US2044229A - Ultra-short wave auxiliary apparatus for radio receivers - Google Patents

Description

June 1936- K. SCHLESINGER 9 ULTRA-SHORT WAVE AUXILIARY APPARATUS FOR RADIO RECEIVERS Filed Nov. 29, 1953 Jn yen/0r:

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Patented June 16, 1936 PATENT @FFEQE ULTRA-SHORT WAVE AUXILIARY APPA- BATUS FOR RADIO BEGEIVERS Kurt Schlesinger, Berlin, Germany 4 Claims.

The subject matter of the invention is an ultrashort wave circuit for radio receivers.

The apparatus according to the invention consists of an oscillatory circuit and a tube, which at the same time serves for generating the heterodyne frequency, rectifying the short-wave frequency received, and for mixing these frequencies, and which conveniently may be connected to an intermediate frequency amplifying stage. It is desirable according to the invention to unite both stages to form a multi-stage tube.

The circuit arrangement enables a large wave range, for example of 4-200 meters, to be covered without difiiculty, which in accordance with the invention is accomplished by the fact that all necessary impedances in connection with the leads for the grid and the anode are produced by highly ohmic resistances as poor as possible in capacity, but not by chokes. As feed-back connection there is provided fundamentally a capacitative threepoint connection. According to the invention there are employed for the capacitative distribution of the potential, not special condensers, but the capacities Cak and Cgk existing in the tube upon the assembly.

The invention may be more fully understood with reference to the accompanying drawing, which shows by way of example several connection systems.

Herein Fig. 1 illustrates diagrammatically an ultra-short wave circuit for radio receivers,

Fig. 2 illustrates a modification of the aerial coupling circuit device,

Fig. 3 illustrates a modification of the coupling of the auxiliary apparatus to a radio receiver.

Referring tothe circuit shown in Fig. 1, l is the oscillator tube, and 2 the oscillatory circuit, which is disposed in direct fashion between the anode 3 and the grid 4 of the oscillator tube. The cathode 5 of the tube is linked up with a medium oscillation potential which, as already stated, is correctly adjusted automatically by the tube and assembly capacities. The feed of the direct potential to the anode and the grid takes place, according to the invention, through the medium of two highly ohmic resistances, which are as poor in capacity as possible. It has been found in practice that the reception of ultra-short waves (digit waves) is only possible over a very large range of the rotating plate condenser, for example 1:3 and more, if the capacity parallel to this anode resistance is in the first place as small as possible, and secondly, is in correct ratio to the capacity between grid and earth. This capacity ratio must be selected so as to be approximately equal to the reciprocal of the tube employed.

In the case of assembly poor in capacity and small dimensions of the oscillatory circuit, it has been found that even capacities parallel to the anode resistance R of approximately -20 cm.,

such as result, for example, in the case of wire wound potentiometers, render the generation of oscillations impossible. The anode resistance must accordingly be made as poor in capacity as possible. For this reason the location of the resistance in the oscillator tube itself is of great advantage.

The oscillations produced with this circuit arrangement are very stable, and possess a large amplitude, particularly when employing modern tubes having a steepness amounting to 2-3 m. a./bolts and reciprocals of approximately 4%. According to the invention, tubes should be employed having the largest possible reciprocal (approximately 10%), as otherwise the appertaining capacitative distribution of the potential requires to be particularly formed, for example in the case of screening grid tubes the capacity Cak, with otherwise exactly similar conditions, would require to be formed in special manner.

It is possible in the case of this connection system in the first place to keep the losses in the oscillatory circuit within relatively narrow limits, and secondly, to perform a switching over of the wave range of 1:50, which under certain circumstances would not be capable of being employed in connection with other connection systems on account of the additional losses. For the arrangement according to the invention there may be employed a condenser with fixed dielectric in conjunction with a coil, which is tapped for example at four points after 2, 4, 12, and 28 turns. In this connection there may be covered with every adjustment of the coil a continuous wave range of 1:3, and at the same time the wave ranges 5-14 meters, 8-23 meters, 15-44 meters and 40-120 meters may be included. This changeover in the wave length takes place according to the invention by short-circuiting the parts of the coil 9, which are not used, with the assistance of a single-pole reversing switch. A single-pole reversal of this kind is an essential advantage of the oscillator connection system according to the invention, and fundamentally cannot be accomplished with other circuit arrangements, for example with the inductive three-point connection system or with the transformer-coupled connection. In this connection all rotary grips, for example for the rotating plate condenser 8 and for the change-over switch 55, require to be separated from the poles, for example by means of insulating sleeves, and passed in earthed fashion towards the outside. Upon operation of the connection system it will be found that upon reversing the polarity of the connections between tube and oscillatory circuit one connection system is superior to the other, which is explained by more favourable value of the capacitative distribution of the potential in relation to the reciprocal of the tube. That particular polarityshould be selected in which the amplitude produced is the greatest.

The oncoming aerial oscillation is conducted to the heterodyne for the purpose of producing the intermediate wave. It has been found in practice that the strength of the intermediate wave continuously increases if the aerial is not coupled in the usual manner with an input circuit connected with cathode and grid but is coupled with the anode. According to the invention, therefore, the aerial is coupled firmly with the anode of the oscillator tube. The efficiency of the arrangement is very good for the reason that the oscillation amplitude of the local oscillation is very considerable, and this enters in product together with the rectifier effect into the total eificiency. The operation of the arrangement may be further improved if the tube is working with grid-current rectification. For this purpose there is introduced between resistance 1 and earth ID a positive bias, whereby the anode by-pass condenser ll acts as audion condenser.

The switching elements may conveniently be selected as follows:

R (7) :10 ohms; Ra(6) =3'10 0(8) :300 cm.,

diameter of oscillatory coil 20 mm., winding-copper wire of small cross-section (.l-.2 mm.), silk, single layer closely Wound, coil holder Pertinax. The fitting of the coil takes place in such fashion in accordance with the invention that the wire is spaced at least to the extent of 5 mm. on all sides from insulating materials. Metal has been found to have no detrimental effect either inside or outside the winding, and causes merely detuning, while insulating materials, for example Pertinax, may produce damping effects of such nature in the vicinity of the coil that the oscillations disappear. Thus, for example, it is possible to place closed metal cylinders for screening purposes about or against the coil, without providing in these cylinders longitudinal slots. It is advisable, therefore, to employ only good conductive materials.

Considerable difficulties exist when connecting an auxiliary apparatus of the present kind, more particularly for ultra-short waves, with a highly selective radio receiver. In the case of sound telegraphy the frequency band amounts to approximately 100, in the case of highly selective telephony to 10,000 and in the case of television transmissions to 100,000 periods. The 10- cal oscillation frequency must be constant to within 10% of the frequency band. Accordingly the constancy of the local heterodyne with 7 meters wave length must amount in the first case to approximately 10, in the second case to approximately 10 and in the third case to approximately 10- It has been found that it is extremely difficult to attain such a high constancy of the oscillator. It has been ascertained that in the case of the usual arrangements a variation in capacity of approximately 10- cm. Cak, i. e., a variation which is caused alone by movement of the human body in the vicinity of the aerial (even at a few meters away from the aerial) produces inadmissible detuning.

It is known that this influence may be diminished by placing a very small condenser l2 of approximately .1-1 cm. between the aerial and the oscillatory circuit. At the same time both the oscillatory circuit as well as its leads require to be screened off, for example, arranged in an armoured box l3. The aerial coupling is so constructed that the desired ultra-short reception wave is transmitted practically entirely to the receiver, whilst the long waves, and more particularly waves of the length of the intermediate wave to be adjusted, are completely withheld from the receiver. This is accomplished by CR or CL couplings, for example the aerial may lead in through the medium of a condenser M, the resistance of which merely requires to be small in respect of short waves, but the resistance of which in respect of long waves should exceed that of the resistance l5 by between ten and one hundred times the amount, for example C14=25 cm., R15=200 ohms. The resistance I5 is preferably made so small that it just fails to constitute an inadmissible damping in respectoi the oscillatory circuit 2, with which the same is situated in parallel in series with the coupling condenser l2.

In place of the described combination with a odic, but on the other hand for television pur poses fully aperiodic systems, which safely with-- hold aperiodically from the receiver the waves of more than 200 meters in length.

The aerial coupling as set forth has the advantage of particular sensitiveness, and from a practical point of View may be regarded as adequate for the majority of purposes. It possesses, how-- ever, the disadvantage that the aerial radiates and also reveals a slight detuning effect. The connection system illustrated in Fig. 2 enables the stated disadvantages to be wholly avoided.

In Fig. 2, 4! is the oscillator tube with grid 12 and anode 43, and 44 the oscillatory circuit. The cathode 45 is disposed at the casing 46, which must be regarded as capacitatively earthed. The earth capacity is represented by the condenser 41, and earth by the reference numeral 48. According to the invention, the aerial 39 is linked up with the middle armatures 50 of a differential condenser, which has the outer armatures 55 52. The latter are connected with the oscillatory circuit. The armature 50 is adjusted until the coupling potential is equal to the earth potential, which in accordance with the connection system will require to be the case in respect of a certain middle position between the terminals of the oscillatory circuit. By the use of a metallic box including the oscillatory circuit all the capacities are defined at any time. The poles of the oscillatory circuit have capacities 53, 55 in relation to the box amounting perhaps to several 10 cm. The differential condenser 58, 5|, 52 must be smaller to the extent of at least one order of magnitude i. e. ca. 1 cm. In this manner it is accomplished that by adjustment of the differential condenser the potential ratio between circuit poles and box is not changed. There is accordingly found at 50 the desired zero position of the oscillator point as against the anode, so that no heterodyne oscillations can be transmitted by the aerial. The circuit, therefore, also cannot be detuned. The oncoming wave meets against grid and anode of the oscillator tube with the same phase (but with unequal amplitude), and is completely decoupled against the heterodyne cirand 'cuit 44. Rectification,therefore'takes place in the tube 4!, in the same fashion as if this tube were a diode with certain equivalent dimensions. In consequence a good efficiency in the transmission of the received energy to the tube is only eatpable of being obtained if the aerial impedance is small as compared with theresistances of the capacitative by-passes- 53 and :54. According to the invention, the box, therefore, is made as large as possible, in order to diminish these capacities to every possible extent. Even when employing the aerial coupling according to the invention detunim is still possible, and this may be caused by hand capacity at the receiver output, at the mains portion, or even in the leads from the mains to-the receiver and at the rotary grips of the afterconnected radio apparatus.- This detuning takes place by reason of the fact that residual traces of the ultra high-frequency oscillations are present at these points. To avoid these disturbances the after-connected intermediate frequency amplifier I8 is, in accordance with the invention,so 'coupled at the oscillator I that the ultra highfrequency is transmitted to its grid only with difficulty. For this purpose there may be employed, for example, a metallic screening means l9 within the two-stage tube, or a resistance 25, assuming that the capacity parallel thereto possesses practically no conductivity as compared with its low value of approximately 500 ohms.

The amplifying stage It is connected with the output by means of a choke or a resistance and a condenser 2 1, whereby the dimensioning (201500 ohms or windings, 21:10 cm.) is so chosen that the intermediate wave is allowed to pass as completely as possible, and the ultra-high frequency currents by-passed to ground. The anode choke must be small in dimensions as compared with the anode resistance 20, and poor in capacity. The self-capacity should preferably amount to less than one-tenth of 2i.

The heating leads are throttled by low-frequency chokes 22, 23, which preferably do not affect each other, or only in co-phasal fashion. The frequently very powerful residual traces of oscillation penetrating into the mainsencounter resistance in the chokes 2 3 or 25. The latter may be dispensed with if the capacity of the rectifier tube 26 is suinciently small. Disturbing oscillations proceeding in capacitative fashion over the transformer are withheld from the mains lead by the chokes 27. The throttling effect may be improved and made aperiodic by means of a condenser 28 of approximately 200 cm.

The coupling of the auxiliary apparatus may be performed particularly conveniently in accordance with Fig. 3 also in such fashion'that in place of a choke or resistance coupling an inductive coupling takes place by means of a transformer 3 35. According to the invention, there is performed in this connection a reducing transformation preferably of approximately 4:1, in order in this fashion to obtain favourable adaptation to the after-connected radio receiver. In addition, the secondary coilis preferably furnished with a plurality of tappings.

In order to reduce dispersion as far as possible down to a minimum, the secondary coil (approximately 100 windings) is preferably encompassed by the primary coil (approximately 400 windings), and a tight coupling is thus obtained. It has been found convenient to select the average coil diameter at approximately mm. The diameter of the wire amounts in the case of the primary coil to .1 'mm.', whilst in the case of 'thesecondary coil it is .3 mm.

The primary coil 34 represents practically a complete short-circuit in respect of ultra-short waves, so that the latter are withheld from the after-connected radio receiver. For final preclusion of the ultra-high frequencies the secondary coil 35, in accordance with the invention, is surrounded by an armouring in the form of an earthed network 40. For the purpose of best possible transmission of the intermediate wave" a damped choke 38 raised to resonance may, in accordance with the invention, be conne'cted'between the grid of the stage l8 and earth. "The choke 38 may also be tuned to the adjusted intermediate wave by means of a special parallel block, and preferably damped by a parallel resistance. The mains anode must be Well steadied, as the smallest oscillations on the part of the anode potential result in inadmissibly large fluctuations of the superposed frequency. Steadying may be performed with the assistance of two large condensers, preferably electrolyte condensers'29, in conjunction with 'a highly ohmic resistance 3|. Steadying in respect of the first stage (the oscillator stage) is, in accordance with the invention, efiected separately. Even in the caseof extremely well steadied anode potential an appreciable fluctuation of the frequency remains, which is due to the A. C. heating. The applicant has found that in the case of technical cathodes of the indirect type the grid effect of the ends of the filament, which eifect is very small in itself and otherwise i is hardly taken into consideration, is sufficient in the present case to disturb the reception. To

preclude these disturbances there is provided either according to the connection system a potentiometer 30 parallel to the heating line but behind the protective chokes 22, 23. By passing a suitable point (zero point) of this potentiometer to earth, it is possible to overcome this fluctuation to an extent sufficient from a practical point of view. It is particularly convenient to unite the important potentiometer 30 structurally with the tube, for example by fitting the same into the base of the tube, in order in this manner to be able to supply tubes completely free of humming effect and capable of being exchanged. It is, however, also possible in accordance with the invention to avoid structurally the grid effect of the ends of the filament by screening off the ends of the filament against the cathode Within the tube.

The after-connected radio apparatus is assumed to be a recceiver with ordinary transformer coupling of the aerial, in the input circuit of which there is then connected in constant fashion the transformed resonance resistance of the receiver primary circuit in an order of magnitude of several 10,000 ohms. .Itis possible, thereerably the capacity of the condenser l6 amounts for example to 25 cm., and the resistance l'l'to .1 megohms, whereby humming is overcome. Direct connection of the grid of l8 with the anode point 33 is also conceivable in itself. By reason of the bridge connection 30 according to the invention a point entirely free of humming sound may also be adjusted if in addition to the heat ripple anode ripple is also present, as all phasic conditions occurring are governed at the potentiometer 30.

It is specifically pointed out that the ultrashort wave auxiliary apparatus according to the invention requires to possess the following features in combination for attaining reception wholly free of disturbance over a range of approximately 4-200 metres and with a continuous range of for example 1:3 on each occasion in every position of the wavelength changing switch:

1. Production of all necessary impedances at the leads to the grid and the anode of the oscillator tube by highly ohmic resistances poor in capacity, whereby the ratio between the capacity of the anode resistance and the grid-earth capacity should be approximately equal tothe reciprocal of the tube employed.

2. Embodiment of the aerial in such fashion that waves of the order of the intermediate frequency wave are withheld from the auxiliary apparatus.

3. Aerial coupling over a very small condenser or over a differential condenser, which requires to be adjusted in such fashion that the aerial point for the oscillatory circuit is linked up with earth potential, in such fashion that the aerial does not radiate the oscillator vibrations.

4. Means for withholding the ultra-frequency from the output of the auxiliary apparatus, the mains and also the operating grips.

5. Means for precluding the disturbing control effect of the ends of the filament occurring upon the use of cathodes indirectly heated by alternating current, and if necessary also the auxiliary emission of the ends of the filament.

A considerable improvement in the efliciency may be obtained 1. by the use of screening grid tubes in the after-connected intermediate frequency amplifier stage (whereby it is desirable to assemble the oscillator and intermediate frequency amplifier stages, if necessary separated from each other by suitable screening means, in one single tube), and

2. by the use of a reducing transformer at the output of the apparatus, which may conveniently be furnished with a plurality of tappings in order to permit of adaptation to the radio receiver connected in different ways.

It is particularly convenient in accordance with the invention to furnish the tubes or the tube with suitable means which enable the microphone effects to be avoided. Further, it is desirable to mount the total auxiliary apparatus as far as possible to be free of shock, for example on rubher.

I claim:

1. In an ultra-short wave receiving system an aerial and a frequency changer consisting of an intermediate frequency amplifier and an electronic tube serving at the same time for generating an ultra-high heterodyne frequency, for amplifying the ultra-high frequency to be received and for producing the intermediate frequency by mixing and rectifying both ultra-high frequencies, an oscillating circuit tuned to the heterodyne frequency being connected to the grid and via a condenser to the plate of said tube. automatically back-coup1ed by the inner capacities of said tube, the plate of said tube being connected via a condenser to said aerial, and a high ohmic resistance as poor in capacity as possible, inserted in the plate circuit of said tube for coupling said tube with the intermediate frequency amplifier.

2. In an ultra-short wave receiving system an aerial and a frequency changer consisting of an intermediate frequency amplifier and an electronic tube serving at the same time for generating an ultra-high heterodyne frequency, for amplifying the ultra-high frequency to be received and for producing the intermediate frequency by mixing and rectifying both ultra-high frequencies, an oscillating circuit tuned toihe heterodyne frequency being connected to the grid and via a condenser to the plate of said tube, automatically back-coupled by the inner capacities of said tube, the plate of said tube being con nected via a condenser to said aerial, and a high ohmic resistance as poor in capacity as possible, inserted in the plate circuit of said tube for coupling said tube with the intermediate frequency amplifier, said high ohmic resistance placed in the tube itself.

3. In an ultra-short wave receiving system an aerial and a frequency changer consisting of an intermediate frequency amplifier and an electronic tube serving at the same time for generating an ultra-high heterodyne frequency, for amplifying the ultra-high frequency to be received and for producing the intermediate frequency by mixing and rectifying both ultra-high frequencies, an oscillating circuit tuned to the heterodyne frequency being connected to the grid via a condenser to the plate of said tube, automatically back-coupled by the inner capacities of said tube, the plate of said tube being connected via a condenser to said aerial, and a high ohmic resistance as poor in capacity as possible, inserted in the plate circuit of said tube for coupling said tube with the intermediate frequency amplifier, a differential condenser the moving plate of which is connected to the aerial and the fixed plates of which are connected to said oscillating circuit for adjusting said condenser in such a manner that aerial and oscillating circuit are decoupled for the heterodyne frequency.

4. In an ultra-short wave receiving system an aerial and a frequency changer consisting of an intermediate frequency amplifier and an electronic tube serving at the same time for generating an ultra-high heterodyne frequency, for amplifying the ultra-high frequency to be received and for producing the intermediate frequency by mixing and rectifying both ultra-high frequencies, an oscillating circuit tuned to the heterodyne frequency being connected to the grid and via a condenser to the plate of said tube, automatically back-coupled by the inner capacities of said tube, the plate of said tube being connected via a condenser to said aerial, and a high ohmic resistance as poor in capacity as possible, inserted in the plate circuit of said tube for coupling said tube with the intermediate frequency amplifier, said oscillatory tube, the tubes of said intermediate frequency amplifier and the coupling elements between both tubes being arranged in a common vessel.

KURT SCI-ILESINGER.

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