US2125723A - Interference elimination - Google Patents

Description

Auggz, 193s.

' FIL 75 F02 v c. HENRIQUEZ ET Al.

INTERFEHENCE ELIMINATION Filed April 15, 1936 40X/L Mfr esci/nie.

7" 0567A LA 0B INVE OR WWA/V CUHATHE//R/OUEZ BERN/117005 DJI. ELLEGE/V ATTORNEY Patented Aug. 2, 1938 PATE Application April 15, 1936,` Serial N o. '14,428

In Germany May 14, `1935 `V i 3 claims. (ci. 25o-2mV I'his invention relates to an improved method of eliminating interference in the wireless transmission o-f intelligence.

For the suppressionr of atmospheric disturbi ances and the like in the reception of intelligence transmitted by wireless it has previously been proposed to .render the high or intermediate frequency amplifier of the receiving apparatus inoperative when such disturbances arise, either by automatically increasing, when interference occurs, the damping of thetuned high or intermediate frequency circuits or by reducing the amplification of the high or intermediate frequency amplifying tubes by means of a variation of the grid bias.

However, these, known methods do not lead to the purpose in view as when the high or intermediate frequency portion of the receiver is `rendered inoperative theinterference proper is suppressed, it is true, but at theY same time the carrier wave of the signal received is also suppressed with the result that necessarily at the demodulation rectifier of the receiver a new disturbance is set up which becomes perceptible in the reproducing apparatus.

This adverse conditionrenders the effect of the above described method of eliminating interference illusive. It is, therefore, an object of our invention to provide means for avoiding the aforementioned difficulties. The transmission of the communications to be transmitted is effected, in accordance with the invention, in such manner that in the transmitter or in the receiver the carrier wave is suppressed when interference occurs, and then the high or intermediate frequency portion of the receiver is made inoperative.

Circuit arrangements for the suppression of the carrier wave and, if desired, of a side band on the side of the transmitter are known. In one of these known circuit arrangements the modulation stage of the transmitter consists for example, of two tubes in push-pull connection to the control grids of which the high frequency is supplied cophasally whereas the low frequency to be modulated on the high frequency is supplied counterphasally.` In this case one obtains in the output circuit of the modulation stage a modulated high frequency in which the carrier wave is suppressed.

Circuit arrangements for the suppression of the carrier wave in the receiver are also known. In these arrangements use is frequently made of lters composed of piezo-electric crystals.

Whether the carrier wave is suppressed on. the

sideY of the transmitter or on the svidgejof the ceiver, in either caseit has to be` added again"` in the demodulation stage `by generating.T tliis'. carrier wave anew in the receiver by` mean'sof,v aj suitablegeneratonm: l 31,411 i The accompanying drawing" shows,` by AWayiof example, two preferred' embodiments of the invention. Fig. 1 is a circuit diagram illustrating one mode o-f execution, while Fig. 2 shows an alternative circuit arrangement, both embodiments, however, being for the elimination of interference in which the carrier Wave is suppressed on the side of the receiver.

Into the input circuit of a high frequency amplifier H. F. is: connected a filter F which suppresses the carrier wave of the signal received and passes the modulation side bands. The latter are amplified in the high frequency amplifier H. F. and supplied, together with the oscillations generated by a local oscillator O, to a demodulation rectifier G1, the frequency of said Ilocal oscillation being equal to that of the suppressed carrier wave. The rectifier G1 is followed by a low frequency amplifier N. F. and by a reproducing apparatus, for example, a loudspeaker L. A connection is tapped from the output circuit of the high frequency amplifier to an auxiliary rectifier H which has a threshold value such that in the absence of interference no current flows in the rectifier. When a disturbance of suitable value arises the threshold value is surpassed and a current flows in the rectifier. This current controls the amplification of the high frequency amplifier by a grid bias variation of the amplifying tubes in such manner that the amplification is reduced and that the interference has no effect in the next portion of the receiver. In order to ensure that the circumstance that the high frequency amplifier is suddenly rendered inoperative does not give rise to new interference due to the fact that the tuned oscillatory circuits of the amplifier are excited in their natural frequency, it is advantageous to connect a filter F1, into the lead going from the auxiliary rectifier to the high frequency amplifier. 'Ihe task of said filter is to suppress that frequency component comprised in the voltage impulse supplied by the auxiliary rectier to the grids of the arnplifying tubes, whose frequency corresponds to the natural frequency of the tuned oscillatory crcuits of the amplifier. 'Ihe filter F1 may consist, for example, of a tuned oscillatory circuit which is tuned to the same frequency as is the high frequency amplifier. Better results than those afforded by the circuit arrangement shown may sired, an electric time lag or delay circuit DC may be connected between the filter l5' and the high frequency amplifier H. F.

We claim:

1. A radio receiver having a AfilterrforV damping f the carrier component of an incoming modulated wave, a high frequency amplifier fed with energy' from said filter, a local oscillatorand defmodulator for deriving a low frequency Wave from the output of said amplifier, a utilization device fed L with said low frequency wave, an auxiliary rectifler connected to the output circuit of said high frequency amplifier, and means including a resonant circuit tuned to the frequency of said high frequency amplier and connecting between the input side thereof and the output side of said auxiliary rectierfor blocking said amplifier in response to interfering and static energy.

2. A radio receiver having a lter for damping the carrier component of an incoming modulated l wave, a main high frequency amplifier fed with l' energy from said lter, a local oscillator and dex modulator for deriving a low frequency wave from-the output of said-amplifier, a utilization device fedA with said low 'frequency Wave, means including an auxiliary rectifier having an output circuit connected to a resonant circuit and thence tothe input side of said high frequency amplifier for blocking said amplifier in response to interfering and static energy, said resonant circuit being tuned to the frequency of said high frequency amplifier, and means including a circuit fedvvith said interfering and static energy for actuating saidauxiliary rectifier.

3. A radio receiver in accordance With claim 1 and having a delay circuit interposed between said filter and said main high frequency amplier `and an auxiliary ,amplifier in the last said means.

VIVIAN COHEN HENRIQUEZ. BERNARDUS DOMINICUS HUBERTUS TELLEGEN.

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