US2345511A - Regenerative detector circuit - Google Patents

Description

Patented Mar. 28, 1944 2,345,511 REGENERATIVE s'rno'ron on ourr Harry E. Thomas, Haddonfield, N. J., assignor-to Radio Corporation of America, a corporation of Delaware pplicat o c m e 30, 9 erial 70 54 7 Claims.

The present invention relates to a regenerative detector circuit and more particularly to a detector circuit of this type provided with auto.- matically compensated feed-back coupling means and which is capable also of being used eificiently in multi-band receivers.

Because of their simplicity and low cost, radio receivers of the tuned radio frequency type are desirable in certain fields of use. In order to increase the sensitivity and the signal-to-noise ratio of such receivers, it is known to employ a triode, tetrode or a pentode tube as a regenerative detector; Such receivers are frequently employed, depending upon the degree of regeneration, for' the reception of code or c. w. (continuous wave) signals or of voice modulated signals. For telegraph reception, suflicient radio frequency energy in the output circuit of the detector is fed back into the grid circuit'to produce oscillations which heterodyne with the incoming signal. However, with the detector regenerative, that is, with feed-back taking place but not enoughto cause oscillation, voice modulated signals may be received with considerably greater strength'than when the detector is in a non-regenerative condition. The sensitivity of the regenerative detector is greatest when the tube is oscillating very weakly, in beat-note reception, or when very near the oscillation point but not actually oscillating, in the reception of telephone or voice signals. In order to obtain the adjustment vfor greater sensi tiVity it iscustomary to provide a regeneration control.

There are various known forms of regenerae tive detectors but they have certain disadvantages and are not readily adaptable for use in multi-band receivers. For example, in one particular circuit that has been used to some extent and to which reference will be made hereinafter, it is necessary, in switching from one band to another, to switch in the appropriate one of a plurality of feed-back windings. It is necessary also to set the regeneration control for the different frequencies in each band due to changes in the gain and ieedeback with frequency. In addition there are spurious responses caused by theYieed-back coil resonances and the expense of additional windings and aswitch.

It is therefore the main object of my invention to provide an improved regenerative detee e u t h c .wi a o th ab ve and other disadvantages. i

A er Object s o p evieeeutomaticelly compensated cou ling a eeh re ive det c in. rder o ehtain ee isteh en iti ity eve e iven frequency heed- Other ob ect o th i vent n a e he. p e en ral the s mplicit an see y f n at e detec ors or use he ..:'P? re eivers.

Th nov r stores ch acteri i f my h vention a set ier h with par icula ity in the appended la ms! The en h e thewe e w both a to its r an zat on and mo e fe eretime o eth r with fur her o je ts ehd ad na e ther o will best be un er ood b efe ence to t e fo w ng deserih take in seenection with the accompanying drawing in which Fig. 1 illustrates a known regenerative deector used a mulFi-bhhd recei r an F fe- 2 s. a re enera ive cleteet eirelht em e y e e pres nt in ntion.- 7

Referrin rst to F g. 1 c he dr w the receiv oi the e ie er is shown e u at ve pur ses to he a thr -ben receiver, a t n:

elude preseleete s stem. shewndia rammati cell by th block end re ene ative de ete circu t h h includes he a e 2.- e re leetor i clude n or mo e r d equehey amplifiers. inc mi signals ei ed t he in put thereei from he an enna 3 or othe s na co lector. The amhlihee s e e gna requeney ap ea in i th Q p-ht 4 9 the Pressle tor s tran mitte to thesisn nt ol id 5 of t e d tect r ube wh c ma he a sc ee ri r a sense tube th ehe ne e the intersteee couplin r hsiermers o T1 end n upon the .ir qhehe b n d i ed t he rece ed hich .is eet rmih si by th t q DI the switch membe s and he e e P mar s .6 to eithe qll hg t an me s ha their l w potent al Il$ e hhe t t a condu or 9 whi h through th fil er const uted b h resist r l a s the c n en r H leads to h +15 te m na o su ta e s u ce o w The hi h potential nds oi the P ima es e m n te n th w tc c ntact w h. whieh th sw h, me be S1 is ada ted to select ely. eehteet- The t ee former secondaries i? to ill have their low poent a ends 0I1h9$ to the ground d nduc r 1.5, their es eet high P tent a ends t rminatin in the w h contac s t wh ch th swi h memb r e is .eda t si 9 se eetivel e 1- tact. A var able on e s r U i eeh ee ed tween the rid side o the .Se a d g ound and forms w th an one th trehs erme seeonearies H to 4. ete mi es by e p s ion lective connection to the cathode 2| of the tube i of one of a plurality of windings 22 to 24 which are coupled respectively to the secondaryor grid windings I2 to M in proper phase. The cathode or feed-back windings have'their low potential ends connected to a common lead l5 which is grounded, their other ends terminating in contacts with which the switch member S3 isadapted to selectively contact. The switch mernbers S1 to S3 and one or more others that may be included in the preselector are actuated in unison and constitute the band switch which determines by its position of adjustment the particular frequency band being received.

The output 25 of-the detector includes a plate load resistor 26 connected between the +3 terminal of the power supply andthe plate electrode 21, a coupling condenser 28 being connected from the plate side of the load resistor for transmitting the detected signals to the audio amplifier and utilization device, not shown. A variable tap 23 on the potentiometer 39 serves to supply voltage to the screen grid 3i. The condenser 32 is a high frequency by-pass condenser for screen grid currents.

Briefiy the operation of the regenerative detector is as follows: v

' With the band switch set in the position shown in'the figure to receive signals in the band determined by the transformer T1, the tuning condenser H5 is adjusted to tune the secondary ii! of said'transformer to a desired frequency within the selected band. The signal frequency impressed on the control grid 5 is then rectified by the method known as grid-circuit rectification, the rectified or detected signal in amplified form appearing in the output or plate circuit 25. Radio frequency currents of the signal frequency are also present in the plate and screen grid circuits, and since the cathode coil 22 is included in these circuits, some of the high frequency energy will be fed back to the input circuit due to the coupling between the coils 22 and I2. The regeneration is controlled by adjustment of the tap 29 to vary the screengrid voltage.

As pointed out previously the system above described is subject to the-disadvantage that each time the receiver is adjusted to a new frequency, whether in the same or difi'erent band, it is necessary to adjust the regeneration control for most efiicient operation. For example, if the receiver is tuned anew to a certain signal which happens to be of a different signal strength than that to Whichthe receiver was previously tuned, unless the regeneration control is properly adjusted the detector circuit will regenerate eithertoo weakly or too strongly.- r

In Fig. 2 of the drawing there is disclosed a re- -generative detector-circuit according to the invention designed to overcome the above and other disadvantages previously mentioned- The circuit of Fig. 2 is in many respects like that of Fig.1, except as noted hereinafter, similar o'r corresponding elements in both figures being represented by the same reference charand also to provide grid bias.

acter. The cathode or feed-back coils employed in Fig. l are omitted in the circuit of Fig. 2. Instead the cathode return is connected by way of the lead 33 to the common lead I5 to which are connected the low potential ends of the several transformer secondaries l2 to M. Between the lead 33 and ground there is connected a network which comprises a condenser C..and an inductance L connected in series. A resistor R is shunted across the series combination of L and C-and serves to complete the cathode D. C. path The above network it will be noted is connected between cathode and ground, and being included in both the grid and plate circuits of the detector tube 2, it serves as'the feed-back coupling means between the plate and grid circuits. A variable condenser 34 is mechanically coupled and movable with the tuning condenser 16 and is connected to lead 33 and ground thereby shunting the coupling network C, L and R.

Theseries combination. of L and.() is chosen series resonant below the range of tuning of the several bands, so that the effective inductance of this combination becomesless as frequency decreases. This tends to make regeneration inadequate at lower frequencies of the band. However, the capacity 34 becomes greater as the circuit is tuned to lower frequencies, and the er" fective inductance of the entire network of L,

C and 34 can thus caused to decrease, increase, or remainconstant with decreasing frequency according to the amount of capacity of 34 at each frequency adjustment. It will be seen that'a 35 capacity variation curve for 34 canthu'sbe chosen such that the amount of regeneration will be automatically maintained at an optimum value throughout the range of tuning forany given band.

The variablecondenser 34 serves therefore to control the regeneration automatically. Except for changes necessary when going from band to band, the regeneration controlby adjustment of the tap 29 of the screen voltage is unnecessary since feed-back and regeneration are nearly constant over the individual frequency ranges.

While I have shown and described certain preferred embodiments of the'invention, it willibe understood by those skilled in the art that modifications and changes maybe made without departing from the spirit and scope of the invention. 'WhatIclaim is. j 1'. A'regenerative detector comprising anfelectron discharge tube provided with at least a cathode, a signal control grid and an anode, an input circuit having its inductance connected between signal grid and cathode and its variable. capacitor connected between the grid end of theinductance and ground, and a feedback'network connected between the cathode end of the inductance and round.

2. A regenerative detector asdefined in claim 1 wherein the feedback networkcomprises a fixed combination of resistance, capacitance and inductance. V j I 3. Aregenerative detector as defined in claim 1 wherein the feedback network comprises a fixed combination of resistanca capacitance and inductance and a variable capacitor adjustable with the variable capacitor of the input circuit connected across the feedback network. I

4. A regenerative detector comprising an electron discharge tube provided with at least a cathode, a signal control grid and an anode,-a network providing regenerative feedback from the output to the input circuit of said tube connected between cathode and ground and included in both the grid to cathode and anode to cathode circuits, and a variable capacitor shunted across said feedback network for controlling regeneration.

5. A regenerative detector adapted for use in a multi-band receiver comprising an electron discharge tube provided with at least a cathode, a signal control grid and an anode, a network operating in each of the bands providing regenerative feedback from the output to the input circuit of said tube, said network being connected between cathode and ground and included in both the grid to cathode and anode to cathode circuits, and a variable capacitor shunted across the network for controlling regeneration.

6. A regenerative detector as defined in claim 5 wherein the feedback network comprises a series connected capacitor and inductance which offer a substantially constant impedance to the feedback energy over a wide band of frequencies.

7. A regenerative detector comprising an electron discharge tube provided with at least a cathode, a signal control grid and an anode, a resonant input circuit tunable over a range of frequencies connected between said control grid and cathode and including an inductance and a variable capacitor effectively connected in parallel, and a feedback network connected between the cathode end of the inductance and ground and which is included also in the plate to cathode output circuit.

HARRY E. THOMAS.

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