1 A STUOY OF THE FEASIBILITY OF DESIGNING A SUPER-REGENERATIVE RECEIVER TO MEET CERTAIN CRITICAL RE~Urn.EMENTS Thaddeus Francis Kycia, B.Sc. A thesis submitted to the Faculty of Graduate Studies and Research, McGill University, in partial fulfilment of the requirements ror the degree of Master of Science. ABSTRACT A super-regenerative reeeiver has been designed for linear mode operation in a band from 455 Mc ./see. to 510 Me ./see. For 1inear mode operation it was neeessary to use automatie gain stabi1ization, whieh a1so kept the oscillator output pulses at a steady amplitude. The reeeiver was constructed, having a band-width of 630 Ke./see and a noise figure of 20 db. The experimenta1 resu1ts were in good agreement with the theoretiea1 estimates, and numerical values for eomparison are provided wherever possible. The reeeiver ean deteet a minimum signal of 1.5~volts, and it therefore IOOre than meets the sensitivity recpirements for use as a deteetor in a l.I.h.f. "bridge". ACKNOWLEOOEMENTS The writer wishes to express his appreciation to Dr. J.R. Whitehead who originated the project and under whose direction i t was carried out; to Dr. H. G.I. ivatson for allowing the use of his laboratory equipment and workshop, and to Mr. W. Avarlaid, Mr. B. Meunier, Mr. M. Kingsmill, and the staif of the Physics building for their kind cooperation. Special thank s are due to Dr. T. w. h. East for hi s frequent assistance and advice during both the project and the writing of this thesis. The writer is also indebted to the Defence Research Board, whose financial assistance made this work possible. FIGURES P~Gé 2.1 Block diagram of the super-regenerative receiver 13 3.1 The \.I.h.f. oscillator l' 3.2 Analagous lumped circuit of the .h.f. oscillator ~o 3.3 Plate current vs. grid bias voltage of the 5876 Jf 3.4 Transconductance vs. grid bias voltage of the 5876 2> 3.5 Determination of the gm cycle 3.6 Determination of the conductance cycle 3.7 Relative frequency response of the receiver '1 3.8 Noise band-width measurement 'J ~ 3.9 a) Output noise for no input signal " 3.9 b) Detected pulses which form the noise ." 3.10 a) Output for large input signal 37 3.10 b) Superimposed output pulses of equal amplitude 37 3.11 a) Output for an amplitude modu1ated input signal li 3.11 b) Formation of the sine wave "38 3.11 c) Relative separation of the pulses '3<1 3.11 d) Superimposed pulses for the waveform of fig. 3.11 a) 31 4.1 Frequency bridge of the quench oscillator ~I 4.2 The quench oscillator 4.3 \.I.h.f. detector and automatic gain stabilizer 4.4 The meter circuit 5.1 Receiver, front view 5.2 Receiver, back view 5.3 Receiver, bottom view (without shi~ld) 5.4 IIBridge" measurement setup CONTENTS 1. Introduction 1.1. Fistory of super-regenerative receivers. 1 1.2. Purpose of the receivers. g 2. Princip1es of Super-Regeneration 2.1. Super-regenerative action. II> 2.2. The conductance cycle. If) 2.3. Linear mode and a.g.s. Il 2.4. General description of the receiver. 12. 3. The Super-Regenerative Osci11ator 3.1. Construction of the oscillator. Ir 3.2. The 5876 penci1 triode. /1 3.3. The equivalent circuit of the plate càvity. 1'1 3.4. The graphical determination of a-. '-:1- 3.5. Theoretical formula for the output. !J.:J 3.6. Super-regenerative band-width. '30 3.7. Noise figure. '3~ 3.8. Oscillograms of oscillator output pulses. '31' 4. Other Sections which constitute the Receiver 4.1. Quehch osci1lator. 4.2. The u.h.f. detector and a.g.s. system. 4.3. The mater circuit. 5. Construction and Use of the Receiver 5.1 The 1ayout and operation of the receiver. 5.2 The super-regenerative receiver as a "bridge" detector. tI? Summary and Conclusions Appendix 1. References '7 1. INTRODUCTICN . 1.1 History of Super-regenerat1va receivars The principle of the super-regenerati va osci1lator Was first introduced by E.H. Armstrong in 1922. Its high gain 1fas reallzed, but its other remark­ able features were ovar100ked and i t was on1y thirteen yeaxs later that turther investigation was pursued into the subject. H. Ataka, 1935; M.G. Scroggie, 1936 and F.W. Frink, 1938 published papers exp1aining the pheno­ menon of super-regeneration. Lt about the SaIlle time severa1 unique circuits, making use of super-regeneration, appeared in print. W.B. Lewis and C.J.!. M.ilner (1936) designed a duplex operation trans­ ceivar (simu1taneous two wsy cOImnUnication) by mald.ng use of the reradiating properties inherent in the super-regenerative osci1lator. It acted alterna­ t!valy as a receiver and transmi tter during each quench periode Each trans­ ceiver would be sensitive to in-coming pulses at that specifie time when the signal pulse just arrivad from the other transceiver. S. Becker and L.M. Leeds (1936) described a two w~ police radio system. This radio installation consisted of duplex operation trom headquarters to eaeh car and simplex operation between the cars. The reeeiver had a com­ bination of both the super-regenerative and superheterodyne princip1es and the resultant sensitivity was more than sufficient to fUlfillthe rigorous requirements. The super-regenerative circuit then found its w~ into numerous radio amateur receivers, as weIl as the "walkie talld.e" developed by the U.S. A.r'tlJy Signal Corps and later modified for use during the Seoond World War. It bad the desired features of baing sensitive, light, simple and economioal. Other contributors who promoted the understanding of super-regenerati"f9 theory were W.E. Bradley (1948); A. Hazelti"s; D. Richman and B.D. Lo\l..ghlin (1948); Macfarlane and Whitehead (1946, 1948); H.A. G1uckSlD;Bll (1949) and L. Riebmann (1949). The super-regenerative receiver became we11 known for its part in the wartime I.F.F. (identification friend or f'oe) Mark 111 responder, deve10ped at T.R.E. in Great Brita1n. The purpose of' the I.F.F. responder was to indicate to an observer at a radar station whether soma distant aircrait Was t'riandly. The respondar on the a1lied aircrait wou1d amplif'y the re­ ceived radar pulses and reradiate them. Theae were picked up by the radar station and observed as long traces on the P.P.I. screen, compared to the small dots which represented the refleoted pulses t'rom an enemy aircraf't. The use of' a.g.s. (automatic gain stabilization) was made in these respon­ ders and this gave them the added f'eature of good stabi1ity over a wide t'requency range (157-lS7Mc./sec.). More than 200,000 of' these t'ully auto­ matic responders were produced to be fi tted into al1 the allied ships and planes as a joint effort by the United states and Great Britain. "Super-Regenerative Receivers" by J.R. Whitehead (1950) describes the circui t of' the Mark 111 responder, as wall as ma.ny other circuits making use of' the super-regenerative principle. The book a1so contains a comprehen­ sive treatment of' super-regenerative theory as we11 as physical interpre­ tation of' the resu1ts. Another major piece of work published after that time on super-regen­ erative theory was by HeA. Whee1er in the form of two monographs on the analysis of super-regenerative selectiv1ty.and design f'ormulas. 1.2 Purpose of the receiver The o~ect of' the work undertaken was to stuQy the feasibi1ity of a super-regenerative receiver operating in the Unear mode at 500Mc./sec., with specific properties which could make it use able as a "bridge" detector. " It would 'he used as a null indicator for a General Radio admittance me ter • The specifications are that it would be able to detect IO/f'\t of signal or better and that it would have a sufficient amount of stability. The par­ ticular receiver discussed here cao detect 1.5;'f'V: of signal and achieves its very reliable operation through the use of the automatic gain stabili­ zation. The purpose of the a.g.s. is to keep the receiver in the linear mode of operation, thus adding to the complexi ty of the receiver. On the whole, however, it is much simpler than a superheterodyne operating at the srune trequency. /0 2. PRINCIPLE OF SUPER-REGENERATION 2.1 Super-regenerativa aotion A parallel tuned circuit can maintain oscillations if enough energr is supplied te it te overcome the resistiva losses. If, at a.ny time, more energy is supplied than dissipated, the oscillations will grow. A. positive feedbaek amplifier, which may consist of one tube, can be made to supply the nacessary energy. The condition that oscillations be maintained is that the transconductance of the tube equa.l a certain value which depends on the losses in the circuit. The transconductance is a function of both the plata voltage and grid bia.s voltage. By periodical1y varying ei ther ·of the se , one can get tœ tube into a s tata where the oscil­ lations grow, or wbere they decay. The general practice is to modulate the grid bias voltage with the output of a quench oscillator whose waveform, for simplici ty, is sinusoidal. Over part of the quench cycle the grid bias is very negative and no oscillations existe The grid then becomes Iess œga• tive until it reaches the grid bias voltage, which is just necessary for os­ cillations to existe The osoillations begin to grow as the bias becomes still less negativa, until they reach a peak in amplitude which comes at a time wben the grid bias returns to its critieal.