INVESTIGATION OF METHODS FOR MEASURING THE EQUIVALENT ELECTRICAL PARAMETERS OF QUARTZ CRYSTALS. PROGRESS RENT. NO. 4, 16 JAN-1 JUNE 57. (CONTRACT DA 36-039-SC-71191).

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• Document Page Count: 39
• Document Creation Date: December 27, 2016
• Document Release Date: October 31, 2013
• Sequence Number: 1
• Publication Date: April 29, 1958
• Content Type: REPORT

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ENGINEERING EXPERIMENT STATION
of the Georgia Institute of Technology
Atlanta, Georgia
PRCGRESS REPORT NO. 4
PROJECT NO. A-271
INVESTIGATION OF METHODS FOR MEASURING THE
EQUIVALENT ELECTRICAL PARAMETERS OF QUARTZ CRYSTALS
By
DOUGLAS W. ROBERTSON, S. M. WITT, JR. and WIUUD4( R. FREI
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CONTRACT NO. Dtk-56-059-sc-71191
DEPARTMENT OF THE ARMY PROJECT NO. 5-24-02-072
SIGNAL CORPS PROJECT NO. 8673
-? 0 0 0 0
16 JANUARY 1957 TO 1 JUNE 1957
PLACED BY THE U. S. ARMY
SIGNAL CORPS ENGINZARING LABORATORIES
FORT MONMOUTH, NEW JERSEY
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Progress Report No. 41 Project No. A-271
TABLE OF CONTENTS .
I. PURPOSE
II. ABSTRACT
III. CONFERENCES AND PUBLICATIONS
IV. INTRODUCTION .
V. EXPERIMENTAL WORK AND CIRCUIT STUDIES
1 A. Crystal Measurements Standard
3 1. Introduction
2. Impedance Calibrations
5 3. Experimental Crystal Measurement Data
4. Theoretical Crystal Studies
B. Power Measurements
1. Introduction
2. Prototype Power Meter
3. R-F Power Measurements
C. Experimental CI Meter
1. Coaxial Crystal Parameter Bridge
2. Experimental Oscillators
VI. CONCLUSICNS
VII. PROGRAM FOR NEXT QUARTER
VIII. PERSONNEL
IX. APPENDIX
A. Addendum
B. Admittance Characteristics of Measured Crystals
This report contains 66 pages.
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Progress Report No. 4, Project No. A-271
LIST OF FIGURES
1. ImpedLnce Calibration neasurement Setup
2. Comparison of Vae.ous Methods of Line Length Substractions
3. Bridge Measurements of 100-Ohm Termination
4. Bridge Measurc-nents of 200-Ohm Termination
5.
Page
6
9
11
12
15
17
20
Admittance Meta* Measurements of. 100-Ohm Termination
6. Present Laboratory Measurements Standard Setup
7. Crystal Holder Characteristics of Crystal. No. Ft-116
8. Holder Equivalent Circuit for Crystal No. Ft-116 21
9. Characteristics of Crystal No. Fs;116 at 245 M2/sec 23
10. Rectangular Admittance Plot of Characteristizs of Crystal No. Ft-116
at 245 MC/sec
11.
24
Asaumed Equivalent Circuit of Crystal No. 7a-?1A
at 245 Mc/sec . . ._25
12. Thermistor Bridge Pover Measuring System 27
13. r....ctotype Power Meter 30
14. Prototype Power Meter Schematic 31
15. R-F Power Measurements 33
16. Ambient Temperature Variations of One and Two Thermistor Configura-
tions 35
17. Ambient Temperature Variations of Prototype Bridge 36
18. Capacitance Bridge Oscillator 44
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Provess Report No. 4, Project No. A-271
LIST OF APPENDIX FIGURES
Page
A-1 . Admittance Characteristics of Crystal No. Ft-57 52
A-2 . Admittance Characteristics of Crystal No. Fa-59 53
A-3 . Admittance Characteristics of Crystal No. Fa-89 54
A-4 . Admittance Characteristics of Crystal No. Fa-91 55
A-5 . Admittance Characteristics of Crystal No. Ft-92 56
A-6 . Admittance Characteristics of Crystal No. Ft-1003 57
A-7 . Admittance Characteristics of Crystal No. Fa-104 58
A-8 . Admittance Characteristics of Crystal No. Fa-105 59
A-9 . Admittance Characteristics of Crystal No. Fa-116 60
A-10. Admittance Characteristics of Crystal No. Fa-117 61
A-11. Admittance Characteristics of Crystal No. Ft-118 62
A-12. Admittance Characteristics of Crystal No. Fa-82 63
A-13. Admittance Characteristics of Crystal No. n-83 64
A-14. Admittance Characteristics of Crystal No. Fa-40 65
A-15. Admittance Characteristics of Crystal No. Fa-44 66
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Progress Report No. 4, Project No. A-271
LIST OF TABLES
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Page
I. COMPARISON BETWEEN MEASUREMENTS OBTAINED WITH THE STANDARD
SYSTEM AND MEASUREMENTS SUPPLIED PI USASEL 18
II. COAXIAL CRYSTAL PARAMETER BRIEGE MEASUREMENTS 39
III. CHECK OF BaircE REPEATABILITY 40
IV. CHECK OF BRIDGE SYMMETRY 41
V. CRYSTALS OPERATED IN CAPACITIVE BRIEGE OSCILLATOR 46
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Progress Report No. le, Project No. A-2/1
I. PURPOSE
The purpose of this project is threefold:
1. To study and investigate methods and techniques for measuring the
equivalent electrical parameters of quartz crystal units in the frequency
range of 150 to 300 mc/a, including:
(a) A means for directly measuring the power drive of a crystal
unit,
(b) A simple and practical mesas of cancelling the capacitance of
the crystal unit, Co, at the test frequency, and
(c) A means of measuring the effective resistance of the crystal
unit at the series resonant condition.
2. To accumulate data from the investigations of 1. above, with a view
of utilizing the information for the development of a practical test method
for the frequency range 150 to 500 mc/s which viii make it possible to:
(a) Subject the crystal to any selected drive level between the
limits of 0.2 and 4.0 milliwatts,
(b) Measure crystal resistance values between the limits of 20 and
200 obms,
(c) Attain an accuracy of resistance measurement of t5 ohms or .110
per cent, whichever is greater, and
(d) Attain an accuracy of resonant frequency determination within
-0.001 per cent of the series resonant frequency of the crystal
unit.
3. To study and investigate means for eatablishing a laboratory measuring
technique to be used as a standard for measuring the equivtlent electrical pa-
rameters of quartz crystal units in the frequency range of 100 to 500 mc/sec.
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Progress Report No. it, Project No. A-2/
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II. ABSTRACT
Further investigations of the calibration of various commercially avail-
able instruments for use with the Laboratory Standard Crystal Measurements
System were conducted. None of the particular -.154,trizments which were investi-
gated were sufficiently accurate for one percent overall accuracy.
A developmental system vas used to obtain several admittance circle dia-
grams for each of 15 high frequency crystals over the frequency range frcm 140
to 455 me/see. The data were compared with measurements from other sources.
Initial investigations of the equivalent circuits of high frequency cry-
stals based on the data from the Measurements Standard indicated that the pre-
sently used equivalent circuit. does not entirely account for the crystal's be-
havior. This investigation did not progress sufficiently to provide definite
conclusions.
A prototype thermiator-Lridge power meter for mea. ring the r-f power
dissipated in VHF quartz crystals was constructed and tested. Comparative
measurements indicated the unit to be capable of measuring r-f power from 0.5
to 4.0 mw with an accuracy of 5 percent.
Impedance measurements made with the Coaxial Crystal Parameter Bridge in ?
a passive arrangement indicated the bridge accuracy to be comperable with that
of other available methods.
An experimental UHF capacitance bridge oscillator was Constructed that
displayed characteristIcs suitable for use with the coaxial bridge. Crystal
controlled oscillations as high as 420 mc/sec were obtained with a modified
version of this oscillator.
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Progress Report No. 4t 11ct No. A-271
III. CONFERENCES AND PUBLICATIONS
W. W. B. Wrigley, Mr. D. W. Robertson and Mr. S. N. Witt, Jr. attended
s conference at USASEL on March 18, 1957. The technical status of this project
and the future courses of action were discussed. The immediate objectives as
outlined under Chapter VI, *Program for Next Quarter," were agreed upon.
A paper entitled "Quartz Crystals Above 200 Megulv-'..es" VAS presented by
Mr. S. N. Witt, Jr. at the Atlanta Section meeting of the Institute of Radio
Engineers on April 26, 1957. A paper entitled "Crystal Measuring Techniques
Above 200 Me/sec" was presented by Mr. S. N. Witt, Jr. at the Eleventh Annual
Frequency Control Symposium held in Asbury Paric, New Jersey, on May 9, 1957.
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Prefress Report No. 4, Prolect No. A-271
IV. INTRODUCTION
This rept actually covers an extended period of reduced activity for
the 4-1/2-month period from 15 January 1957 to 1 June 1957. This extension,
requested by USASEL, resulted from administrative delays in negotiating a
12-mcnth extension of the present contract. It is expected that support for
full effort will again be applied in July 1957.
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Progress Report No. 4, Project No. A-271
V. D:PERIMENTAL WORK AND CIRCUIT STUDIES
A. Crystal Measurements Standard
1. Introduction
During this period, only a portion of the phases of development of
the Crystal Measurements Standard were continued. The subsections previously
titled "Stable Signal Generators," "Power Measurements," and "Detector Systems"
are not included in this report since data previously reported indicated that
the signal generator presently in use waz% satisfactory for immediate project
needs and since further advancement in the study of power measurements and
detector systems will require the purchase of vsricus maditional pieces of com-
mercial equipment.
Principal efforts were directed toward investigations of calibration ac-
curacies of various devices in current use. This study was greatly facilitated
by the use of a large scale digital computer. The conclusion from this study
is that the impedance and admittance bridges in current use do not provide suf-
ficient accuracy to fulfill the purpose of the project. This, however, does
not necessarily iMply that the types of instruments involved are not satis-
factory since the particular instruments which were used had been subjected
to mistreatments of various kinds. Conclusions as to the potential accuracy
of each instrument must await the purchase of new equipment.
Many crystal measurement runs were made on newly arrived crystals. Some
of these meftsurtments were compared with measurements obtained from ether
instruments. These measurements are, of course, subject to the calibration
errors of the instruments used.
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Progress Report No. 4, Project No. A-2/1
Some theoretical studies were made concerning the appropriate choice of
equivalent electrical circuits for quartz crystals. These studies made use of
laboratory measurements on various high frequency crystals. They were con-
ducted primarily to determine the ability of the present measurements system
to provide useful information about the quartz crystals.
2. Impedance Calibrations
Efforts to establish the sources and magnitudes of instrument errors
were continued. In particula:*, large amounts of data were obtained on the
Hewlett-Packard Model 803A VHF Bridge and the General Radio Type 1602-B Admit-
tance Meter. These data consist of measurements made on General Radio 50-,
100-, and 200-ohm terminations which are assumea to be accurate tc within one
percent for impedance magnitude. ComTarisons were made on the assumption that
the impedance values of these terminations are exact.
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A typical measuremeric setup is shown in Figure 1. The frequency calibration
SIGNAL
GENERATOR
BRirGE
DETECTOR
WRIABLE
LENGTH LINE
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Figure 1. Impedance Calibration Measurement Setup.
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or the Signal Generator was generally found to be satisfactory without the use
of a frequency meter since no high-Q resonant elements are Involved in the set-
up. The Variable Length Line consisted of assorted combinations of fixed-
length air-dielectric transmission lines (General Radio) and in sum cases iz.
eluded a constant-impedance adjustable line. Amplitude modulation of the sig- -
nal source was sometimes employed to obtain greater useable detector sensitiv-
ity. This was also possible because of the absence of high-Q resonant ele-
ments in the setup. General Radio Type 8/4 connectors with "Cliplocks" were
used in making coaxial connections wherever possible. Care was taken to reduce
direct signal leakage between instruments to a minimum by minimizing non-criti-
cal line lengths and employing solid coaxial cable wherever possible.
Sourccs of errors wnicn yeze discussed in the previous progress report are:
a. human errors in reading the bridges,
t. errors caused by poor null indication,
c. drift in the bridge, terminations or other elements with time,
d. errors in calibration of the terminations,
e. errors inherent in the methods of applying corrections to the
readings, and
f. errors in bridge calibration.
Item e was the first of these sources of errors that was more fully inves-
tigated during this report pertod. Since impedance measurements were made for
arbitrary lengths of transmieEion line, it was necessary to make one or more
short-circuit measurements and then subtract the short-circuit impedance from
the readings obtained when using the termination. Of the variaa-possible
methods of subtraction, the one making use of Z-0 charts or Smith charts
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Progress Report No. le Project No. A-271
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appeared to be most attractive because of the relatively small amount of time
required. However, repetitive reduction of the same data yielded results dif-
fering by more than one percent in sore cases. Mathematical subtraction of
the short-circuit-impedance using a alide rule was next attempted with a simi-
lar magnitude of disagreement resulting in the final impedance values. TO ob-
tain neater accuracy, a desk calculator and a set of mathematical tables.vere
next employed. This combination was highly subject to human mistakes. The
mistakes resulted primarily from the complexity of the computations. The
equation which had to. be solved was
z_ Z
Sc
where Zt is the impedance of the termination to be .calculated from a bridge
reading,
Z is the short-cilcuit bridge reading,
sc
Z is the bridge reading with the termination in place, and
Zo is the characteristic impedance of the transmission line.
Some of these quantities are complex impedances, thus adding to the
culties already inherent in making the calculations.
Since satisfactory agreements were never obtained among the methods
diffi-
of
short-circuit subtractions discussed above, the computations were performed on.
Remington Rand ERA 1101 Univac Computer. Typical results obtained using the
various computation method.3 are illustrated by Figure 2. It can be seen that
the desk calculator calculations were sufficiently accurate, providing mistakes
could be eliminated; however, this process war very time consuming, requiring
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Progress Report No. le, Project No. A-271
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approximately 15 hours of time to subtract the short circuit for 20 points with
the likelihood of appreciable errors remaining in 20 percent of the final so-
lutions. The computer provided 0.01 percent accuracy with no mistakes in 43
seconds of computation time. Typical total computer time included 5 to 7
minutes program loading time plus 1 to 1.5 minutes per set of 20 readings for
loading and computation. Fifteen to thirty minutes of personnel time were re-
quired for preparing the data for each set of 20 readings. The initial prepa-
ration of the computer program, however, required in excess of 20 hours of
personnel time.
The use of the digital computer completely eliminated the errors inherent
In the methods of applying corrections to the readings.
Figure 3 shows a graphical slmlnry of the data obtained when using a par-
ticular HP Model 803A VHF Bridge to measure the impedance of a OR 100-ch m termi-
nation. Two of the curves show the data obtained by applying corrections for
line length only. The third curve presents data which were fully corrected by
applying the correction curves supplied with the bridge. These curves correspond
to the curves of Figure 13 of Progress Report No. 5 except that the line length 4
subtraction was performed by the computer for the current presentation. Some
improvement in accuracy, especially for the phase angle, was obtained by the
application of the correction curves provided with the bridge.
Figure 4 presents similar curves obtained by replacing the 100-ohm termi-
nation with a GR 200-ohm termination. An appreciable improvement in accuracy
was obtained, in ,:?,10 m-Ammpic, ty msing the correction curves provided with the
bridge. These curves correspond to Figure 14 of Progress Report No. 3.
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Progreso Report No. 44_Project No. A-271
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Other data indicated that errors ce?scd by poor null indication and errors
due to drift were compartively small for the previously presented data. Errors
due to poor null indication may, however, become appreciable when AK modulation
of the signal source cannot be used. Thus the errors indicated in Figures 3
and 4 may be associated with (1) human errors in reading the bridge, (2) errors
in calibration of the terminations, crid (3) errors in bridge calibration. The
first and third errors may be appropriately grouped as "bridge errors.TM. If
the errors in calibration of the terminations can be considered to be zero,
the data presented in Figures 3 and 4 indicate that the oarticular VHF bridge
can be specified to be accurate to within 7 percent for impedance magnitude
and within - 6 degreed for phase angle with full corrections applied and for
the particular impedances and lire lengths involved. Other data indicate that
approximately the same accuracy can be obtained for any impedance with a magni-
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a tude between 50- and 200-ohms and for e line length except lengths which ap-
proach odd multiples of one-quarter wavelength. The accuracy may be specified
X
to be 9.5 percent for impedance magnitude and - 20 degrees for phase angle when
to
the computer is not used for short-circuit subtractions and when The coryections
supplied with the bridge are not applied.
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Another Ii? Model 803A VHF Bridge was briefly investigated and was found
to
to have slightly poorer accuracy. Bcth of these bridges had been in use for
?v4
several years and had not always received the proper treatment. This model
of bridge has been improved by the manufacturer in recent years; thus, current.
production models may show appreciable improvement in accuracy over the par-
ticular instruments which were available to the project. Tentative plans are
being made to either have one of the old bridges rebuilt or to purchase a new
8
instrument for similar evaluation.
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The General Radio Type 1602-B Admittance Meter was al.zo subjected to in-
tensive laboratory investigations. Runs Were made using 50-, 100-, and 200-
ohm terminations separated from the instrument terminals by transmission line
lengths of 0, 10, 20, 30, Ito, and 50 cm. The computer program was -modified to
perform admittance subtractions based on short-circuit admittance readings.
The difference in length of 0.6 cm between the short-circuit and the termina-
tions was not included in the corrections; however, this distance would modi-
ty the results only slightly. If the instrument accuracy were greater, Llae
correction for this distance would become more important. Figure 5 shows a
graphical summary of the data obtained by usi,,c, the 100-ohm termination. Near
points where the line length api:rcached one-quarter wavelength, large errors
were to be expected. Disregarding these regions, however, the accuracy of the
instrument can be specified in most cases to be within 15 percent for impedance
magnitude. The curves show that the accuracy is generally greater for the
shorter line lengths. For example, the maximum error in impedance magnitude
for the 0-cm line length is 7.5 percent. The computer data gave phase angle
accuracies within - 15 degrees in most cases and s.noximum error of 6 degrees
4-1
for the 0-cm line length. This data is not presented graphically. Because
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-of the large errors observed for the 100-ohm termination, it was felt that the
use of the computer was not warranted for correcting the 50- and 200-ohm data.
When the Admittance Meter is used with a half--zavelength line both magnitude
and phase angle errors are greatly reduced (typicmlly less than 5 percent ma&.
nituae error and less than - 4 degrees phase angle error).
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This particular Admittance Neter had been in use for several years and
had received very rough treatment which probably accounts for much of the
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Progress Report No. 4,... Project No. A-271
error. Tentative plans are also being made to obtain a new Admittance Neter
for evaluation.
It was concluded that the instruments presently in use do not even ap-
proach the accuracy required to satisfy the rurpose of the project. The data
indicate, however, that new instruments, if given special care in calibration,
ma, be capable of providing the necessary accuracy. The possibility of includ-
ing calibration data for a particular instrument in the computer program has
also been suggested. Ac applied to crystal measurements, this would mean that
the data obtained from the VHF Bridge or Admittance Meter would be placed into
the computer and the resulting output would be the fully corrected impedance
characteristics.
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Progress Report No. 4, Project No. A-271
The admittance characteristics of these crystals are shown in Figures A?a.
through A-15 of the Appendix. Only the principal responses at each overtone
are shown except
for Figure A-15 where the frequency separations between the
SIGNAL
ArMaTTANCE
XIXER
LOCAL
GENERATOR
NETER
RECTIFIER
OSCILLATOR
MARCONI
GR TrPE
GR TYPE
HP MOD.
TYPE 1066/1
'
1602
874 )02
608A
FREQUENCY
ADJUST-
NULL
3. Experimental Crystal Measurement Data
METER
ABLE
tETECTOR
BERKEIE1
LINE
GR TfPE
Experimental data were obtained on a series of 15 high frequency quartz
MOM 5570
1216A
crystals supplied by the USASEL. Complete circle diagrams were obtained for
the principal response at each overtone frequency between the frequency limits
.of 140 and 455 me/sec for each crystal.
grams is shown in Figure 6. This setup
The setup used for obtaining the dia-
is identical to that presented in Fig-
ure 2 of Progress Report No. 3. Although the previous section indicated that
the VHF Bridge may at present be made more accurate than the Admittance Meter,
the Admittance Mater was chosen for the crystal measurements because of its
requirement of less null detection sensitivity. A half-wavelength line was
used for each measurement to obtain greater accuracy and so that line length
subtractions would not be required. In all, 76 circle diagrams were obtained
for the 15 crystal units. This number does not include the many minor re-
sponses (spurious) which were also obtained.
-16-
- - ?
V.
Y -COMPONENT MOUNT
Ficrurr- 6. Present Laboratory Measurements Standard Setup.
principal responses and the spurious responses were very small. The numbers
near each overtone response indicate respectively the overtone number and the
approximate frequency of the response in mc/sec. The resonant frequency at
each response is considered to be the frequency at the point of maximum con-
ductance. This Is the resonant frequency that would be obtained if cancel-
lation coils were used to antiresonate the effective Co of the crystal. The
equivalent resiFtance is considered to be the reciprocal of the maximum
?17-
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Declassified in Part - Sanitized Copy Approved for Release
4 .01
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? - ?????" '"?????ftwin
?
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.21PIEITILk2s21.112.11$12111,1s2LIIL_Ln_L
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conductance. The reader is cautioned, however, that this method of Co cancel-
of the
does not
crystal.
necebc...eily yield the rca.....ant frequency of the motional arm
This aspect is discussed in the next section of this report.
a
Table I shows a comparison between the resonant resistance and frequency
obtained from the curves of Figures A-1 to A-15 and the corresponding data sup-
plied by USASEL as obtained by using a Crystal Impedance Meter. The values of
TAME I
COMPARISON BETWM TE.A2URaiENTS OBTAINED WITH THE STANDARD
SnIEM AND MEASUREMMTS SUPPLIED BY USASEL.
Standard Measurement System
Data from USASEL
Co
Crystal No.
Frequency
Rczistance
Freouency
Resistance
Fa-57
(mc/sec)
144.997890
(ohms)
58
(mc/sec)
(ohms)
60
(Tad)144.996591
7.1
Fa-59
144.995210
34
144.994504
38
6.6
Fa-89
154.969630
38
154.969724
38
5.8
Fa-91
155.025300
31
155.024304
32
5.8
Fa-92
154.983520
54
154.982208
35
5.8
Fa-103
165.010510
34
165.010252
36
6.4
Fa-104
164.965530
43
164.9614807
42
6.0
Fa-105
164.950250
38
164.949722
37
5.9
Fa-116
175.029820
34
175.029814
, 36
4.8
Fa-117
174.899000
36
174.898072
33
5.7
Fa-118
174.896970
42
174.896575
39
5.8
Fa-82
168.944740
69
188.944609
70
6.1
Fa-83
188.996630
109
188.996369
102
4.4
Fa-40
195.979000
123
195.978463
106
6.0
Fa-44
196.013340
69
196.013830
-,
63
8.1
-18-
/OP
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vallanb.
Progress Report No. 4, Projeet No. A-271
Co as obtained by USASEL are also included. The effective Co as determined by
the Measurements Standard may be readily calculated by considering the value
of the susceptance at the point of maximum conductance.
The maximum disagreement between resistance values is 14 percent. With
two exceptions, the values agree within 9 percent and for 8 Measurements the
agreement is within 5 percent. In all cases, the frequencies agree to %;ithin
better than 0.001 percent. In 3 cases, the frequency agreement is better than
0.0001 percent. The resistance disagreements do not appear to be related to
the frequency disagreements except for the Crystal No. Fa-40 where the disa-
greements are large for both frequency and resistance. It is possible that
the characteristics of this crystal may have changed somewhat between inter-
vening measurements.
4. Theoretical Crystal Studies
One of the 15 crystals whose admittance characteristics are presentea
in the Appendix was examined in gr_tte. detail to determine the validity of
the conventionally assumed equivalent electrical circuit. These studies and
conclusions, while necessary to determine the usefulness of the Crystal Meas-
urements Standard, bre nevertheless subject to errors introduced by the pres-
ent limited accuracy of the system. The particular crystal chosen for these
studies was Crystal No. Fa-116 whose circle diagrams are shown in Figure A-9
of the Appendix.
The holder characteristic of Crystal No. Fa-116 was first determined.
This was accomplished by using the measuAment setup of Figure 6 for the fre-
quency range from 100 to 1000 mc/sec. The holder characteristic is plotted in
Figure 7. The small circles represent the regions where crystal overtone
-
??? ?
-19-
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Declassified in Part - Sanitized Copy Approved for Release
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0'?'"41: gel.--*Iffr
ese....1???????.?
Progress Report No. 4, Project No. A-271
Figure 7.
Crystal Holder Characteristics of Crystal No. Fa-116.
-20-
41???? - ?
1
1
^
Progress Report No. 4, Project No. A-271
responses have a tendency to produce erroneous readings. The numbers near
the small circles indicate the overtone number of the crystal response occ
ring in this region. The 21st through 29th overtone responses, all of whic
were appreciable and rather broad, made accurate readings difficult to obta
at frequencies above about 700 me/sec. This situation was aggrviated even
more by the signal source instability at these freluencies (the crystal ov
tone respontes r.t. the higher frequencies have not been plotted due to this
stability). The large circle in the figure was chcsen as the eir,?le which
best represented the complete holder characteristic. It may be observed t.
this circle is not centered about the zero susceptance axis. This indicate.
the need for an additional shunt capacitence, Co.', as a part of the holder
equivalent circuit which is shown in Figure 8. The element values appeari.:
In Figure 8 are the values calculated from the half-power points on the circ
diaLram of Figure 7. The value of (Co Co') was also measured at 400 ke/s
and found to be 4.6 ??fd.
Figure 8. Holder Equivalent Circuit for Crystal No. Fa-116.
-21-
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?
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?
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436
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A,..... r
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Progress Report No. 4, Project No. A-271
The fact that the measured points on the holder characteristic follow an
elliptical path indicated a slight nonlinearity of element values with fre-
quency. However, this nonlinearity appears to be negligible. The elliptical
shape may, moreover, be due entirely to measurement errors.
The crystal response at 245 me/set was chosen for detaifed study. The
measured points and the resulting circle approximation are described by Figure
9. Figure 10 presents the corresponding rectangular plot of the measured
points. The assumed equivalent circuit of the crystal is shown in Figure 11.
The resonant frequency of the crystal's motional arm could not be readily de-
termined from the curves of Figures 9 and 10; however, the circle diagram of
the motional arm was obtained by successive subtraction of the holder elements
using admittance and impedance Smith charts. The shunt element, Co', was first
removed by displacing the circle as shown in Figure 9. The circle was next
transferred to an impedance Smith chars (not shown) where LL and RL were re-
moved. The circle was then transferred back to rgure 9 where Co was removed
as indicated. As would be epectcti, the center of the circle fell very nearly
on the conductive axis. This fact, however, does not by itself substantiate the
correctness of the assumed equivalent circuit. Various freauency points must
also be investigated. For example, if the motional arm circle of Figure 9 is
correct, its resonance must lie at the point F. If this point is traced back
to the complete crystal disf;ram ty use of the Smith chart transformations, it
will occupy the various positions indicated. If the point, Fo, is trans-
ferred to Figure 10, it will not occupy the anticipated position. Time was
not available before the preparation of this report to determine whether or
not this is the normal frequency shift accompanying an impedance transformation.
-22-
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??????????m?????....????????ar
..........mr?????????
Progress Report No. 4, Project No. A-271
??
s"
???
???
?A ?1
MOTIONS. ARM PLUS C.
COMPLETE CRYSTAL
.Figure 9. Characteristics of Crystal No. Fa-116 at 245 Mc/sec.
-23-
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ii/11,Wtra:
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50-Yr2013/10/31 :CIA-RDP81-01043R002300080001-3
1
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*weer re" 1???li..."01,:?????6
Progress Report No. 4, Project No. A-271
t
I
u..
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m
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dt
,
o
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Progrcss Report No. 4, Project No. A:2/k
If it is not, it is probable that .theeventual explanation will result in the
adoption of at ::lternate equivalent circuit.
0
C '
o
R1 1
????????
Figure 11. Assumed Equivalent Circuit of Crystal No. Fa-116 at 245 Mc/see.
The element values for the equivalent circuit of the crystal's motional
arm may also be determined by tracing the half-power bandwidth points, Tb,
through the Smith charts to Figure 10, where the frequencies can be read from
the curve. All natural and derived crystal parameters can then be calculated.
For example, the Qo of the motional arm was found to be 36,000. It :11 inter-
esting to observe that the Q of the complete crystal unit with reactive cancel-
lation may be calculated as 34,000 from Figure 10. It may also be observed
from this figure that the most desirable reactive cancellation coil for this
crystal unit would be one with a susceptance of 9 millimhos corresponding to
an inductance of 0.07 ?h. This corresponds to an assumed (Co + C0') of 5.85
?"fd, which, results in a crystal resonant frequency of 245.01426 mc/sec com-
.pared to the resonant frequency o* the motional arm of 245.0450 mc/sec. This
-25-
Ilm?????????
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Declassified in Part - Sanitized Co .y Approved for Release
1.! ?
50-Yr 2013/10/31: CIA-RDP81-01043R002300080001-3
.????,????????? ?????????
Progress Report No. 4, Project No. A-271
raises the question as to which frequency should be the baais for the specifi-
cation of the crystal's parameters.
Although the above development did not progress sufficiently to provide
definite conclusions, it did indicate the need for further study of the equiv-
alent circuit of quartz crystals at high frequencies. It is probable that
additional investigations will offer satisfactory explanations for some of the
observations which have been.cited ur that errors may be found which will in-
validate the results presented.
B. Power Measurements
1. Introduction
The equivalent electrical parameters of quartz crystals are to a
varying extent a function of the crystal power dissipation, and it is therefore
necessary to measure and specify the power level at which the pt-rameters are
measured. A power measuring ievice which is compatible with the developmental
parameter measuring instrumentation should exhibit the following characteris-
tics: (1) sufficient sensitivity to measure r-f power in the range from 0.2
to 4.o mw, (2) the ability to measure r-f power over the frequency range from
150 to 300 mc/sec, (3) the ability to rr.,asure power without any electrical
connection between the dissipating body and the power measuring device, and
(4) the ability to measure the power dissipation of the crystal without ac-
cess to the interior of the hermetically sealed can of the crystal unit.
A thermistor bridge r-f power measuring system of the type shown in Fig-
ure 12 shows the most promise of satisfying the above requirements. Presently
available thermistors and null indicators make possible a system which is
capable of exhibiting a sensitivity in excess of that necessary to measure
-26-
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???0,?????1?C: ?????Vt? P
1111
1111?11Ed ?
Progress Report No. 4, Project No. A-2T1
the power levels of interest. However, ambient temperature variations limit
the degree to which this sensitivity can be practically utilized. The sensi-
tivity of the system Is limited by the maximum bridge unbalance indications
which are caused by ambient temperature variations. These indications must be
less than the allowable error of the minimum power level to be measured. The
use of two thermistors in the bridge reduces the errors due to ambient tempera-
ture variations considerably, and makes possible the nore effective utiliza-
tion of the maximum sensitivity of the bridge-
s'411)
Figure 12. Thermistor Bridge Power Measuring System.
-27-
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Declassified in Part - Sanitized Copy Approved for Release
50-Yr 2013/1 0/31 : CIA-RDP81-01043R002300080001-3
AP:417r
-
Progress Report No. 4, Project No. A-271
?????
The two thermistors, shown as T1 and TA on Figure 12, are mounted on the
re.Astive elements of two rheostats, R1 and R2, and are connected as adjacent
arms of a wheatstone bridge. The bridge is balanced by adjusting the bridge
balance potentiometer, R5. The r-f power to be measured is applied to Rheo-
stat R1' causing the temperature of the rheostat to increase. ? This temperature
fncrease is coupled to thermistor T1 and causes a decrease in the resistance
of the thermistor. This decrease in the resistance of T1 causes an unbalance
in the bridge. Applying d-c power to the second rheostat, R2, causes the tem-
perature uf R2 and T2 to increase which in tses decreases the resistance of T2.
When the decrease in the resistance of T2 is equal to the decrease in resist-
ance of T the bridge will again be balanced. Under thee conditions, the d-c
power applied to R2 will be equal to the r-f poker applied to RI, provided the
two rheostat-thermistor combinatiOns are identical. Any errors introduced by
differences in the two combinations may be easily determined by applying a known
d-c power to R1 and adjusting the d-c power applied to R2 until the bridge is
balanced. Any difference between the known d-c power into RI and the d-c power
applied to R2 represents the error due to differences in she two rheostat-ther-
mistor combinations. Therefore, this difference between the two d-c powers
may be used as a correction factor for the total system error.
The procedure described above makes possible ..he measurement of r-f power
dissipation in a rheostat without any electrical connection between the rheo-
stat and the power measuring instrument, thereby eliminating any possibili'y
of the power measuring instrument altering the operation of the system contain-
ing the dissipating loody.
-28-
??????????
r???????? 1??????????? ??????=???????????????????
Progress Report No. 4, Project No. A-271
The quartz slab of a conventiosal crystal unit is encased in a hermettcal-
ly sealed can and it is impractical to insert a heat sensing element into the
can of each crystal unit to be measured. If Ri is the rheostat of the Crystal
Parameter Bridge or the test resistor used in the CI Meter substitution system,
the r-f power df.ssipated in the rheostat will be equal to the r-f power dissi-
pated in the crystal. Therefore, measurement of the power dissipated in the
rheostat as described above, is equivalent to measurement of the power dissi-
pated in the quartz crystal.
2. Prototype Power Meter
A prototype thermistor-bridge power meter for use in measuring the r-f
power dissipated in VHF quartz crystals was constructed and tested. Figure 13
shows the prototype power meter connected to a Coaxial Crystal Parameter Bridge.
A Minneapolis-Honeywell, Model 104WIG, Electronik Null Indicator is used as the ?
null detector and a Marconi Type 1066/1 Signal Generator is shown connected as
the r-f power source. A schematic diagram of the prototype power meter is shown
in Figure 14. Two type 32CH1 Glennite Thermistors, shown as 71 and T2 on the
schematic, were connected as adjacent arms of the bridge. The-thermistors were
bonded to the resistive films of two VHF Rheostats so that the temperature of
the resistive films determines-the temperature and, hence, the resistance of the
thermistors. This bond was made with Sauereisen High Temperature Cement No. P-7
Robertson, D.W., Scott, T.R. and Wrigley, W.B., Investigation of Methods for
Measuring' the Esuivalent Electrical Parameters of Quartz Crystals. Final Report,
Contract No. DA-56-039-sc-56730, Georgia Institute of Technology, Atlanta, May
31, 1956, 11-31.
. ?
-29-
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Declassified in Part - Sanitized Copy Approved for Release
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50-Yr 2013/10/31: CIA-RDP81-01043R002300080001-3
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Progreso Report No. 4, Project No. A-271
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????????.
??? Parr. J.
Progress Report No. 4, Project No. A-271
which :exhibits good heat conductivity and good electrical insulation. The test
rheostat, shown as R1 on the schematic, is normally operated as the bridge rheo-
stat in the Crystal Parameter Bridge or as the test resistor in the CI Meter
substitution system. If the resistance of the test rheostat is equal to the
S1 R7
HELIPOT 21K 1( R locoG
ELECTRONIK
81 41c 45%1 10T-10K 3300 1.6K NULL INDICATOR
R3
HELI POT
10T
5 5K
3300 1.6K
Figure 14.. Prototype Power Meter Schematic.
-31-
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
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Progress Report No. 4, Project No. 1-271
?
series resonant resistance of the quartz crystal under test and if the frequency 4
is equal to the series resonant frequency of the crystal, the power dissipated
in the test rheostat is equal to the power dissipated in the crystal. The ref-
erence rheostat, R2, is mechanically connected to R1 to minimize ambient tem-
perature variation effects. EI-C power controlled by R6 .ind metered by is
dissipated in /12.
The thermistor bridge is initially balanced with no power applied to the
rheostats by adjusting P5 with the bridge d-c power on. The r-f power to be
measured is then applied to R1. The heat generated in Ri causes the resistance
of thermistor T1 to decrease, unbalancing the bridge. Di-C reference power is
then applied to R2 and adjusted by R6 until the bridge is again balanced. The
d-c power necessary to obtain this balance is real on 111. This reference power,
when corrected for system errors is equivalent to the r-f power in RI and, hence,
to the r-f power dissipated in the crystal.
3. R-F Power Reasurements
In order to calibrate the pover meter, specific amounts of d-c power
ranging from 0.5 mw to 4.0 taw were applied to the test rheostat, R. The bridge
was rebalanced by anplying d-c reference power to the reference rheostat, R2.
The results are plotted as the d-c calibration curve of Figure 15. This curve
represents the system error.
A Hewlett-Packard, Model 608C, VHF Signal Generator was used to apply spe-
cific amounts of r-f power, at 16 me/sec, ranging from 0.5 mw to 4.0 mm, to R1.
The bridge vas reblanced by applying d-c reference power to R2. The curve ob-
ttined from these r-f power readirgp is also shown in Figure 15 for comparison
with the d-c calibration curve. The r-f power applied to the test rheostat was
calculated from the HP Signal Generator attenuator dial reading.
-32-
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Progress Report No. 4, Project No. 1-271
LI
LU
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 :CIA-RDP81-01043R002300080001-3
??1
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4
Progress Report No. 4, Project No. A-271
In order to check the accuracy of the signal generator attenuator and as
an additional check on the thermistor-bridge power meter, voltage measurements
were made across the test rhecstat with a Hewlett-Packard, Model 410B, Vacuum
'Dube Voltmeter and the signal generator output was measured with an Empire
Devices, Model NF 105, Noise and Fie1d Strength Meter. Results from these
measurements are plotted on Figure 15 for comparison with the d-c power neces-
bary in R2 to balance the thermistor bridge. Figure 15 does not give a true
indtPation of the accuracy of the instruments compared because the power .values
were calculated by squaring the voltage readings obtained from the instruments
and, therefore, the errors shown on the power curves are approximately twice
the errors of the instruments. Hence, all three curves are within the accuracy
claimed for the inbtruments involved.
Since the curve obtained With the Hewlett-Packard VHF Signal Generator
lies approximately midway between the curves obtained with the voltmeter and
field strength meter, the r-f powers calculated from the signal generator at-
tenuator dial readings were taken as correct values of r-f power. With this
assumption, a comparison between the d-c calibration curve and the HP VHF Sig-
nal Generator curve indicated that the prototype R-F Power Meter should be
capable of measuring r-f pcwer In the range from 0.5 mw to 4.0 mw with an ac-
curacy of 5 percent.
Several termination type commercial r-f power meters appear to be suffi-
ciently accurate for use in checking the prototype power meter. An attcmpt is
being made to procure one or mcre of these units in order to further evaluate
the accuracy of tht- thermistor bridge.
-34-
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ce
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20
1.5
1.0
0.5
Progress Report No. h, Project No. A-271
ONE THERMISTOR
-0.5
-1.0
5 10 15 20
TIME
Figure 16. Ambient Temperature Variation:. of One and Two
Thermistor Configurations.
-35-
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25
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Progress Report No. 4, Project No. A-271
?????????? ??? ? ?C ..? .? Oft :At@ la
In order to scertain the improvement in useable bridge sensitivity ob-
tained with two matched thermistors, tests were made over 30-minute periods
with one-thermistor and two-thermistor bridge configurations. The recults of
these tests, as shown in Figure 16, indicated that the.maximum error due to
ambient temperature variations in the two-thermistor bridge was less than 2
percent of the
the errors due
two-thermistor
maximum per iota
*0.15
*0.10
*0.05
0
error obtained with the one-thermistor bridge. Figure 17 shows
to ambient temperature variations as a function of time in the
bridge over a relatively long period of time. Assuming that a
of 5 minutes is necessary to obtain a power reading, Figure 17
-0.05
-0.10
-0.15
1
1
AO
10
24
30 40 50 60 70
TIME -MINUTES
80
90
100
110
Figure 17. Ambient Temperature Variations of Prototype Bridge.
-36-
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Progreqs Report No. 4, Project No. A-271
.........---.....mo.m.????????????mwA.wit? ? ??????
indicates that a maximum error of approximately 0.1 my is possible. However,
data from actual power measurements indicated that power levels as low as 0.5
low could be consistently measured with an accuracy of ! 5 percent. The greater
accuracy of the experimental readings was due to the improbability of the read-
ing being taken at times when the temperature variations were maximum and to the
fact that the time necessary to make the measurement was less tha 5 minutes.
? It ts not possible, at the present time, to measure r-f power at. .a 0.2-mw
level with the desired accuracy because the error due to ambient temperature
varfatiens is equivalent to a relatively large percentage of the r-f power being
measured. Better matching of the two thermistors would reduce the deflections
due to temperature variations and would permit lower values Of r-f power to be
measured with the desired accuracy. Improvement in the bondiug.between ther-
mistor and dissipating body would result ix. a given ambient temperature de-
flection representing a smaller percentage of the power being measured and would
also allow lower level r-f power to be measured accurately.
C. Experimental CI Meter
1. Coaxial Crystal Parameter Bridga
Progress Report No. 3 presented the
made oa the Coaxial Crystal Parameter Bridge.
the bridge in its present form was capable of
of less than 15 percent in magnitude and less
results of passive measurements
These results indicated that
matching impedances with errors
than 5 degrees in phase angle at
drive levels as low as 0.5 my. Considerably greater accuracy (5 percent and 2
degrees) was obtained by increasing the drive level or can be realized by in-
creasing the sensitivity of the coupler elements. However, nu effczt was made
to increase the sensitivity since the_ accuracy presently obtained is adequate
to determine the usefulness of the bridge arrangement.
,ma .?????
-37-
a_
So
Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 ? CIA-RDP81-01043R002300080001-3
.J.namar4
Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
7416
.? .21 4,?????,..???? ? ft .a..mt
...m....m.??????????????? m??????????
r1,?cgress Report No. 4, Project No. A-271
.Additional checks were made on the bridge by utilizing it in a passive
measurement setup to measure the series resonant frequency and resistance of a
number of crystal units furnished by USASEL. The resulting bridge measurements
were compared with those obtained by USASEL and with those obtained at Georgia
Tech with the 'present crystal measurement standard.
Figure 13 shows a picture of the passive system used. The Marconi 1066/1
Signal Generator which was used as the external signal.source exhibited a short
?
?
OMM1101.1?????
4??????111???.????????
..1???????? /MIND
Progress Report No. 4, Project No. A-M.
???.-.???????????m?*?a?r?"ir?'ef 5?001.ww0,4*
With the other two crystals, No. Fa-57 and Fa-82, the coaxial .bridge measure-
ment differed from both the Measurements Standard and the USASEL results. How-
ever, caution should be exerc',Jd in the resistance comparisons since infor-
mation was not available as to the conditions under which the USASEleresistance
measurements were made and since the coaxial bridge results were obtained by
measuring the VHF Rheostat resistances with a conventional ohm meter without
regard to phase angle considerations.
time stability that was more than adequate to permit proper bridge nulls to be
1 TABLE II
obtained. The thermistor power meter, also shown" in Figure 13, was not used to
1 COAXIAL CRYSTAL PARAMETER BRIDGE MEASUREMENTS
measure crystal drive because of the unavailability'of VHF Rhaostat-Thermistor
1
1
units covering the entire frequency range of the group of crystals. However,
1
. the crystal drive was set at approximately 2 mw for each measurement by meas-
I
urine the voltage across substitution resistors (approximately equal to Ri)
placed in each side mf the coaxial bridge:
Table II compares the results of the bridge measurements with those ob-
tamed at USASEL and with those obtained with the Georgia Tech Crystal Measure-
1
.
ments Standard. In each case a frequency difference of less than 0.001 percent, i
.
(target accuracy) was obtained between the bridge measurement and either of the
two methods used for comparison. The average deviation appears to be approxi-
mately 0.0003 percent from the Measurements Standard and 0.0004 percent from
.
the USASEL measurements.
Although resistance deviations greater than the desired accuracy of t 5
ohms or 10 percent were obtained in four cases, these differences did not exceed
15 percent. With two of these crystals, No. Fa-40 and Fa-44, the differences
occurred only between the coaxial bridge and the Measurements Standard results.
-38-
???? ?
? ?
?
???.????
.. ?
Crystal No.
Coaxial Bridge
Frequency
R
1
Til;i7
52
33
36
30
31
34
44
38
31
37
39
61
leo
110
60
- FI 57
Fa-59
Fa-89
Fa-9l
Fa-103-
FF::::3
Fa-104
Fa-105
Fa-116
Fe-117
Fa-118
'FA-82
Fa-83
Fa-40
Fa-44
(mc/sec)
111.4454144E8
155.02535
154.98305
165.00956
164.96445
164.94949
175.02918
174.89883
174.89625
188.94369
188.9966
195.97879
196.01245
Measurements Stand. USASEL
At
(percent)
+ .00020
+ .00007
.00029
- .00003
'+ .00030
4..00?58
.00065
4 .00046
-, .00037
4 .00010
4 .00041
+ .00055
: :2141
4
.00046
6111
TarTas7
+ 6
+ 1
+ 2
+ 1
+ 3
o
- 1
o
o
- 1
+ 3
4 8
+ 9
413
p 9
e
Atial
Ta-Jiiy
+ 8
+ 5
+ 2
+ 2
+ 4
4 2
- 2
- 1
+ 2
- 4
o.
4 9
4 2
- 4
+ 3
(percent)
- .00068
- .0004o
+ .00023
- .0o068
- .00055
4 .00042
4 .00021
4 .00014
+ .00035
: ::::41:
4 .00049
4 .00002
- .00017
4 .0007o
^
-39-
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Declassified in Part - Sanitized Copy Approved for Release
-11
;7-
50-Yr 2013/10/31: CIA-RDP81-01043R002300080001-3
ommir.
? ? ? 11???? 0.0 am.. woo ....nil. ??????
,a01.1.0immrdW.* lima??????ft? ????/......m./.0???????????m?eame???????????...
??????????11,...1,""V. ???????????????????????4 .??????1441??????? ??? ? g????????? ??????????????????
?????? .?.1???r?????????16. yr t":.?
4.???
Progreaa Report No. 4, Project No. A-271
To further check the unefulnenu of the bridge arrangement the consistency
of the bridge was determined by repeating the measurements. Table III shows
the renults of two mersurement runt, the second of which vas performed one week
after the firet. An may be seen, the frequency differences were considerably
less than 0.001 percent with only 5 of the 15 measurements exceeding 0.0005
percent. In addition all of the renistance values were well below the 5-ohm
or 10-percent desired accuracy.
TABLE III
CHECK OF 2RIEGE REPEATABILITY
;
1
TDEaT
Crystal No.
Frequency
R1
6,f
[If
(mc/sec)
Tar-1;U
(cycles)
(percent)
Fa-57
144.99763
52
+ CIO
+ .00061
0
Fa-59
144-99511
33
+ 130G
.00065
+1
Fa-89
154.97008
36
+ 100
+ .c0006
-1
Fa-91
155.02535
30
530
-.o0034
3
Fa-92
154.98305
31
410
-.00027
2
Fa-103
165.009!.6
34
350
-.00021
2
Fa-104
164.96445
44
60
- .00003
0
Fa-105
164.94949
38
70
- .00004
2
Fa-116
175.02918
34
280
+ .00016
4
Fa-117
174.89993
37
740
- .00042
+14
Fa-118
174.8,1625
39
920
+ x003
+2
Fa-82
188.94369
61
260
- .00014
+3
Fa-83-
188.99636
100
1000
- .00053
-2
Fa-40
195.97879
110
620
+ .00032
-5
Fa-44
196.01245
Eo
+ 1890
+ .00097
1- 1
-40-
- ? -
Progrens Report No. 44 Project No. A-271
It was pointed cut in Progress Report No. 3 that the wevjor portion of tt.4
coaxiAl bride error was due to the inherent unbalance of the basic bridge as-
aembly. To furthel? check this property the crystals were measured in both aides
of the bridge ant, the results compared. These results are shown in Table IV.
Although the rrequency and resistance differences were small the bridAe dinaym-
metry was verified by the conuintent negative frequency and positive resistance
errors.
TABLE IV
CHECK OF MIDGE SYMETRY
Crystra No.
Frequency
R1
17-11-1-sTek
cr1-277-7.2
(mc/sec)
(cycles)
(percent)
Fa-57
144.99760
52
620
.00043
+9
FA-59
144.99511
33
250
.00017
+5
Fa-89
154.97008
36
450
.00029
+3
Fa-91
155.02535
30
- 270
.00017
+2
Fa-92 -
154.98305
31
220
.00014
+.2
Fa-103
165.00956
34
600
.00036
+
Fa-104
164.96445
44
4E0
.00028
+14
Fa-105
164.94949
38
400
.00624
+6
Fa-116
175:02918
34
750
.00043
+7
Fa-117
174.89883
37
-1120
.00065
-4
Fa-118
174.89625
39
- 750
.00043
+3
FA-82
188.94369
61
6o
.00003
-1
Fa-83
188.99636
100
40
.00002
*10
Fa-40
195.97879
110
-1390
.00071
+10
Fa 44
196.01245
Eso
-3040
.00175
_
-141-
-- ?
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/16/31 : CIA-RDP81-01043R002300080001-3
?
ort?
.11?????????
Nr????1114.4.4,..?ao?.10.01...
?IM.?????????=???????.
,?????,?????????
Ammm.10,
Progress Report No. 11.2_ Projpct No.
The crystals were also measured in the coaxial bridge at their overtone
frequencies in the 200- to 300-me/sec frequency range. Since no USASEL measure-
ments were available in this frequency .range, the results were compared only
with those obtained with the Crystal Measurements Standard. The freqaeucy dif-
ferences obtained were well below 0.001 percent in all but two questionable
cases. However, considerable disagreement in resistance measurements was obtain-
ed, especial&y above 250 mc/sec. As of this report date an inveotigation of the
possible causes of these discrepancies had not been made but additional meas-
urements of crystal parameters and VHF Rheostat impedances are planned. A study
of the bridge reaction to possible high frequency crystal equivalent circuits
will also be made in an effort to determine the basic reasons for the resist-
ance differences.
The results obtained with the coaxial bridge over the 100 to 200 me/sec
frequency range indicate that the -p..eaently obtainable accuracy is comparable
with that of other available methods. In the 200- to 500-mc/sec range some
0
question still remains as to the accuracy, particularly in respect to the crys-
tal resistance measurements. Although additional efforts will be made to de-
termine the causes of these resistance measurement discrepancies, the general
accuracy and overall suitability are such that the bridge appears satisfactory
for use in connection with the oscillator circuitry under development.
2. Exzerimental Oscillators
When the Crystal Parameter Bridge technique is used with an active
oscillator, the frequency control is maintained by the crystal impedance varia-
tions near resonance as modified by the bridge configuration. In effect the
crystal characteristic as presented to the oscillator is degraded by the shunt
????
A
1
1
??????????
far,
. - . .
arm of the bridge. In particular, a MAXiMUM impedance change of two to one is
imposed, near bridge balance, by the variable rheostat of the shunt arm.
This impedance degradation, as discussed in Progress Report No. 3 ia the
major factor which prevented satisfactory operation of the Plate Degenerative
Oscillator when used with the Coaxial Crystal Parameter Bridge. Additional ex-
perimental tests were made on this oscillator by utilizing passive elements in
place of the crystal and bridge. These tests have confirmed the suspected ina-
bility of the Plate Degenerative Oscillator to oscillate satisfactorily with a
maximum impedance change of only two to one. This was found to be true reaard-
?????,.....???????????????????????=1????
Progreso Report No. 4, Project No. A-271
less of the phase angle considerations.
The bridge degrading property therefore necessitated an investigation of
additional oscillatory circuitry which would not only meet the original require-
ments set forth in Progress Report No. 1 but would in addition be more sensitive
to the phase and impedance changes exhibited by the bridge-crystal combination.
Of the possible configurations only those which permitted one terminal of the
crystal unit to be grounded and which permitted simple capacitive neutraliza-
tion of Co were considered.
One configuration which appeared to meet these requirements was the capaci-
tance bridge oscillator described in Progress Report No. 2. Two additional ex-
perimental models of this oscillator were constructed during the present report
period. The construction of the first model which is shown schematically in
Figure 18 was similar to that of the original in that it utilized a 2-in, hair.-
pin loop for the primary and a 1-in, loop for the secondary. These loops, how-
ever, were made physically wider in order to aid in reducing the cross coupling
???
- .
-143.
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Declassified in Part - Sanitized Copy Approved for Release
--Inwtmurg
50-Yr 2013/10/31: CIA-RDP81-01043R002300080001-3
411.11111???? .1.,???????afmr.m..?
????????.? 11.1???...??? ? ??? ? ? ? ..?????????.?.... ????????????
tadrena Report No. 4 Project No. A-271
?
4????100.1=0/1m.......?
effects that were observed in the first model. A raraday ahield between the
two loops was also utilized to prevent capacitive cross coupling. A Western
Electric 417A tube which has a rated transconductance of 25,000 mdcromhos was
used in the grounded grid amplifier. Crystal controlled oscillations could be
obtatned throughout the 200- to 500-mc/sec frequency range of the tuned circuit
provided the Co of each crystal used was individually neutralized.
C4
1000
jfd
ERIE NPO
CI 1.5 - 7?1.Lfel
C2
50).q.sid
R2
470
Cv
1- 12??fd
Figure 18. Capacitance Bridge Oscillator.
In order to determine qualitatively the sensitivity of the oscillator to
the resonant characteristics of a bridge-crystal combination, a shunt resistance
of 50 Ohms was placed across the crystal. This resistor in effect simulated
the degrading property that wou.d be exhibited by the Coaxial Crystal Parameter
.0111F
. "." ?? ? ?
1
01.101????
Prosrenn Report No. 4, Project No, A-271
Bridge. Under this condition crystal controlled oacillationn could still be
obtained throughout the 200- to 500-mc/sec frequency range.
In Jta present form two practical considerations prevent a further analysis
of this circuit when used with the Coaxial Crystal Parameter Bridge. The _first
is the tuning capacitor CI whose turn of adjustment for the entire 200- to
300-me/sec range makes tuning very difficult. The second is the physical ar-
rangement which is such that the coaxial bridge cannot be conviently connected
in the circuit. It is contemplated that additional models will be constructed
which will eliminate these two difficulties and permit a more complete analysis
of the circuit to be made.
A second experimental model of this same basic configuration vas construct-
ed which utilized a modified Mallory UHF inductuner (shorted line) tunable from
appioximately 550- to 40-mc/sec. The modification consisted of placing two
mirror image lines back to bank in a manner such that mutual coupling could be
obtained and such that both lines could be adjusted simultaneously. A concer
foil Faraday shield was inserted between the lines and the oscillator compon-
ents were mounted directly on the inductuner frame. The sclumatie diagram is
essentially that of Figure 18 except a type 6AN4 tube was utilized and the tun-
ing capacitor C1 was eliminated. Crystal controlled-oscillations were obtained _
at frequencies as high as 420 mc/sec with this oscillator. Co neutralization
could be accomplished in most ceces although the capacity required was con-
siderably less than expected. Several crystals were tried with this oscil-
lator and satisfactory operation was obtained in the majority of the cases. In
particular the crystals of Table V were oscillates, at -the Trequencies and over-
tones indicated. Complete Co cancellation could not be obtained with Crystal
J1.
Declassified in in Part - Sanitized C .y A
ease
0
5 - r 3/10/31 : CIA-RDPF31-ninaqpnnormrlorw-w-,,
Declassified in Part - Sanitized Copy Approved for Release
50-Yr 2013/10/31: CIA-RDP81-01043R002300080001-3
- .-114.11V
?
'
Progress Report No. 4 Project No. A-271
effects that were observed in the first model. A Fsraday shield between the
two loops was also utilized to prevent capacitive cross coupling. A Western
Electric 417A tube which has a rated transconductance of 25,000 xdcromhos was
used in the grounded grid anplifier. Crystal controlled oscillations could be
obtaLned throughout the 200- to 300-mc/sec frequency range of the tuned circuit
provided the Co of each crystal used was individually neutralized.
RI
15K
ERIE NPO
Cl 1.5 - 7?1.tfd
Figure 18. Capacitance Bridge Oscillator.
In order to determine qualitatively the sensitivity of the oscillator to
the resonant characteristics of a bridge-crystal combination, a shunt resistance
of 50 Ohms was placed across the crystal. This resistor in effect simulated
the degrading property that wou-d be exhibited by the Coaxial Crystal Parameter
111???????
?
IM.V.0911.5.yrr.".
Progrens Report No. 4, Project No. A-271
Bridge. Under this condition crystal controlled oscillat.tons could still be
obtained throughout the 200- to 300-mc/sec frequency range.
In its present form two practical considerations prevent a further analysis
of this circuit when used with the Coaxial Crystal Parameter Bridge. The first
is the tuning capacitor C1 whose turn of adjustment for the entire 200- to
500-me/sec range makes tuning very difficult. The second is the physical ar-
rangement which is such that the coaxial bridge cannot be conviently connected
in the circuit. It is contemplated that additional models will be constructed
which will eliminate these two difficulties and permit a more complete analysis
of the circuit to be made.
A second experimental
model of this same basic configuration was construct-
?
ed which utilized a modified Mallory UHF inductuner (shorted line) tunable from
appioximately MO- to 1450-mc/sec.D The modification consisted of placing two
mirror image lines back to bank in a manner such that mutual coupling could be
obtained and such that both lines could be adjusted simultaneously. A eonper
foil Faraday shield was inserted between the lines and the oscillator compon-
ents were mounted directly on the inductuner frame. The schosaticodiagram is
essentially that of Figure 18 except a type 6AN4 tube was utilized andethe tun-
ing capacitor C1 was eliminated. Crystal controlled-oscillations were obtained_
at frequencies as high as 420 mc/set with this oscillator. Co neutralization
could be accomplished in most caces although the capacity required was con-
siderably less than expected. Several crystals were tried with this oscil-
lator and satisfactory operation was obtained in the majority of the cases. In
particular the crystals of Table V were oscillatea at the 'frequencies and over-
tones indicated. Complete Co cancellation could not be obtained with Crystal
-
???
Declassified in in Part - Sanitized C .y A
df
ease
0
5 - r 3/10/31 : CIA-RDPF31-n1n4qpnnormrlonrw-,,
Declassified in Part - Sanitized Copy Approved for Release
- w
50-Yr 2013/10/31: CIA-RDP81-01043R002300080001-3
? ? .4, cp. ?????????......
.???????
???????.?m.... ?
...-???????.** adm.?? ???????... ?????????????
Pro7ess Report No. 4, Project No. A-271
No. 1-3 at 353 me/sec but lock-in oscillations were obtained. Co cancellation
was complete, however, from slightly above 555 mc/sec to well beyond the next
overtone oscillation of this particular crystel which occt.rred at 400 me/sec.
Although very little is known at the present time regarding the frequency c A-
trolling properties cf crystals at these overtones, it is of interest to note
the position of these particular crystal responses on the Smith charts presented
In the appendix. The proximity of these responses to the higher conductance
portion of real axis appears to be significant and indicates the need of further
investigation.
TABI.E Y
CRYSTALS OPERATED IN CAPACITIVE BRIIGE OSCILLATOR
Crystal No.
Fundamental
FrequencyTic
Oscillating
Fre uenci
Overtone
15
13
(me see)
353
564
1-3
Fa-44
sec
23.5
28
3-W
25
375
15
Fa-59
Fa-118
29
35
376
382
0
13
11
Fa-91
31
4o3
15
1-3
23.5
. 400
17
Fa-44
28
42o
15
-6-
? ????????????????? ???????? ...???????
?
.4
;
???????immmaeoMMII.V1=1.????11110.111?11.
ELTAress Repo:t No. 4, Project No. A-271
VI. CONCLUSIONS
Calibration data and actual crystal measurement data Indicate that the
best accuracy presently obtainable with the Crystal Measurements Standard is
about 5 perceni. fr impedance magnitude and t 4 degrees for phase angle. This
is obtained by using a General Radio Type 1602-B Admittance Meter with a half-
wavelength transmission Une between the meter and the crystal. This accuracy
it possible only under ideal conditicns and only for certain crystals. The
accuracy is limited principally by the accuracy of the Admittance Meter. Be-
cause of the poor condition of the available Admittance Meter, a new instrument
_would probably give a considerable improvement in .accuracy.
Investigations concerning the presently used crystal equivalent electrical
circuit indicated that the circuit does not satisfactorily represent all crystals
at high frequencies. In particular, the need for a capacitance, Col, directly
across the pin of the crystal holder is indicated. This study did not progress
sufficiently to assert definite conclusions concerning the other elements of
the equivalent circuit.
Numerous measurements on adtual high frequency crystals resulted in close
frequency agreement between the Crystal Measurements Standard, the Coaxial
Crystal Parameter Bridge and other measurement methods. Measurements of equiva-
lent resonant resistance did not provide the agreement anticipated. Disagree-
?
merits in both frequency and resistance can possibly be accounted for by the
lack of standardization of the method of cancellirr, Co with different measure-
ment systems. Such standardization is practical only by first .rriving at a
satisfactory equivalent circuit.
.????
-47-
_r
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Declassified in Part - Sanitized Copy Approved for Release
IL,
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LI 4,
A
?
A
01?Nomarod?
le.. ? ? ? ? ? ?? ? ?????? ? ? IA
???????=??????=?fiA???? ?.? ???????????????????? ?????????????????IMMAI. ?????????????? *MO ..???????????????. ...M. ???00????????m???????/1.???????????? ??????
? ???????????????????? ?????????? 111. UN/ ?
.? ...? , ? ????? '" ? ? ?? ? ????????.... . ?
? e.P? ..4.04.*Artr, ? I
Etagrens Report .No. h, Project No. A-271
A comparison with other power measurements indicated the prototype ther-
mlotor-bridge power meter to br. capable of menauring r-f power in the range
from 0.5 mw to 4.o mw with an accuracy of t 5 percent. Better matching of the
two thermistors and improvement in the bonding between the thermistor and dissi-
pating boey nhould permit lower values of r-f power to be measured with the de-
sired accuracy.
An experimental capacitance bridge oscillator was constructed that demon-
otrated an ability to maintain crystal controlled oscillations under conditions
similar to those imposed by the Coaxial Crystal Parameter Bridge. A enfitf4ee
physical arrangement which will accept the coaxial bridge will be required in
order to fully determine the capabilities of this configuration. Crystal con-
trolled oscillations were obtained with a similar configuration at frequencies
as high as 420 mc/sec. The present inadequate knowledge of the frequency con-
trolling properties of crystals at these overtones reveals the need for further
investigation of the results obtained.
??
-48-
Prrens Nojj, Projcct No. A-2'
VII. PROGRAM FOR NEXT QUARTER
Work during the next quarter will be a continuation of that reported in
the preceding pages with emphasis on the following objectives!
1. perform additional tents of the prototype cryatal power measuring sys-
tem to determine its accuracy,
2. continue the inveotigation of oscillator circuits for use with the
Coaxial Crystal Parameter Bridge;
3. procure and evaluate new OR admittance meters and HP UHF bridges for
use in the Crystal Measurements Standard; and
4.
investigate additional commercial equipment for use in the Crystal
Measurements Standard.
4
Approved by:
W. B. Wrigley, Rea
Communications Branch
of the
Physical Sciences Division
- ?
-49-
Submitted by:
41474Al
lear.;:;\
Douglas, W. Robertson
Project Director
Declassified in Part- Sanitized Copy Approved for Release ? 50 -Yr 2013
. - 1-01
Declassified in Part - Sanitized Copy Approved for Release
_,...rwwzrAvi;*
50-Yr 2013/10/31: CIA-RDP81-01043R002300080001-3
'MIAMI' ? 'IC.
f???????? ?????? ?
Progress Report No. 4, Project No. A-271
VIII. PERSONNEL
BiographiPal sketches of the key technical personnel were included in
Progress Reports No. 1 and 2. The time contributed by each during the present
period is:
Douglas W. Robertson Project Director
Samuel N. Witt, Jr. Research Engineer
William R. Free Aest. Research Engineer
James E. Lane ? Technical A.,sistant
4007084000
-50-
? ...ft. ?
????
Full Time
2/3 Time
Full Time
1/2 Time
tons
Ce-we.?+?-? ,P9~,
;
4
4
dl?ImIMM
Progress Report No. b, Project No. A-271.
DC. APPENDIX
A. Addendum
Figure 15, page 33 of Progress Report No. 3, has been found to be in er-
ror. The scale on the R1/R2 Ratio (abscissa) was inadvertently shifted two
grid divisions. The first grid line should be labeled 0.5 rather than 0) the
third line should be 1.0 instead of 0.5) 1.0 should be 1.5, etc. With the
corrected scale, the K factor obtained for an RI/R2 ratio or 1 is .675
(actual point) which corresponds very closely with the power ratios of Tables
I and II (first bonding condition) of that report.
B. Admittance Characteristics of Measured Crystals
This section contains 15 figures. Refer to page v,.LIST OF APPENDIX
FIGURES, for a listing of the crystals that were measured.
?????????..n.
-51-
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?
Declassified in Part - Sanitized Copy Approved for Release
50-Yr 2013/10/31: CIA-RDP81-01043R002300080001-3
??????
Progress Report No. 4, Project No. A-271
meas.+.
mor/....???*?,???!????????????1??????
?
????=??????=0??????????.......... Ey.
no???????????????"...r..,?... ?
Figure A-1. Admittance Characteristics of Cryatal Vo. Fa-57.
-52-
???? 1
????????
?
Progress Report No. 4, Project No. A-271
Figure A-2. Admittance Charqcteristics of Crystal No. Fa-59.
?????????ar.
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-53-
Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
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Pr-Tress Report No. 4, Project No. A-271
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Figure A-3. Admittance Characteristics of Crystal No. Fa-89.
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Figure A-4. Admittance naracteristics of crystal No. Fa-91.
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
Declassified in Part - Sanitized Copy Approved for Release . 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
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Figure A-5. Admittance Charact.eristics of Crystal No. Fu-92.
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Progress Report No. 4, Project No. A-271
Figure A-6. Admittance Characteristics of Crystal ho. Fa-103.
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
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Progress Report No. 4, Project No. A-271
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Figure A-7. Admittance Characteristics of Crystal No. Fa-104.
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Progress Report No. 4, Project No. A-271
Figure A-8. Admittance Characteristics of Crystal No. Fa-105.
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
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Figure A-9. Admittance Characteristics of Crystal No. Fa-116.
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Figure A-10. Admittance Characteristics of CrystP1 No. la-117.
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
Declassified in Part - Sanitized Copy Approved for Release 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
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Figure A-14. Admft?ce -:-...zr-icteriztler of Crysta. No. Fa-40.
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
Declassified in Part - Sanitized Copy Approved for Release 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
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Figure A-15. Admittance Characteristics cf Crystal No. Fa-44.
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
Declassified in Part - Sanitized Copy Approved for Release @ 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
Declassified in Part - Sanitized Copy Approved for Release @ 50-Yr 2013/10/31 : CIA-RDP81-01043R002300080001-3
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