US2317474A - Superregenerative receiver - Google Patents

Description

April 27, 1943. w. A. MONTGOMERY 2,317,474

SUPER-REGENERATIYE RECEIVER Filed June 6, 1941 Patented Apr. 27, 1943 UNITED STATES PATENT OFFICE SUPER-REGENERATIVE RECEIVER William Alan Montgomery, London, England, as-

signor to International Standard Electric Cor- V poration, New York, N. Y.

Application June 6, 1941', Serial No. 396,814 In Great Britain June 25, 1940 2 Claims.

(1) Id=A-B loge Vi where Id is the anode current Vi is the input voltage and A and B are constants This is known as the logarithmic mode of operation. In the linear mode of operation the detector is less sensitive but the output is directly proportional to the input instead of the logarithm of the input.

The chief distinction between the logarithmic and linear modes of operation is in the quench frequency. If the quench frequency is sufiiciently low to allow the oscillation to build up to saturation value before being quenched the detector behaves logarithmically. If, however, the frequency is increased until the oscillations are always quenched before reaching saturation value then the detector behaves linearly.

This invention is concerned with the superregenerative detector in its logarithmic mode of operation.

It will be shown in the following analysis that the audio frequency component of the output of such a detector is logarithmic, that. is, that the, output signal frequency amplitude is proportional to the logarithm of the modulating voltage of the incoming carrier wave. The magnitude of the harmonic distortion resulting from this particular kind of non-linearity is considered; it is shown that the distortion due to the logarithmic characteristic can be compensated by the use of a succeeding low-frequency amplifier having an exponential characteristic and that for complete correction a critical value of detector load impedance is necessary.

Now assuming that the quench frequency is much higher than the modulation frequency, and expressing Vi as a modulated carrier wave, thus (2) Vi=V(1+m cos wt) where m is the percentage modulation we obtain by substituting for V2 in Equation 1:

(3) Id=A--B loge V-B loge (1+m cos wt) The audio output is represented by the alternating components in the second part of this equation. It can be shown that this can be written in the form of an harmonic series as cos net 1 +41 m The only alternating current components of interest in the output are given by:

The fundamental component is given by:

The second harmonic is given by:

2 L E 2 +2 /1 m m etc. from which it can be seen that the distortion. in audio output is considerable particularly at high degrees of modulation. In order to eliminate this harmonic distortion the output is now'passed through an amplifier having an exponential characteristic such that:

(6) I a=Ke where Ia is the anode current Vg is the grid voltage If the resistance in the anode circuit of the super-regenerative detector is R2, the voltage; output is given by V2=R2'I.0.

If the fixed bias on the amplifying valve is Vi the grid voltage is given by:

2(1 +m cos wt) If the resistance in the anode circuit of the amplifying valve is R: the output voltage is given by:

2.m cos wt It will be seen'from this contains alternating current of the fundamental frequency only, and all the harmonics have been eliminated. There still remains a small amount of amplitude distortion which is in the nature of volume expansion. The degree of expansion is given by:

For degrees of modulation not greater than 70% this represents an expansion of little over 1 db. which is negligible.

Pentodes with fairly high negative bias form suitable amplifier valves for the present purpose. The Philips valve type E.452T has an exponential characteristic with grid bias voltages between 9 and -3.

The anode current of this valve is represented by Ia=28.7 e ma. when the anode voltage is 200 v. and the screen voltage is 100 v.

The anode current of a typical super-regenerative detector is given by:

(14) Id=6.8,45-.235 logm Vi ma. where Vi is the peak input voltage in microvolts. To obtain correction it has been shown that:

1 R'L-E With the numerical values given above 235.10 mhos.

that the output now v2. 2,317,474 whence: whence 50 Ri= 98 ohms. V2 =BRi 10g 2(1+m cos wt) A 1+1/1 If the anode load (R2) of the amplifying valve (9) I =K k(Vi+V is 100000 ohms and the standing bias on the a valve 4.3 v. the output voltage is given by: =K KVnklg Ia 1 0:? V. R. A. IS. 10 Log, =kV 1+\/1 m 2(1+ cos and at 30% mod. the audio output is: 1+ 1 -m 8.65 v. R. M. s. c0S and this output will be obtained for all inputs (11) M Kekv (my modulated to 30% irrespective of the signal strength. The fj' f; anpde g g g ggi Super 15 A super-regenerative receiver embodying the regenem We 8 Or Is so J invention and using the amplifier valve and im- IcBRi=1 pedance values given above by way of example is thus shown in the accompanying drawing.

1 The receiver comprises a super-regenerative 1? detector stagehaving a triode valve VI with a then tuned input circuit LI, Cl connected between grid 2(1 +1 cos t) and anode an intermediate point of this circuit .(12) I=AQL 1 +V1W' being at ground or cathode potential for high frequencies. A quenching voltage wave is applied across a condenser C2 which is inserted in series with a grid leak R3, whereby a pulse is applied to grid periodically to quench the oscillation after it has built up to saturation point.

The output of the detector valve is applied by resistance-capacity coupling RI, C3, R4 to the control-grid of a pentode amplifying valve V2. The connections to this valve are of well-known kind but the grid bias voltage is critically determined by suitable choice of resistance values in the potentiometer R5, R6, R1 to ensure that the valve operates over an exponential part of its grid characteristic.

What is claimed is:

1. A receiver of modulated carrier waves comprising a super-regenerative wave detector where- .in the quench frequency is sufiiciently low to allow the oscillation to build up to saturation value before being quenched followed by a low frequency amplifier the anode current of which is an exponent, of the grid voltage over the working range of grid voltages.

' 2. A receiver according to claim 1, wherein if the output current of the amplifier valve is expressed as Ke Vg being the amplifier input voltage, K and is being constants and if the detector anode current is expressed as AB loge Vi amps, Vi being the signal input voltage to the detector, A and B being constants, the detector anode-circuit load resistance has the approximate value of i Bk ohms.

WILLIAM ALAN MONTGOMERY.

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