US2245731A - Automatic band-width regulation means - Google Patents

Description

June 17, 1941. H. SPREINE AUTOMATIC BAND-WIDTH REGULATION MEANS Filed June 13, 1939 A vc Jam/ML INVENTOR HEINRICH SPR E/NE BY #5! I ATTORNEY Patented June 17, 1941 FFICE AUTOMATIC BAND-WIDTH REGEEATION MEANS Heinrich Spreine, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. 11., Berlin, Germany, a corporation of Germany Application June 13, 1939, Serial No. 278,838 In Germany June 16, 1938 Claims. ((31. 250-) Arrangements are known in the earlier art for providing an automatic band-Width variation in receiving apparatus in which the band-width is automatically varied as a function of the signal strength in such a way that the band-width is made small when the incoming or signal intensity is reduced, while it is made large when the signal strength is large.-

Arrangements of this kind are rather complicated and expensive when the band-width is varied not merely in a single circuit, but in several circuits simultaneously, and also if this variation is accomplished not by a variation of the damping, but change in coupling. According to prior practice, variation in the coupling has been efiected mostly by a mechanical adjustment of coupler coils. However, such ire-adjustment of the coupling requires considerable mechanical power; indeed, this power where automatic regulation is to be effected by tube circuits would be obtainable only by the use of tubes of large power.

According to the present invention, the means designed to produce band-width variation, which a mechanical restoring or retractile force tends to force constantly in the direction of minimum band-width, is coupled by mechanical means with the tuning shaft of the receiving apparatus in such a way that when the tuning shaft is turned the band-width is enlarged. But the said coupler or loclnng means is operative only above a certain threshold value of the signal strength.

The advantage underlying the invention is that the power required for a mechanical adjustment of the band-width is furnished by the user of the set. In fact, the signal oscillation is merely called upon to render the coupling means operative, and this requires a substantially lesser expenditure of power. The band-width variation means, therefore, may be built the same way as has heretofore been customary, that is, for instance, with mechanically adjustable coupler coils. If the amplitude of the signal oscillation is equal to zero or very small, then the bandwidth varying device by action of the retractile force is so adjusted that the band-width assumes a minimum value. However, as soon as in the course of the tuning of the set the latter is roughly tuned to a certain station, then the coupling device becomes operative, and the bandwidth regulator is driven by the tuning means which must be turned another distance for exact and sharp tuning, with the result that the bandwidth is enlarged. The band-width which will be finally adjusted in the receiver will be so much larger, the stronger the signal of the incoming transmitter station since in the case of a powerful transmitter a certain threshold value will be attained by the signal intensity even when the set is still a greater distance away from sharp tuning than in the case of a station whose signal comes in feeble. This situation will apply to all receivers with a normal selectivity curve in which the automatic volume control does not equalize completely.

An exemplified embodiment of the invention is illustrated in the appended drawing in which the single figure discloses so much of a radio receiver as is necessary for a proper understanding of the invention. The coils L1 and L1' wrapped on a form or support shall be assumed to form the two coils of a tuned I. F. band-pass filter of the receiving apparatus. Coil L1 is in coupling. relation with the coil L1 by means of the coupling coil K1 comprising only a few turns and being connected in series with it. In the position shown in the figure, the coupling is very weak since the axes of the coils L1 and K1 are at right angles to each other. If, then, coil K1 which is revoluble about the shaft M1 is moved out of its normal position towards any side at all, the coupling at all events becomes stronger and the band-width is thus enlarged.

The coils L2, L2 shall be assumed to constitute, in a similar way, a second I. F. band-pass filter; they shall be coupled with each other by the coupler coil K2 which is turna-ble about the axis M2.

The turning of the coupling coils is effected by the lever arms A1 and As the lower ends of which are secured to a metal band B. The latter at both ends is connected by way of tractile springs F1 and F2 with the stationary casing of the receiver and it is passed over rollers R1 and R2 and a drum T. The latter consists of a semiconductive material such as agate or marble, for instance. The shaft W thereof is in mechanically coupled relation, on the one hand, with the shaft of the tuning condenser C, and, on the other hand, with the tuning knob K. The drum, for instance may be secured directly on the shaft of the tuning knob K which is coupled with the rotary condensers by a chord or cable.

The springs F1 and F2 are of such dimensions that normally the coupler coils K1 and K2 will occupy the position as shown. The ribbon or band B is placed on the smooth drum T so loosely that even when the tuning knob K is rotated rather rapidly the normal position (or rest) is practically unchanged.

In sliding contact with the drum is a metallic brush S by way of which the drum is fed with the D. C. voltage obtained by rectification of the I. F. oscillation and which serves at the same time for automatic volume control. As soon as the drum in reference to the grounded band B has a potential which surpasses a certain minimum level, strong forces of attraction will be set up between the band and the surface of the drum by virtue of the well-known Johnson- Rahbek effect as a result of the increased adhesion between the two boundary layers, and this sets up appreciable friction. The result is that the band is driven by the drum and thus by the tuning knob, and the coupling coils K1 and K2 are turned with the consequence that the coupling and the band-width of the receiving apparatus are increased.

The amount of increase of the band-width when tuning to a station is a function of the angular range covered by the tuning shaft figured from the position in which the abovethe drive.

The control potential may be amplified by a D. C. amplifier. t is alsopossible to cause the rectified signal oscillation to actuate a relay above the threshold value, the relay causing a potential which is high with respect to ground to be impressed upon the drum.

Under certain circumstances also the I. F. potential itself may be applied to the drum or the band.

where the tuning is eifected not manually, but by motor drive, and where the adjustment to a definite station is caused by the actuation of a coordinated press button. If for this purpose the tuning means are so designed that the adjustment occurs only in one direction, then the bandwidth variator as usual may be so designed that from the position of minimum band-width it can be changed in only one direction.

What I claim is:

1. In a receiving system, a band-pass network provided with means for varying its signal response characteristic, means for tuning the receiver to a selected station, and means under the direct control of the tuning means and movable in response to the strength of the received signal for automatically adjusting the signal response varying means.

2. In a receiving system, a band-pass network,

means for varying the signal response charac-' teristic of said network from a condition of sharp selectivity to one of high fidelity, means for tuning the receiver to a selected station, and means under the direct control of the tuning means and movable in response to the strength of the received signal for automatically adjusting the signal response varying means, said response varying means normally providing a sharp selectivity adjustment up to a predetermined value of signal strength, and for increased signal strength be- The invention will be found useful also in cases yond said value providing varying degrees of high fidelity adjustments. I

3. In a receiving system, a band-pass network provided with means for varying the width of the band transmitted thereby, means including a control shaft for tuning the receiver to a selected station, and means under the control of the tuning means and responsive to the strength of the received signal for automatically adjusting the band width varying means, said adjusting means comprising a member connected to the band width varying means and adapted to be selectively operable by the tuning control shaft, said member normally maintaining said varying means innarrow width adjustment, and means for establishing between said member and the control shaft a potential difference proportional to the signal strength, a minimum potential difierence being required to cause the control shaft to operate the member, the arrangement being such that during the process of tuning, for received signals, below the minimum value the member is inoperative and the adjustment of the network is such as to pass a narrow band, whereas for received signals above said value the control shaft operates to move said member and consequently the band width varying means for adjusting the network to pass a wide band.

4. In a receiving system, a band-pass network provided with means for varying the width of the band transmitted thereby, means including a control shaft for tuning the receiver to a selected station, and means under the control of the tuning means and responsive to the strength of the received signal for automatically adjust ing the band width varying means, said adjusting means comprising a member contacting with the tuning control shaft and connected to the band width varying means, said member nor mally maintaining said varying means in narrow width adjustment, and means for establishing between said member and the control shaft a potential difference proportional to the signal strength, a minimum potential difference being required to cause the control shaft to frictionally engage and drive the member, the arrangement being such that during the process of tuning, for received signals below the minimum Value the frictional coupling between shaft and member is insufficient to move the latter and the adjustment of the network is such as to pass a narrow band, whereas for received signals above said value the frictional coupling is sufficient to move said member and consequently the band width varying means for adjusting the network to pass a wide band.

5. In a receiving system, a band-pass network provided with means for varying the width of the band transmitted thereby, means including a control shaft for tuning the receiver to a selecte station, and means under the control of the tuning means and responsive to the strength of the received signal for automatically adjusting the band width varying means, said adjusting means comprising a semi-conductive sleeve mounted on the control shaft, a metal strip adapted to rest on said sleeve and having a connection to the band width varying means, spring means for normally urging said varying means to the narrow width adjustment, anda brush contact rid ing on the semi-conductive sleeve and having a potential proportional to the signal strength impressed thereon whereby there is established between said band and sleeve a potential difference proportional to the signal strength, a minimum such as to pass a narrow band, Whereas for received signals above said value the frictional coupling is sufficient to move said band and. consequently the band width varying means for adjusting the network to pass a wide band.

HEINRICH SPREINE.

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