H of that deflection.

The dynamic factor r is also measured in cycles and is a function of "frequency velocity (V) which is defined by the value:

A F At in which: AF is the variation of instantaneous frequency of the frequency swept oscillator in a time At. If the variation of frequency with respect to time is constant, (such as it happens in an electronically controlled system, with a sawtooth sweep) then V is also a constant. By making At equal to unit (one second) the velocity V can be expressed as: the number of cycles of sweep during one second.

By continuously increasing the frequency velocity in a panoramic receiver, the deflection produced by each signal becomes of a lower amplitude and has a tendency to spread in the direction toward which the band is swept.

This is due to the fact that a certaintime is required for signals either to build up or to die out. If the sweep velocity is too great, the signal has no time to build up to lthe same amplitude as it would build by sweeping very slowly; on the other hand the circuits which have built up a signal still retain signals after the cathode ray spot has moved away, on regions corresponding to other frequencies; this is why the signal spreads out.

This is better understood by referring to Fig. 4. A panoramic receiver (or adapter) is periodically tuned from Fo to Fx cycles and the cathode ray spot on the screen moves in the direction of the arrow in synchronism with the periodic tuning. Curve a. shows the shape of the deflection as the receiver is tuned through a signal at a velocity V which should permit a dynami-c resolution r very nearly equal to p, the static resolution of the receiver. As the velocity V is gradually increased, the shape of the curve changes. While the spot rises following the same curve as before, it rises to a lower amplitude and then drops, trailing off further away along the frequency sweep axis. Curve b shows a condition where the value of p is only a small fraction of r. Curve c shows a condition where this condition is further exaggerated. The deflections spread along the screen, one deflection merging into another and the visual `discrimination between stations becomes impossible. When the deflections take such shape, the usefulness of a panoramic receiver is greatly decreased.

From these curves, there can be derived a convenient definition for the frequency resolution of a panoramic receiver, having a frequency sweep of a bandwidth w, a definition to which we will refer in our claims. The frequency resolution S is the difference of frequency, read on the calibrated frequency sweep axis of a panoramic receiver sweeping a frequency bandwidth of w cycles, between two points on the deflection produced by a single signal, which are at '70% of the maximum amplitude H of that deflection. This resolution is represented on Fig. 4 in dotted lines for each curve a, b and c, as Se, Sb, and Se. which are drawn at 70% of the respective maximum amplitudes Ha, Hb, and Hc. The resolution S measured in cycles represents the square root of the sum of two factors: the square of the static resolution p defined above, and the square of the dynamic resolution r. ,The latter varies proportionally to the frequency velocity V.

It can be seen from this that the resolution improves (S decreases) as V decreases, but can never be better than the static resolution P. This static resolution, however, is also tied up to the dynamic rsolution r, as it will be shown below. If the selectivity of the circuits is too great, the signals do not build up to a suillcient amplitude and the receiver will not operate properly.

Practical tests show that the value of K, for the above definition of S is very nearly equal to 2. In other words, 1=\/2 l and s=\/p2+2v (2) The shape of the deflections is generally quite satisfactory provided .that the static resolution p is not smaller than about V5 of the r corre- -1 spending to the highest velocity V required:

On the other hand, the velocity V can be expressed (when V is constant) as V==Wf (4) in which W vrepresents the visual bandwidth covered in one cycle of sweep and f the number of cycles of sweep per second (sweep rate).

Therefore,

S=\/F+2wf (5) The maximum value of W determines the value:

in the condenser C will be disturbed.

If the frequency sweep of that same receiver is reduced to 1 mc. (10 cycles) the resolution S=1l.8 kc. At 100 kc. bandwidth, S=5.60 kc.

The resolution has improved considerably as the visual bandwith wasreduced, but it never can exceed the static resolution 4.4 kc. which was determined by the Wm required.

If the panoramic receiver, however, were designed to cover only 100,000 cycles maximum bandwidth, ory less, p could be only 692 cycles. 'I'he total resolution S of the receiver in this case would be 3.50 kc. at 100 kc. visual bandwidth and only 2.53 kc. at kc. bandwidth.

When a panoramic adapter for an ordinary broadcast band super-heterodyne receiver is to be designed, it is possible to cover a bandwith of about 100 kc. or thereabouts. Such adapters can be designed to give the relatively high resolutions indicated above. 'I'he maximum bandwidth is a function of the intermediate frequency of the receiver and of the amount of preselection of the receiver used.

From Fig. 1, it can be seen, however, that the Tunable channel and the "'Panoramic channel, combined constitute a complete doubleconversion panoramic receiver, in which the visual bandwidth W is not dependent upon the manual tuning adjustment. A

Such a receiver can be designed to cover any desired portion of the frequency spectrum, with the limitations of resolution explained above.

In wide band monitoring systems. it is therefore advantageous to use several such wide band panoramic receivers to cover "roughly" the whole desired portion of the frequency spectrum, and a plurality of narrower band, high resolution, combined aural-panoramic receivers for inspecting the regions where stations are indicated by the V,wide band receivers.

The combination of two screens, one for wide band, low resolution and the other for narrow band, high resolution, is very practical for accurate monitoring of the spectrum. One single tunable channel as shown on Fig. 1, followed by an Aural channel" can feed signals into two parallel visual channels: one of high resolution and the other of low resolution. One screen may cover, for example, a two megacycle band with a resolution o1' 20 kc. and the second screen a band of 100 kc., that is 5% of the first screen. with a resolution of 4 kc. What may appear as a single signal in the flrst screen may be resolved into a number of separate signals in the second one.

With the use of variable selectivity I. F. transformers in the 2nd I. F. amplifier, it is possible to design a more lflexible apparatus. adaptable for any type of service.

For wide visual bandwidth. the equipment as above described may be designed with a special wide-band R. F. amplifying system in the manual tuned channel of Fig. 1. This R. F. system may comprise wide bandpass filters tuned by the manual tuning control, and proportioned so as to have a fiat-topped amplitude-versus-frequency characteristic. In this case the panoramic channel of Fig. 1 may also be provided with yan input bandpass I. F. amplifier having a flat-topped characteristic, to cooperate properly with the manually tuned bandpass channel. e

it has beenv shown, the resolution of -a panoramic receiver is afunction of the frequency sweep velocity. By varying this velocity during each cycle ofsweep, it is possible to vary the resolution over various portions of the visual bandwidth shown on the screen. In an electronically controlled panoramic retions will remain unchanged,l provided that the same waveform is applied to both frequency controlling element in the receiver and to one set of deflecting elements of the cathode ray tube. One type of waveform which will produce a higher resolution in the center of the screen than on the sides is illustrated in Fig. 5, wherein curve a shows a few cycles of sawtooth voltage plotted versus time. Curve b shdws a few cycles of sine wave synchronized in phase with the voltage shown in a. Curve c shows the-voltage resulting by adding the two voltages shown in a and b. It can be seen that the resultant voltage rises first steeply, then much slower and then. toward the end of the cycle it rises again steeply.

' ordinary super-heterodyne radio receiver.

` transformer,

4the sawtooth and the sine wave. it is possible to obtain any desired variation in the frequency velocity. If the velocity is slowed down to zero in the center of each cycle, this velocity is doubled at the extremities. The resolution S will, therefore, be at the center equal to the static component p whereas at 'the extremities Will be S=\/P+4V. Such a distribution of signals has the advantage that the signals which are under closest scrutiny appear clearest and most accurate. This result isobtained simply by inserting into the output of the square-wave generator a sine wa-ve circuit which may be taken from the source of power for the receiver. A phase adjusting bridge is generally required to bring the sawtooth and the sine wave in zero phase relationship.

Fig. 6 shows al schematic diagram of an electronically controlled panoramic channel as shown in Fig. -l, and the electrical connections required to make it operate in cooperation with an An antenna I is shown connected to the conventional super-heterodyne receiver 2, comprising a tunable channel and an aural channel. A mixer tube 3, an aural I. F. transformer 4 and an intermediate frequency amplifying tube 5 are shown. The bandpass input transformer 9-I0 of the panoramic' channel is connected to the plate of the tube 3 through a condenser 6 and a resistor 1. The signals from the mixer tube 3 are fed into a bandpass amplifying tube Il of the panoramic channel through a transformer Whose coupling between primary 9 and secondary l0 is pre-adjusted or is adjustable to give it the desired bandpass characteristic line. This amplifier tube I I is not needed and the signals can be fed directly into the second mixer tube I8. Its presence, however, allows greater peak to peak amplitude ratios of compensation such as shown on Fig. 2, for wider bandwidths to be analyzed. The output of the tube II is fed into a similar type of I4-I5. Both transformers are tuned to the desired frequency by means of variable condensers |2-I3 and l6-l1 respectively. If it is desired to keep the aural band of the receiver fixed in the center of the cathode ray screen, the mid-channel frequency of these transformers must be made the same as that of transformers 4 in the receiver. However, for some purposes it may be desired to shift the aural channel over another region of the screen, or to change the shape of the radio frequency response of the adapter. The condensers |2--I3 and I6-I1 and/or the coupling of the transformers can then be brought on the front panel of the adapter foi` the desired adjustment.

The. signals fromtransformer I 4-I5 are fed into the mixer tube i8 together With the signals from the oscillator 21. The frequency of this oscillator is periodically varied, preferably equally on each side of a mean frequency F0, over a total width of W cycles (from 'I'his frequency sweep is obtained by means of a frequency controlling tube 28 and a proper phaseshifting network 29, 30. The frequency sweep rate (number of frequency sweeps per second) is determined by the frequency of a sawtooth voltage, generated by the tube 3B after coupling yto the tube 31. This voltage is applied to the grid of the frequency controlling tube 28 through the potentiometer 35 from the low impedance cathode of tube 31. The amount of frequency sweep (determining W) is adjustable by means of this potentiometer. The value of the mean frequency Fo is determined by the adjustment of condenser 59. The sharp intermediate frequency amplifier following the second mixer is constituted of input transformer l3-20, amplifying tube 23 and the output transformer 24-25. The detector and amplifier is constituted of diode-triode tube 25.

\ Pulse automatic amplitude control.-In certain of panoramic receivers it is necessary to types signals differing in simultaneously compare strength over wide ranges. Due to the dimensional limitations of a screen, if linear amplification is used, this could not be possible; for example, on a screen permitting a. maximum deilection of 2 inches and on which the smallest distinguishable signal is of 0.1 inch, it is possible to compare only signals having a 20:1 ratio.

By using ordinary automatic volume control systems, having a long time constant, the strongest signal will generally determine the sensitivity of the receiver so that weak signals will not appear in the presence of strong ones. This condition is desirable for certain types of applications but it is not desirable in intercept or monitOring work.

A new improved system of automatic volume control described as pulse A. V. C. is shown on Fig. 6. Instead of applying the D. C. potential, obtained from the rectification of the carrier voltages to the grids of the amplifying tubes, we apply the rapid A. C. pulses created during the sweeping through the various signals, to those amplifying tubes, therefore, obtaining instantaneous variations of sensitivity corresponding to the signal strength of each signal. Tube 39 is coupled through condenser 32 to the output of the 'detector 26 and a potentiometer 40, in its cathode is used to obtain the desired amount of pulse A. V. C. voltage, which is applied to control the bias oi amplifying tubes Il and 23. The stronger the pulse, the greater the control and the amplitude of the deflections will vary in a logarithmic ratio on the screen, permitting comparison of signals having a ratio of 200: 1 or more. The purpose of the coupling tube 39 is to obtain the right polarity for the controlling voltages required.

A manual gain control is provided by means of potentiometer 4I controlling the cathode returns of those same amplifying tubes. The output of the tube 26is D. C. coupled to deecting element 42 of a cathode ray oscillograph tube through potentiometer 52. This D. C. coupling is preferable to an A. C. coupling (through condensers) because the frequency sweep axis remains quite steady and unaffected by variations of amplitude of the signals received; The same results can be obtained by inserting between the output of tube 26 and the deflecting plate 42 one or several stages of D.'C. coupled amplifiers. The output of sawtooth amplifier 31 is connected to deilecting element 43, which is normal to 42, through potentiometer 42', which permits adjustment of the length of the line on the screen.

The above instrument is, as said above, limited to a visual bandwidth corresponding to a certain extent to the pre-selection characteristics of the cooperating receiver.

Fig. 'l shows a schematic diagram of a complete panoramic receiver having a wide visual bandwidth, incorporating a manually tunable power in channel, a panoramic channel and an aural channel. Each of these channels is surrounded by dotted lines. The tunable channel includes ganged condensers 45-46-41. The condensers M are tuning a band-pass transformer including coils 54-55 and an adjustable coupling vconnected to the output of mixer tube I, just as the visual channel was connected in Fig. 8. It must be noted that several such aural channels can be connected in parallel. By tuning their respective transformers 4 and 50 of each channel to slightly different frequencies, various portions of the visual band will through those channels.

By ganging the condensers tuning these transformers, it is possible to listen at will to any signal visible on the screen, without touching the tunable channel ( condensers 45, 46, Il). Instead give aural responses of ganging the condensers, a third converting' stage can be used, and in this caseonly an oscillator requires tuning.

lThese schematic diagrams have been given only as speciilc examples of manners of obtaining the desired results, being quite natural that the results desired can be obtained by many modifications of those diagrams.

Instead of electronic frequency sweep, mechanical sweep can just as well be used, such as rotating condensers, inductances, or other methods such as described more in detail in previous patent applications.

One practical way of obtaining a frequency sweep in step with a source of alternating voltage. is by means of a special synchronous vibrating condenser.

Figs. 8a b, show the construction of such a vibrocondenser. Alternating current is fed into the exciting coil 80 through leads 66, 61. A soft iron core or a permanent steel magnet 69 inserted in this coil creates an alternating magnetic field at its ends. A vibrating steel reed 6| is placed in this field. This will vibrate in step with the magnetic forces produced and will be attracted and repulsed in synchronism. By using a soft iron core, the number of vibrations will be equal to double the frequency of the.l voltage applied. whereas by using a permanent magnet core the magnetic eld is neutralized during half of the time. and the number of vibrations is equal to the frequency of the alternating current. The

reed il is fastened in the` base of S4 of the instrument by means of block 1i, and on the free end one or more parallel condenser plates 62a, b, c. are mounted normally to its surface. These constitute the moving armature of a capacitor. The other armature is fixed and consists of stator plates 63a. b, c, d, which are insulated by means of insulating block 65. 'Ihe dimensions and weight of the reed and moving armature are so proportioned that its natural period of resonance is very nearly that at which it is made to vibrate. 'I'his reduces the required amount* of exciting the coil 60. This period is adjustable by means of a screw 68 mounted on the extreme end of the reed, which varies slightly its eiective length. We iind it ,advantageous to slightly dampen the vibrating reed by, for example. inaerting a sheet of rubber 1I. between the base I4 and block 1I. While this arrangement requires a little more driving power, the amplitude and phase relationship with the driving A. C. voltage remain more nearly constant even .if the frequency of the A. C. varies noticeably.

. Fig. 8a shows in full lines the reed in stationary position corresponding to capacity C0, and in dotted lines fthe reed in extreme vibrating positions, corresponding to capacities Cm and Cmm. It can be seen that it is possible to make this variation equal in each direction (Umax-CoCo-Cinin) or to give, according to the shape of the plates, any desirable variation of capacity versus amplitude of vibration. Such a condenser will vary in step with the A. C. voltage applied. In case of a sine wave, its instantaneous velocity will also vary according to'a lowest, passing through zero, correspondingto capacities is the highest in the central ing to capacity Co. This maximum velocity Vmx=1rV. in which V is the average velocity, corresponding to the frequency of the sine wave.

Figs. 8b and 8c show respectively an end view and top view of the alternating condenser.

Such a condenser can be used to replace the condenser 59 in Figs. 6 and 7. In this case, there is no need of the reactance tube 28. The design can be still further simplined by eliminating the sawtooth generator- 38 and ampliiler 31. The horizontal deflecting element 43 of the cathode ray oscillograph can bethen energized directly with the A. C. current from the same source which energized the synchronous vibrating condenser, as it will be shown on Fig. 9.

Due to the fact that the motion of the con denser is reciprocating, it is sometimes diillcult to make the capacity variations in both strokes absolutely equal. In other words, there may exist a variable phase difference between the sine wave producing the capacity variation and that producing the sweep on the screen; this phase difference may' change as the reed moves toward the coil, or away from the coil. Such a change will cause the image on the screen to appear blurred or double.

In order to avoid this condition, this phase difference must either be cycle of the image must be blanked out, by apat the extreme ends Cmln and Cmax and it position correspondblanking potential during each half cycle of sweep. This will be shown in Fig. 9.

The advantage of the synchronous vibrating condenser is the great simplicity it ailords for making a panoramic receiver. ABy inserting a voltage controlling device in the exciting coil Il, the amplitude of the vibration can be so varied that it is possible to vcover wider or narrower visual bandwidths at will.

Due to the fact, however, that the instantaneous velocity of the reed varies, the resolution will be unequal, the maximum resolution being shown at the extremities of the screen and the lowest resolution in the center.

Such a vibrating condenser, with a. cathode ray oscillograph, can constitute a simple attachment to any ordinary type of receiver which will become a panoramic type receiver, or aural reception receiver, at will.

sine wave. '1"he velocity is I other is oil was pointed out above;

Fig. 9 shows the essential parts of such acomblnation. 15 represents a lconventional radio receiver having a manually tunable condenser 18. In parallel with this condenser is connected a vibrating condenser 82-63. The exciting coil voltage is derived from the secondary 11 of a power supply transformer through a switch 18 and a potentiometer 19. 'I'his controls the ainplitude swing of the vibrating reed 6l. The output of the receiver is connected to an aural device 88, and a switch 85 is provided for interrupting its operating when the vibro-condenser is in operation. Switches 18 and 85 can be operated simultaneously: when one is on the and vice-versa. The Vertical deflecting element 42 is also connected to the output of the receiver (detector or audio frequency amplifier). The horizontal element 43 is connected to the secondary 80 of the power supply transformer, through a phase shifting bridge 8|-8I, which shifts the phase by 90. This is necessary l"because the vibration of the condenser varies in phase with the current variation which is 90 out of phase with the voltage variation. From the same power supply voltage the blanking wave is supplied to the grid 88 of the cathode ray tube through condenser 89, as described above.

Ihe contro1s19 and 16 can be ganged together if desired, and the value of the potentiometer 19 can be made such as to maintain a substantially constant visual band width 'as the condenser 18 is rotated from minimum to maximum.

What has` been said about a vibrating condenser can be said about a vibrating inductance. Instead of moving the armature of a capacitor, the reed can move one or several iron cores in one or several coils. The combination of a variable capacitor 18 for manually tuning the receiver, with a periodically varying inductance has the advantage that the visual bandwidth W varies proportionally directly to the frequency rather than to the cube of the frequency as it this proves important for special applications.

As it has been pointed out, the combination between tunable channels, aural channels and a panoramic channel, can be extended further, to more complex combinations.

In the patent applications of Marcel Wallace Nos. 196,520 (Patent 2,219,151, supra) (Figs. 22, 23 and 37), 330,763 (Fig. 25) filed April 20, 1940, for Radio beacon altimeter and panoramic reception system, Patent 2,312,203, and 357,814, filed September 21, 1940, for Radio altimeter and panoramic reception system, it has been shown that due to visual retentivity, it is possible to use one panoramic visual receiving channel to simultaneously show different portions of the frequency spectrum on two different display surfaces.

Either mechanical or electronic switching methods have been shown in those applications to effect the synchronous operation of alternately selecting two different inputs (coils or antennas) and separate the outputs on two regions of the screen. l

The same methods can be used by substituting two different Tunable channels in the place of two different antennas or coils, and

either show them on two portions of acathode ray screen, or on two separate screens. An example of such a combination is shown in Fig. 10 in which two tunable channels are shown, operating to cover two bands of the spectrum: one for example from -130 mc., taking the airway beacons, which may be manually tuned; and another from 148-154 mc., covering vertical separation indicating beacons (such as described in application 357,814) and which may be tuned by an vaneroid cell. Each of the outputs of these two channels is passed through a coupling tube into a Panoramic channel. These coupling tubes are alterately blocked by means of a square wave voltage alternately applied to their grids, and act therefore as electronic switch No. 1 shown on Fig. l0. The square wave voltage generator, also shown, is synchronized with the sawtooth voltage'generated in the panoramic channel. The panoramic channel can be terminated either with two separate cathode ray tubes, or with one single cathode ray tube, as shown in the previous patent applications.

In the first case each tube is bianked out alternately by applying through an appropriate coupling device square wave voltage on their grids, in synchronism with the same square wave generators. This coupling device is shown on Fig. l0 as electronic switch No. 2; in the second l case,` the vertical deflection plates receive the square wave voltage so as to produce two parallel lines on the screen of the tube, corresponding to the two frequency sweep axes of the two channels.

As an addition to this combination, an Aural channel is shown, which can be connected by a switch, at willY to either of the two tunable channels, so that the operator can listen to the signals in the center of the screen on each channel.

While in this specification, and in some of the appended claims, we have referred to an aurally responsive means it is to be understood that such means may be any device, whether acoustic or electric, which may be made to respond or indicate the presence of an audio modulation, such as alternating current meters, rectifiers coupled to D. C. ammeters, vacuum tube voltmeters, etc. Such devices are sometimes also referred to, in the appended claims, as: audio responsive means." J

While we have described our invention in certain preferred embodiments we realize that modications may be made in the circuit arrangements and disposition of elements of apparatus and we vintend no limitations upon our invention other than may be imposed by the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A signal receiving system adaptable to be connected to a superheterodyne radio receiver having a signal selecting circuit and an intermediate frequency amplifier and an audio responsive device, a source of periodically varying voltage and electronic means controlled by the said varying voltage for periodically and automatically tuning the said signal receiving system over a wide frequency band extending equally above and below the frequency of the said amplifier, means for amplifying the ends more than the center of the said wide band so as to substantially compensate for the sharpness of the said s'gnal selecting circuit, and visual means operated in synchronism with the said periodically varying voltage for reproducing on a screen, in spaced relationship corresponding to their respective frequencies and amplitudes, the signals receiv- 'able over the said frequency band, said visual means operating simultaneously 'with and independently of the said audio responsive device.

2. A radio receiving system for simultaneously indicating the amplitude and frequency characteristics of all signals within a continuous but selectable band of the frequency spectrum, as well as the modulation of one of said signals, said system including an input channel, a manually tunable oscillator and a frequency converter, a signal-amplifying system tuned to a predetermined frequency and connected to the said converter followed by a detector and aurally responsive means connected to the said detector; a second signal amplifying system connected to the said frequency converter, means for periodically tuning the said second signal amplifying system over a wide band of frequencies extending equally above and below 'the said predetermined frequency, means for varying the width of the said wide band, and visual indicating means operating in synchronism with the said means 'for periodically tuning the second signal amplifying system, for indicating on a display surface in spaced relationship corresponding to frequency relationship, the signals present on the said wide band of frequencies, said aural responsive means and said visual means operating simultaneously and independently of each other.

3. Method of simultaneously observing the frequency and amplitude characteristics ofv all'signais present over a manually selectable band of the frequency spectrum, extending on each side of an vaurally received signal, with the aid of a tunable radio receiver provided with a signal conversion stage and terminated with aural reception means, including the following steps: deriving from a signal conversion stage of a manually tunable radio receiver all the signals present over a wide band of the frequency spectrum, periodically and successively selecting each elementary portion-of the said wide band including an aurally received signal at a predetermined sweep rate, amplifying each of the signals successively received at different degrees of amplification so as to compensate for the selectivity ofthe said receiver, detecting the said signals and visually indicating in spaced relationship according to their corresponding frequency relationship and at a rate equal to the said sweep rate, the amplitude of each Vof the detected signals.

4. A system for visually analyzing a continuous band of the radio frequency spectrum, of substantially constant and predetermined frequency bandwidth, said band being selectable over a wide range of the `spectrum, said system including an input channel followed by a first frequency conversion stage, a ilrst oscillator connected to the said first frequency conversion stage, means for tuning said oscillator, a second frequency conversion stage coupled to the rst, said second frequency conversion stage being tuned to accept a band pass equal to or greater than the bandwidth to be analyzed and coupled to the said first frequency conversion stage, a second oscillator connected to the said second frequency conversion stage, automatic means for periodically varying the frequency of the said second oscillator over a bandwidth equal to the bandwidth to be analyzed, an amplifier tuned over a narrow bandwidth representing only a fraction of the bandwidth to be analyzed and connected to the output of the said second conversion stage, a source of periodic sweep voltage operating in synchronism with the said automatic means and visual means operated in synchronism with the said sweep voltage for representing on a display surface in spaced relationship' according to their frequency difference the signals present over the band to be analyzed,

said band remaining of constant width independently of the frequency of the said first oscillator.

5. A system for visually anahfzing a continuous band of the radio frequency spectrum, as set forth in claim 4, wherein a ilxed frequency calibrated scale is mounted in ilxed relationship with the said display surface, for reading directly on the said scale the frequency relationship between the signals appearing on the said surface, independently of the position of the tuning means of the said receiving system.

6. A system for visually analyzing a continuous portion of the radio frequency spectrum, as set forth in claim 4, wherein means are provided for vadjusting at will the frequency bandwidth of the said periodically varying oscillator.

7. A system for visually analyzing a continuous band of the radio frequency spectrum, as set forth in claim 4, wherein an aural channel including a sharply tuned intermediate frequency amplifying stage is coupled to the output of said rst converter, said intermediate frequency stage being coupled to a detector, followed by an audio responsive device, whereby the said device operates simultaneously with. and independently of the said visual means.

8. Method of visually analyzing a band of the radio frequency spectrum having diiferent degrees of frequency resolution over its range, withl the aid of a tunable radio receiving system and a cathode ray tube having a cathode ray generator and a screen, including the'i'ollowing steps: proquency band in synchronism with the said periodically varying voltage, adjusting the rate of change of said varying voltage and of said tuning so that the regions of the band requiring the greatest resolution are tuned through at the slowmeans operating in synchronism with the said automatic means. j,

10. A radio receiving system as set forth in claim 9, wherein the said input channel has a wide bandpass characteristic and is" tunable within predetermined limits of the frequency spectrum. f l

11. A panoramic ing a signal input channel, a first oscillator, Vmanual means for tuning said oscillator over a predetermined range of the frequency spectrum, a first frequency converting stage coupled tosaid input stage and to the said first oscillator, a second oscillator, automatic means for periodically tuning said second oscillator within predetermined limits o f the frequency spectrum, adjustable means for varying the limits of the frequency spectrum between which the said second oscil lator is periodically tuned a source of periodically varying voltage operating in synchronism with the said last means, a second frequency converting stage coupled tothe said first converting stage and to the said second oscillator, a signal amplifier coupled to the said second converter and a visual output device coupled to the said amplifier and to the said source of periodically varying voltage. .l

12. Radio receiving system including va, signal receiving circuit, automatic means forA periodically tuning said signal receiving circuit over a predetermined frequency bandwidth, an amplifier coupled to the said signal receiving circuit, a detector coupled to the said amplifier and producing a series of electric pulses ofa duration equal to and of an amplitude proportional to the amplitude of the signalsl successively received, means for feeding back the said pulses into the said amplifier so as to reduce its amplifying char,- acteristics proportionally to the amplitudeof each said pulses and visual means operated inisynchronism with the said automatic means for'representlng on a display surface each ofthe said signals successively received, in the form ofvisual radio receiving system includchannel, adaptable to be operated in conjunction with a superheterodyne radio receiver, said ref ceiver having a signal selecting means, frequency conversion means, an intermediate frequency amplifier tuned to a frequency Fi, and audio responsive means, in the above order, and the said panoramic channel comprising: input means, including a bandpass filter for coupling the said panoramic channel tothe said frequency conversion means, said filter means being tuned to pass a band ,of frequencies centered at frequency Fl and exten ing over a width greater than w/2 cycles, on each side of frequency Fi, the passband characteristic of the said filter being non-linear and substantially compensating for the sharpness of response of the saidsignal selecting means, means for automatically and periodically tuning the said panoramic channel over a frequency band having a' constant width of w cycles and extending equally on each side of the said frequency, and visual means operating in synchronism with the said periodically tuning means, for indicating on a display surface, in spaced relationship corresponding to their frequency and amplitude relationship, the signal present over the said band of constant width, said visual means operating simultaneously with, and independently of, the said audio responsive means.

16. A panoramic receiver having a constant bandwidth, including a signal pre-selector circuit, means following the said circuit, including a local oscillator for converting the incoming signals into signals having an intermediate frequency, tuning means for the said oscillator, a bandpass filter having its center frequency tuned to the said intermediate frequency and having a non-linear amplitude characteristic to substantially compensate for the sharpness of the said signs separated by linear intervals proportional to the respective frequency intervals between the corresponding signals and at substantially logarithmic amplitude ratios. l

13. A panoramic radio receiving system whose center frequency is `tunable over wide, regions of the spectrum. and vwhich visually lindicates a band of constant width .of w cycles, independently of the region of the spectrum overv which it is tuned, said system including: a Atunable channel coupled to a panoramic channel, wherein the said tunable channel includes a signal selecting circuit and a frequency converting circuit in the order named, tuningv means for the said circuits.

a bandpass filter means following the said converting circuit, said filter means being tuned to pass a iixed and predetermined band of the spectrum of a width greater than w cycles, said panoramic channel including automatic frequency scanning means covering a band of w cycles and whose center frequency corresponds substantially to the center of the said predetermined band.

14. A panoramic radio receiving system, as set forth in claim 13, wherein the said bandpass filter means is coupled to an independent aural channel. including a signal amplifying circuit tuned to a frequency within the passband of the said filter, followed by a detector and an audiovresponsive device, so that a signal shown on the panoramic channel is simultaneously audible in the said audio responsive device.

15. A receiving system including a panoramic pre-selector circuit, said filter circuit being connected to supply said intermediate frequency signals to a plurality of signal channels, one of said channels being periodically tunable over a band of constant width and situated within the pass band of the said filter, and meansfor visually indicating on a display surface all signals receivable within the said band of constant width, at intervals corresponding to their respective frequency separation, and another of the said signals channels including a filter means and a detector, in the order named, said filter means having a pass range which is narrower than, butk situated within, that of the first ffllten said detctor being followed by an aural responsive dev ce.

17. A panoramic receiver having a constant bandwidth as set forth in claim 16, wherein the pass range of the said filter means is situated in the center of that of the first filter.

18. A panoramic receiver having a constant bandwidth as set forth in claim 16, wherein the said filter means includes tuning means for situating its pass range over` any portion of the pass range of the first filter.

19. The method of panoramic reception for securing an optimum degree of resolution which includes: receiving a band of the spectrum of a width of p cycles and periodically displacing this band, at a rate of f cycles per second over a wider band having a width of w cycles wherein the value of p is made greater than V0.2 wf, converting all signals received over the said band of w cycles into visual signs and spacing the said signs lproportionally to theA difference of frequency between corresponding signals, the resolution between the said visual signs being of the order of VPH-2 wf.

20. A panoramic radio receiving system having an optimum degree of resolution, including automatic frequency scanning means, said means pei riodically covering a band of the spectrum of a Width oi' w cycles and at a rate of f cycles per second, lter means following the said scanning rPatent N o. 2,381,940.

Certiicate of Correction August 14, 1945.

MARCEL WALLACE, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, second column, line 18,

for the word unit read um'ty: page 4, first column, line 35, for the equation page 9, second column, line 48-49, claim 16, for signals read. szgnal: and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 1st day of January, A. D. 1946.

[sEALl LESLIE FRAZER,

First Assistant Commissioner of Patents.v

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