ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR WIDE RANGE TUNING METHODS AND TECHNIQUES APPLICABLE TO SEARCH RECEIVERS QUARTERLY PROGRESS REPORT NO. 10, TASK ORDER NO. EDG-4 Period Covering October 1, 1953 to December 31, 1953 Electronic Defense Group Department of Electrical Engineering By: L. W. Orr Approved by:,/i LJaw I. L. Beavis R. Bradley H. W. Welch, Jr. H. Diamond Assoc. Prof. of Elec. Engrg. M. Winsnes Supervisor, Electronic Defense Group Project 1970 CONTRACT NO. DA-36-039 sc-15358 SIGNAL CORPS, DEPARTMENT OF THE ARMY DEPARTMENT OF ARMY PROJECT NO. 3-99-04-042 SIGNAL CORPS PROJECT 29-194B-0 January 1954

TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS iii ABSTRACT iv 1. PURPOSE 1 2. PUBLICATIONS AND REPORTS 1 3. FACTUAL DATA 1 3.1 Use of Ferromagnetic and Ferroelectric Materials in the Tuning of RF Components 1 3.1.1 Ferromagnetic Materials Study 1 3.1.1.1 Magnetic Core Tests in the 1 - 10 Megacycle Range 1 3.1.1.2 Magnetic Core Tests in the 100 Megacycle Range 2 3.1.2 Ferroelectric Materials Study 2 3.1.2.1 Hysteresis in Pure Barium Titanate 2 3.1.2.2 Barkhausen Noise Measurements in Ferroelectric Specimens 3 3.1.3 Applications of Ferroelectric Materials 8 3.1.3.1 Electric Tuned High Frequency Oscillators 8 3.1.3.2 The Use of the Temperature-Epsilon Surface in Electric Tuned Oscillator 12 3.1.3.3 Negative Capacity Element 15 3.2 Investigation of Techniques for Signal Detection and Frequency Determination 15 3.2.1 Voltage Tunable Magnetrons 15 4. CONCLUSIONS 17 5. PROGRAM FOR NEXT INTERVAL 17 5.1 Ferromagnetic and Ferroelectric Tuning 17 5.2 Voltage Tunable Magnetron 17 DISTRIBUTION LIST 18 ii

LIST OF ILLUSTRATIONS Fig. No. Page 1 Hysteresis in Barium Titanate Crystal 4 2 Epsilon Surface for Aerovox "Hi-Q" Body 40 at 26~C 5 3. Attenuation Characteristics of Filters for Barkhausen Noise Equipment 6 4. Gate Generator and Gated Amplifier Circuit for Barkhausen Noise Equipment 7 5 Low Capacity Stack 9 6 Ultra - Audion Oscillator 11 7 Epsilon-Temperature Surface for Aerovox Hi-Q 41 14 3 High Voltage Regulator Circuit for Magnetron 16 iii

ABSTRACT This report reviews the progress of the Electronic Defense Group on Task Order EDG-4, for the quarter ending December 31, 1953. Tests have begun on magnetic cores produced under Task 6 to determine their suitability for magnetic tuning. Equipment for quantitative Barkhausen noise measurement in ferroelectric specimens is nearing completion, and is discussed briefly. Several VHF oscillator circuits have been investigated for dielectric tuning and the results are summarized. Power supplies and test equipment for the magnetron program are nearing completion. iv

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN WIDE RANGE TUNING METHODS AND TECHNIQUES APPLICABLE TO SEARCH RECEIVERS QUARTERLY PROGRESS REPORT NO. 10, TASK ORDER NO. EDG-4 Period Covering October 1, 1953 to December 31, 1953 1. PURPOSE The purpose of this report is to summarize the progress made by the Electronic Defense Group in the Study of wide-range tuning methods and techniques applicable to search receivers during the last quarter of 1953. 2. PUBLICATIONS AND REPORTS Mr. H. Diamond attended the Rutgers University symposium on ferroelectric ceramics on November 14. He also visited the Bell Telephone Laboratories in Murray Hill, New Jersey. Mr. H. Diamond and Dr. L. W. Orr visited the Glenco Corporation, Metuchen, New Jersey, on December 15, 1953 to discuss the manufacture of special ceramic capacitors for ferroelectric tuning. 3. FACTUAL DATA 3.1 Use of Ferromagnetic and Ferroelectric Materials in the Tuning of RF Components 3.1.1 Ferromagnetic Materials Study (L. W. Orr and L. C. Beavis) 3.1.1.1 Magnetic Core Tests in the 1 - 10 Megacycle Range. For magnetic tuning, a magnetic core must have reasonable values of Q and an adequate variation of

ENGINEERING RESEARCH INSTITUTE - UNIVERSITY OF MICHIGAN permeability with the application of modest values of control field. Because many cores have a rather low value of Q (less than 3) in certain frequency ranges a method of low Q measurement was worked out. Because of certain instrumentation difficulties, this method is not yet on a production testing basis. 3.1.1.2 Magnetic Core Tests in the 100 Megacycle Range. A set of cores produced by Task 6 having composition similar to Ferramic E showed some indication of usefulness in this VHF region. By varying the firing schedule, different properties were obtained in various members of the set. Cores fired at low temperature tend to have moderate losses, low permeability and very little change in permeability with applied field. This is due to the fact that crystal growth is very small and permeability arises almost entirely from domain rotation rather than from wall motion. Cores fired at higher temperatures tend to have excessively high losses at VHF because of wall motion effects and wall resonance, higher permeability, and larger change in permeability with applied field. A testing schedule has been established for this set of cores. The one core tested to date (Type A-34-1) does not appear to be suitable for VHF tuning. When it was subject to a dc control field which varied from zero to 30 oersteds, (150 ampere turns on one inch OD core), the variation in permeability at 100 megacycles was barely perceptible. Under these conditions the Q varied from 6.0 at zero to 6.8 at 30 oersteds of control field. 3.1.2 Ferroelectric Materials Study. 3.1.2.1 Hysteresis in Pure Barium Titanate. (H. Diamond and L. W. Orr) Several specimens of pure crystaline barium titanate were kindly furnished by the Bell Telephone Laboratories, Murray Hill, New Jersey. Hysteresis loops were obtained on these specimens giving first hand information regarding temperature and loading effects. It was found, for example, that electrodes of silver paint loaded 2

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN the surfaces of the crystal so that unnaturally fat P-E loops were produced. It was necessary to use very thin vacuum-deposited silver electrodes to avoid these loading errors. Specimens were plated in vacuum equipment in the RandallLaborat - tory of Physics. Hysteresis loops for a 6 mil thick specimen of C-oriented barium titinate are shown in Fig. 1. It is quite rectangular at room temperature (Fig. la), but shows a double loop1 above its Curie temperature (Fig. lb). The circuit used to plot these loops is very similar to that previously reported.2 3.1.2.2 Barkhausen Noise Measurements in Ferroelectric Specimens. (M. Winsnes) To study the Barkhausen noise in ferroelectric specimens, an analyzer is being constructed as shown by the block diagram, Fig. 2. A sinusoidal field is applied to the specimen by means of the high-voltage transformer and low-pass filter which give at least 70 db rejection of line transients and other noise above 5 kc. The high-pass filter passes the Barkhausen noise, but offers at least 70 db rejection of all power and noise voltage components below 10 kc. Attenuation characteristics of these filters are shown in Fig. 3. Since the Barkhausen noise varies in a cyclic manner, depending upon the phase of the applied cyclic field,3 a sampling technique is required in making quantitative measurements. The block shown as "Noise Measuring Equipment in Fig. 2 will consist of six sub-units as follows: (a) Gate Generator, (b) Gated Amplifier, (c) Thermocouple, (d) Chopper, (e) Tuned Amplifier and (f) Detector and Meter Indicator. Figure 4 shows the circuit of the Gate Generator and Gated Amplifier. This equipment permits the measurement of the noise energy over any desired small portion of the 60 cycle wave. This is performed by taking a small This was reported by W. J. Merz, Phys. Rev., V. 91, p. 513 (1953). 2Quarterly Progress Report No. 9, Task Order No. EDG-4, Fig. 2, Electronic Defense Group, Univ. of Mich., October 1953. 3 op. cit., footnote 2, Fig. 6, p. 13. Ir.'..3

'~ -O-'3Pf 91,- ~d-V OZ61 (a) AT 25~C. (b) AT 115 C. FIG. I HYSTERESIS IN BARIUM TITANATE CRYSTAL. 4

~9-Z-01 IW3P 9*b-S-V OL6-f HIGH LOW SPECIMEN HIGH LOW | VOLTAGE PASS HOLDER PASS NOISE -- XFMR I FILTER FILTER PREAMP. 60^llovT~~~~~~~~~~~ I II NOISE MEAS.. EQUIPMENT CRO FIG. 2 BLOCK DIAGRAM OF BARKHAUSEN NOISE ANALYSING EQUIPMENT. 5

*gc-II-z 1i3r zg-bs-B Oz61'd b —-- 0 0 0 0 0 N (1D 0 0 cl: 4 Z oo - o >- Lw N - a: Q cr wro L n / 0 0 o 0 ____'S w I.- L 0 O o: L.\J o~ --- o - 0 nL/ 0..0 a: ~~~~~~~____ __^~~~~~~~~~__ Or Nis 6 -J^0 J N (L ~ 0-J 0 *w- q p - 6qp ~~~~~~~~~~~~C0J b (0 0 0 0 —6

0 0O~( )I D w LLI > a. a. o X,oo oa lo L m~nN lo ID olI ( on o~~~~~~~~~~~~~~~~~~~~~~~~o.,o ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ a w I~~~~~~~~~~~~~~~~~~~~~~~o 5-T~~~~~~~~~~~~r R1~~~~~~~~~~R 131 I I c~~~ A QN oO n 3e~~~~~~~~~~~o w ScD~~~~w >~~~~~~~~~~~~~u 0~~~~~~ oI a:~~~~~~~~~~~Q o o~~~~~~~~~~~~~~~~~~' - r~~~~~~~~~~~~~~~~Q at gI\Nh > IN o:,~,u ( o O o 04~~~~~~~ nl on~~~~~~~~~~~~~~ 0 n 1 <

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN sample of the noise from each cycle and averaging the result. To identify the phase position of the sample, a portion of the sampling gate voltage is used to intensify the trace on the oscilloscope. Construction of these units is nearing completion. Several methods of squaring and metering the gated noise have been tried which proved unsatisfactory because of insufficient sensitivity or instability. The present method using a thermocouple appears to be satisfactory, and no major problems are anticipated. 3.1.3 Applications of Ferroelectric Materials. 3.1.3.1 Electric Tuned High Frequency Oscillators. (H. Diamond) A survey of various lumped-constant oscillator circuits suitable for electric tuning in the HF and VHF ranges is being made. Breadboard models were constructed in each case, and representative results to date are shown in Table I. TABLE I Representative Results on Electric Tuned HF Oscillators Freq. Range FM* Range of Capacitive Type of Tube me % Bias Field Circuit Oscillator Type gm volts/mil Element ** Circuit /Lmhos 50 - 100 100 0 - 100 A Harley 6AH6 11,000 95 - 115 21 0 - 60 B Push-pull 6J6 5,300 ll0 - 140 27 0 - 60 B Colpitts 6J4 12,000 135 - 160 18.5 10 - 60 B Push-pull 6J6 5,300 365 - 375 2.7 0 - 60 B Ultra-audion 6J4 12,000 * The per cent FM expresses the increase in frequency above the lowest frequency as a percent of the lowest frequency. ** Capacitive circuit element A consisted of two 120OL f Glenco K3300 capacitors in series across the tank. Element B consisted of a stack of six 200 uuf Glenco K3300 capacitors connected in series as shown in Fig. 5. 8

9S-ll-Z W3r tL-LO-V u. 61 R R X RRC'vv~, )A R NOTE: +0 DC CONTROL VOLTAGE - R 5 MEG. 6l = CERAMIC CAPACITOR FIG. 5 LOW CAPACITY STACK. 9

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN This arrangement permits application of the full polarizing voltage to each capacitor, but offers the desired low capacity (approx. 33~,zLf) for the tank circuit. This device was used because low value capacitors were not available in materials suitable for electric tuning. Special capacitors of low value made with thin dielectric are now on order. With thin dielectric it is possible to obtain the required polarizing field with reasonable values of applied voltage. The condition for oscillation in a Colpitts circuit may be shown to be approximately gm >' 4 X + (1) where gm is the effective tube transconductance Q the total Q of the resonant circuit C and L the capacity and inductance of the resonant tank and G the input conductance of the grid and grid circuit exclusive of the tank. For other oscillator circuits, the condition for oscillation has the same general form as relation (1). Because the Q of ferroelectric capacitors is greatly reduced at HF and VHF, it is necessary to use tubes of high transconductance, and tank circuits of large L/C ratio for successful operation in this frequency region. Some of these circuits refuse to oscillate at VHF because of this reduced Q. However, as the electric field is applied to the ceramic, the Q is often improved sufficiently to permit oscillations. It has been observed while varying the field about the point where oscillations begin that the starting field (value at which oscillations start) is larger than the dropout field. The highest frequency so far observed in lumped-constant electric tuned oscillators was with the ultra-audion circuit shown in Fig. 6. The inductive I See for instance Quarterly Progress Report No. 8, Task EDG-4, Fig. 5, Electronic Defense Group, University of Michigan, July 1953, p. 8. 10

tS-01-Z Vw3r "~-1.3-V OZ61 B+ RFC RF BY-PASS 4J^ — + RESONANT CONTROL C a -- TA N K VOLTAGE 6J4 Rg p C 47K> 0_ (a) ACTUAL CIRCUIT i - ^P^Cgp^ f Cpk Cgk (b) EQUIVALENT CIRCUIT FIG. 6 ULTRA-AUDION OSCILLATOR. 11

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN part of the tank circuit is composed entirely of the grid and plate leads L, while the variable capacitive e&ement C is used to vary the resonant frequency of the tank. At resonance we find the relation Cw2L (2) C C' where C' C + Cgk * Cpk Cgk + Cpk By differentiation it follows that Sw 1 ~LCc' C - LC(C+ C' (3) or dw _ - Ct dC w - 2(C + C') C (4) which shows that C should be kept small in relation to C' to obtain the best frequency shift. 3.1.3.2 The Use of the Temperature-Epsilon Surface in Electric Tuned Oscillator Design. (L. W. Orr) The tuning of an electric tuned oscillator is done by changing the electric field applied to the tank capacitors. The ratio of maximum to minimum capacity must be the square of the required frequency ratio. It is desired to have a relatively small control field for the desired frequency range. At the same time the temperature coefficient of capacitance should be kept at a minimum. Given a particular material and tuning ratio, the correct operating temperature and required control field are to be determined. An example shows how the T- surface may be employed to simplify this design problem.:12

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN Example: Find the operating temperature and required control field for an electric tuned oscillator of frequency ratio 1.5 to 1 using capacitive elements of Aerovox Hi-Q 41. The T-E surface for this material is shown in Fig. 7. At any given value of field the small circles indicate the maximum capacity, and hence the temperature at which the temperature coefficient is zero. It may be seen that as the electric field increases, the zero point temperature also increases. Thus it is not possible to obtain a zero temperature coefficient over the entire tuning range. The solution is shown by the heavy dashed lines in Fig. 4. A temperature of 46 C is chosen, which is slightly higher than the zero point temperature for zero field. The curve for this temperature is followed as the field is increased until one obtains a capacity ratio of (1.5)2 or 2.25. This is obtained at a field of 10.4 kilovolts per cm. It is seen from the surface that at this field the zero point temperature is slightly higher than 46~C. Therefore, at the minimum capacity there is a small positive temperature coefficient, and at the maximum capacity (zero field) there is a small negative temperature coefficient. It is frequently desirable to have the zero temperature coefficient at the mid-frequency. The tuning ratio for mid-frequency is 1.25, and therefore, the capacity ratio for this point is (1.25)2 or 1.562. On our curve for 46~C we find that this capacity ratio occurs at a field of 6 kv/cm as indicated by the dot-dash line. The temperature coefficient at this field and temperature is nearly zero. 13

~G-0-6 W3P ~~R-S-C 0OZ6-W'3q FOR AEROVOX HI-Q 41. 14

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN 3.1.3.3 Negative Capacity Element (L. W. Orr, L. Beavis and H. Diamond) The maximum range in dielectric tuning is limited by the ratio of maximum to minimum capacity available from a particular ferroelectric capacitor. Since this ratio is of the order of 8 or 9 for most useful materials, electric tuning cannot comp/ete in tuning range with ferromagnetic tuning in the MF range. However, if some method could be found to decrease both the maximum and minimum capacity of a ferroelectric capacitor by an equal amount, this ratio could be greatly increased. A negative capacity amplifierl may be used to perform this service. The input capacity of this amplifier is negative. If this negative capacity is placed in parallel with a ferroelectric capacitor of the proper value, it may be possible to make tuning elements which will compete with ferromagnetic tuning. The behavior of various negative capacity amplifiers over different frequency ranges will be studied to determine the feasibility of this technique. 3.2 Investigation of Techniques for Signal Detection and Frequency Determination 3.2.1 Voltage Tunable Magnetrons (R. Bradley) The study of the voltage tunable magnetron as a local oscillator for receiver use has been interrupted for the past several months while the equipment was in use for studies conducted under other tasks and Part II of this task was being completed (Part II was terminated last quarter). A second system is under construction which incorpo2 rates various features to overcome previous difficulties. To overcome magnetic FM produced by the 60-cycle heater current in the magnetron, a storage battery heater supply is employed. For closer and more accurate voltage control, the anode voltage regulator circuit has been redesigned. The construction of the regulator is now complete. (See Fig. 8). The new regulator furnishes currents 1 See for instance MIT Radiation Laboratory Series, Vol. 19, Appendix A, p. 767. 2See Quarterly Progress Report No. 6, Task EDG-4, Fig. 7, Jan. 1953, p. 15. 15

tfc-01- 0 W3P 0Z-10-8 O61 VV VI R3 0D3 0- y | O lOOK 330K i ----- IVOLTAGE I —-- 4000 VDC ADJUST REGULATED UNREGULATED OUTPUT INPUT R5 R7 200K 100K V4 RI R2 OC3 20K 20K M2 R8 IOOK VS OC3 TI R9 Ia~ ~~~ __ _ _ _ J 1 _ __ ^O OK 3v3~~~~~00 RIO IOOK OC3 RESISTORS TUBES RII-R29 V8-V26 21 0 VOLTAGE R30!K f\ ADJUST I lOOK V27 OC3 — o22 FIG. 8 HIGH VOLTAGE REGULATOR CIRCUIT FOR MAGNETRON. 16

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN up to 35 ma with good regulation, and can be adjusted for any voltage from 600 volts to 2700 volts. 4. CONCLUSIONS In spite of the expected delay in the research programs caused by the major move to the North Campus, the major objectives for the period have been accomplished. 5. PROGRAM FOR NEXT INTERVAL 5.1 Ferromagnetic and Ferroelectric Tuning Solutions to the instrumentation problems will be sought in the low-Q measurements on ferrite cores, and a routine testing procedure will be established. The investigation of ferroelectric materials will continue, and further tests made of materials suitable for electric tuning including measurements of Barkhausen Noise. The negative capacity amplifier circuit will be investigated as a possible method of extending the frequency range of electric tuned oscillators. 5.2 Voltage Tunable Magnetron Construction of the new equipment will continue. The completed system will include power supplies, modulator, broad-band mixer, IF amplifiers, attenuators, and appropriate noise measuring equipment. Upon completion of the apparatus, the investigation program will begin. This will include noise figure measurements, and a study to indicate the effects of various parameters on noise figure in voltage tunable magnetrons. 17

DISTRIBUTION LIST 1 copy Director, Electronic Research Laboratory Stanford University Stanford, California Attn: Dean Fred Terman 1 copy Commanding Officer Signal Corps Electronic Warfare Center Fort Monmouth, New Jersey 1 copy Chief, Engineering and Technical Division Office of the Chief Signal Officer Department of the Army Washington 25, D. C. Attn: SIGGE-C 1 copy Chief, Plans and Operations Division Office of the Chief Signal Officer Washington 25, D. C. Attn: SIGOP-5 1 copy Countermeasures Laboratory Gilfillan Brothers, Inc. 1815 Venice Blvd. Los Angeles 6, California 1 copy Commanding Officer White Sands Signal Corps Agency White Sands Proving Ground Las Cruces, New Mexico Attn: SIGWS-CM 1 copy Signal.Corps Resident Engineer Electronic Defense Laboratory P. 0. Box 205 Mountain View, California Attn: F. W. Morris, Jr. 75 copies Transportation Officer, SCEL Evans Signal Laboratory Building No. 42, Belmar, New Jersey For - Signal Property Officer Inspect at Destination File No. 25052-PH-51-91(1443) 18

1 copy H. W. Welch, Jr. Engineering Research Institute University of Michigan Ann Arbor, Michigan 1 copy Document Room Willow Run Research Center University of Michigan Willow Run, Michigan 1 copy Engineering Research Institute Project File University of Michigan Ann Arbor, Michigan 11 copies Electronic Defense Group Project File University of Michigan Ann Arbor, Michigan 19

UNIVERSITY OF MICHIGAN 3 9015 03524 4493