FIRST BIMONTHLY REPORT OF THE MINIATURE IF AMPLIFIER PROGRAM

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03424A000500050025-6
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 11
• Document Creation Date: December 22, 2016
• Document Release Date: February 15, 2012
• Sequence Number: 25
• Publication Date: July 1, 1959
• Content Type: REPORT

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CONFIDENTIAL
First Bimonthly Report
Of The
Miniature IF Amplifier Program
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Prepared by:
1-July-1959 to 1-Sept.-1959
ORIGINAL CL ry
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TABLE CF CONTENTS
Page No.
1. Purpose . . . . . . . . . . . . . . . . . . . . . 1
II. Abstract . . . . . . . . . . . . . . . . . . . . . 2
III. Factual. Data. . . . . . . . . . . . . . . . .. . 2
(a) Crystal Filter Program. . . . . . . . . 2
(b) Ceramic Resonator Program . . . . . . . . . 4
IV. Conclusions . . . . . . . . . . . . . . . . . . . 7
V. Future Plans o . . . . . . . . . . . . . . . . . . 7
VI. Identification of Key Technical Personnel . . . . 8
?ITIAL
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I. Purpose
As described in the "Proposal For The Construction Of Miniaturized IF
Amplifier Packages," dated 9-March-191&9, the purpose of this program is to
bring to fruitition work previously carried out in the development of IF ampli-
fiers using novel techniques and devices.
Two miniaturized IF amplifier packages will be constructed. One will
be suitable for a single conversion superheterodyne receiver and will employ
a miniaturized crystal filter as the bandpass determining element. This
filter will be built using the techniques developed as a result of work per-
formed under the continuation of the Radio Circuit Study program
but employing crystals fabricated specifically for this applica-
tion rather than standard units.
The second packaged amplifier will consist of a high and low IF am-
plifier combination with mixer and crystal controlled local oscillator stages,
suitable for use in a double conversion receiver. In the low IF amplifier,
bandwidth determination and interstage coupling will be by means of ceramic
resonators rather than conventional inductors and capacitors. Techniques for
using these ceramic components were developed during the original Radio Cir-
cuit Study but were subsequently discontinued because at
that time no material was available which was sufficiently temperature stable.
The materials problem has now been largely solved and ceramic transformers
meeting center frequency stability requirements over the temperature range
from -1&0? to ;!&0?C can be fabricated.
At the conclusion of this program two miniaturized IF amplifier
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packages will be delivered. They may then be evaluated and compared with re-
spect to temperature stability, physical size, battery drain, etc.
II. Abstract
This report, covering the first two-month period describes the pre-
liminary work which has been performed in the two amplifier programs. The
amplifier for the single conversion receiver employs a crystal filter.
Initial efforts have been concerned with the design and construction of this
filter which, while very small (one cubic inch will be the largest single
component in the amplifier and will consequently have a profound effect on
the packaging of the remainder of the components.
For the second amplifier, preliminary work has been concerned with
the preparation of suitable ceramic from which to fabricate the lumped filter
and the interetage coupling transformers. From the materials prepared, trans-
formers have been built and measurements of their electrical performance made.
Some circuit work has been carried out in order to evaluate the transformers
under conditions which are similar to those existing in the final amplifier.
III. Factual Data
(a) Crystal Filter Program
During previous programs the problems of realizing a miniaturized
filter suitable for use in a single conversion 3-30 MC receiver have been
studied. In the interests of image rejection, a high IF frequency is desirable
whereas for narrow pasabands a low IF frequency is more suitable. A filter
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with suitable bandpass characteristics operating at a relatively high IF fre-
quency can be designed making use of the properties of crystals. However,
commercially available crystal filters are quite large, making their use in
highly miniaturized equipment very difficult.
Some work was done on the development of a miniaturized crystal
filter under a previous program. The resultant filter was substantially
smaller than anything then commercially available. It utilized, however,
commercially available crystals.
The development of the present miniaturized crystal filter is being
carried out with the benefit of the experience and equipment of
This group,
located inl lis in a position to grind and mount crystals
specifically for the present application.
During the present reporting period a technique has been developed
for mounting crystals operating in the 2 MC range in standard type HC-18/U
holders. The intermediate frequency to be used in the present amplifier is
2.281 MC. Various methods of grinding quartz crystal blanks have been in-
vestigated in order to arrive at a satisfactory procedure for reducing
spurious response. With the edges of both sides of the crystal beveled,
spurious response of the individual crystals is reduced to -L0 db or better
at a spacing of approximately 250 kc from the crystal frequency.
The electrical circuit will take the form of a two-section, half-
lattice filter. Exclusive of crystals, the transformers at both input and
output of the filter will be the most critical elements. Transformer core
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materials supplied by a number of manufacturers have been evaluated. A
material will be selected to satisfy the requirements of Q, inductance and
temperature stability while conforming to physical size specifications.
(b) Ceramic Resonator Program
A program of materials evaluation and development has been conducted
in the las a joint effort of the
One of the experimental materials recently fabricated and evaluated has a
temperature stability that makes it suitable for use over the temperature
range from -65? to +160?C. A curve of the frequency constant (resonant fre-
quency normalized to a one inch sample) variation with temperature of this
material is shown in Figure 1. Over the whole temperature range there is
less than a .3?/6 change in the frequency constant. For the range of interest
to this program, there is less than a .2?/6 change of frequency (-40?C to
+b0?C. )
Several ceramic transformers for use as interstage coupling elements
in the transistor amplifier were fabricated from this material. However, when
these transformers were tried in the transistor amplifier breadboard circuit,
the bandwidth of a single stage was found to be too narrow.
The bandwidth of such a single stage circuit is a function of several
factors. The bandwidth of a ceramic transformer interstage coupler depends on
both the ceramic material properties and the terminating impedances used with
it. In this case the terminating impedances are the output impedance of the
preceding transistor and the input impedance of the succeeding transistor.
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is
0
FREQUENCY CONSTANT VERSUS TEMPERATURE
FIGURE I
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The ceramic material properties of importance are the electro-
mechanical coupling coefficient and the mechanical Q. A low coupling co-
efficient will increase the insertion loss of the ceramic element and decrease
the bandwidth, while a high mechanical Q will decrease the insertion loss and
decrease the bandwidth. The coupling coefficient of this experimental
material is considerably in excess of that required for this application.
The trouble lies with the mechanical Q. With the terminating impedances,
which are largely capacitive, supplied by the transistors used in this ampli-
fier, the bandwidth is primarily a function of the mechanical Q of the ceramic
transformer material and will increase as the mechanical Q is decreased. This
experimental material is therefore unsuitable for this application as it
stands, unless a new transistor or a new operating point for the transistors
can be found such that the capacitances of the transistor input and output
can be decreased.
The personnel of the feel
that it is possible to fabricate a new material with essentially the same
temperature stability and a lower mechanical Q. Such a modified material
will be attempted and available for evaluation in the near future. Meanwhile
some ceramic transformers are being fabricated from other ceramic materials
with less but possibly sufficient temperature stability and lower mechanical Q.
As stated earlier the bandpass characteristics of a ceramic trans-
former are to a significant extent a function of the terminating impedances
on either side of the transformer. For this reason it is important, in
evaluating the transformers, to do so in a circuit configuration which is
similar to that in which they will ultimately be used. Consequently several
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stages of the 455 kc amplifier were constructed in breadboard form to serve
as a transformer test jig.
The narrow'bandwidth exhibited by the transformers which have been
tested so far was initially attributed to an excessive input capacitance to
the subsequent transistor. A capacitive divider was consequently used at the
transformer output to reduce the effective load capacitance. The improvement
in bandwidth was quite marginal. Further tests showed that, even when termi-
nated in a pure resistance, the transformer bandwidth was insufficient.
In the interests of minimum size for the amplifier it was planned to
use Raytheon CK17 subminiature transistors and initial circuit work has been
carried out with this type of transistor. However, when additional units were
ordered it was learned that production of these transistors has been suspended.
At the time of writing it is not clear when they will become available again.
During the previous program which resulted in the construction of
the miniaturized 3-30 MC receiver, an effort was made to use a 2.736 MC crys-
tal packaged in a miniaturized case. It was found however that while room
temperature operation was satisfactory, over the temperature range from -110?
to +lt0?C the performance deteriorated. Further work in the crystal packaging
field has resulted in what appears to be a satisfactory method of mounting a
crystal of as low a frequency as 2.736 MC in a miniature case. If tests show
that operation is as satisfactory as it appears, at present, to be, an appre-
ciable volume will have been saved in the design of the local oscillator
which will be incorporated in the ceramic transformer IF amplifier package.
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IV. Conclusions
The crystal filter work is progressing satisfactorily. Methods have
been established for keeping down spurious responses. Other than the crystals
themselves, one of the more difficult portions of the filter development is
the selection of a suitable core material for the filter input and output trans-
formers. Evaluation of core materials is continuing.
Measurements made of initial batches of ceramic for the interstage
coupling transformers to be used in the second IF amplifier package have shown
that temperature stability is more than adequate for the present application.
However the bandwidth obtainable is not sufficient. This is due to too high
a mechanical Q in the material. A second batch of material is being prepared
in which it is anticipated that this problem will be solved.
Future Plans
No work is scheduled on the crystal filter amplifier itself until
after completion of the filter. According to the original plans the filter
will be completed by 31-Dec.-1959. At the present time there is no reason to
revise this schedule.
The ceramic transformer development is scheduled to be completed by
1-Nov.-1959. Until that time, circuit work will be confined to that necessary
to evaluate the transformers and lumped filter as they are fabricated. Despite
the bandwidth problem mentioned elsewhere in this report it is not anticipated
that any revision of the filter and transformer completion date will be re-
quired.
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