FINAL AND TENTH BIMONTHLY REPORT ON THE AUTOMATIC TRANSMITTER PROGRAM

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03424A000800010048-2
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 38
• Document Creation Date: December 22, 2016
• Document Release Date: February 8, 2012
• Sequence Number: 48
• Publication Date: March 8, 1960
• Content Type: REPORT

.1 _
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
CONFIDENTIAL
Final and Tenth Bimonthly Report on
,
the Automatic Transmitter Program
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REASON
Period:
DOC REV DATE AU:BI? BY
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DRIB CLASS J61___ PAW ,31n__ BO GLASS
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8-March to 31-May-1960
. _
Prepared by:
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Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
Table of Contents
I Purpose 1
II Abstract 1
III Factual Data 2
1. The Transmitter 2
I Introduction 2
ii Automatic Tuning 3
iii Final Arrangement of Transmitter Circuitry . . ? 6
iv Auxiliary Circuitry 7
v The Keying Circuit 9
2. The Automatic Impedance Matching Unit 10
i Introduction 10
ii Considered Approaches 10
iii Final Version of Impedance Matching Circuitry. ? 13
3. The Power Supply 16
Introduction 16
ii Specific Circuitry 16
iii Time Delay Circuit 17
4. Auxiliary Power Supply 18
Introduction 18
ii Specific Circuitry 18
IV Conclusions 19
V Future Plans 23
VI Identification of Key Technical Personnel 25
Appendix 26
Operating Instructions 26
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
Purpose
In the First Bimonthly Report the purpose of this program was stated.
At that time, since the program constituted an effort to advance the state of
the art,a considerable portion of that which was written was, necessarily, of
a speculative nature. It is worthwhile, at the conclusion of the program, to
compare the actual course of the program with the projected program as outlined
in the First Bimonthly Report.
The first and second paragraphs of the original "Purpose" remain
perfectly valid. The third paragraph refers to the two approaches, solid
state and mechanical, which were to be taken in order to realize the automatic
tuning and impedance matching functions. Both approaches were studied and
the resultant transmitter incorporates a combination of the two methods, a
mechanical servo system being used for the impedance matching function for
reasons discussed in the body of this report. Advances in the transistor art,
which it was hoped would result in the availability of an RF output power of
10 watts over the 3-30 mc range, did not take place sufficiently rapidly for
inclusion in the present transmitter. Semiconductor device development did
not, however, form part of the present program.
II Abstract
This report, in addition to describing the complete transmitter, gives
an outline of the design history showing the reasons for the various decisions
which were made in arriving at the final version. The material is broken into
two parts, one being concerned with the transmitter itself while the second
covers the automatic impedance matching portion of the equipment. Complete
circuit diagrams are included as well as a set of operating instructions.
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
Declassified in Part- Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
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The equipment delivered at the conclusion of this program consists
of two units, one case containing the transmitter and antenna matching unit
with appropriate built in power supplies to operate from a 12 volt DC source.
The second case houses an auxiliary power supply permitting operation from
a large range of AC line voltages with frequencies of 50 to 60 cycles per
second. A feature of this auxiliary supply is an indicator system which
permits the operator to adjust the unit to the correct line voltage setting
without having to know what the line voltage is.
The program was originally divided into three phases. This report
is the final report marking the conclusion of the second phase. The first
phase was concerned with the electrical design of the equipment to meet
the original specifications to the extent permitted by the state of the art.
The second phase covered the construction of the equipment in deliverable
form but without attempting the ultimate in miniaturization by packing
components with the maximum density. The third phase, for which no negotiations
have yet taken place, would cover packaging the equipment in as small a physical
volume as possible - preferably a package measuring 3" x 6" x 11/2" as opposed
to the present case which measures approximately 411/16" x 91/4" x 21/2".
III Factua1 Data
1 The Transmitter
(i)
Introduction
The specifications call for a transistorized transmitter covering the
3-30 mc frequency spectrum with an output power of 10 watts. The transmitter
should be designed for CW operation either from an internal key or by means
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
Declassified in Part- Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
-3-
of an external automatic keyer. Other than setting a band switch and plugging
in an appropriate crystal, the operator should not be required to make any
tuning adjustments. Below 15 mc operation is on the fundamental crystal
frequency while from 15-30 mc the third overtone mode is used. While under
normal circumstances the tranqmitter will be crystal controlled, provision
is required for the connection of an external VFO.
(ii) Automatic Tuning
As was reported in earlier Bimonthly Reports several approaches
were tried in an attempt to perform the automatic tuning function. Of the
electrically variable tuning devices available, variable capacitors were
felt to be more desirable than variable inductors since with the latter it
is customary to supply a current to the device for as long as the particular
value of inductance is required. This necessitates a constant power drain
and is not compatible with the design objective of high efficiency. With
variable capacitances, it is customary to maintain a voltage across the device
in order to obtain the required value of capacitance. However, the device is
usually of extremely high resistance so that there is virtually no power required.
Two types of electrically variable capacitor appeared to be potentially
useful to this project. One was the "Varicap" type of capacitor consisting,
essentially, of a back biased diode. The second capacitor makes use of a
ceramic dielectric, the dielectric constant of which is a function of the
applied voltage. Some experiments were made on this type of capacitor but at
the present state of materials development it did not offer any advantages
over the back biased diode type and introduced the disadvantage of quite
high bias potentials. This approach was consequently dropped.
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
Considerable effort was put into the "Varicap" approach. This led to
encouraging results but necessitated automatic band switching since it was,
naturally, not possible to cover the required tuning range with one set of
voltage variable capacitor diodes. A successful automatic band switching
circuit was designed which permitted operation in the following manner.
After insertion of the crystal the DC voltage on a "Varicap" type device
was swept from zero to a high value, limited by the maximum permissible
inverse voltage which could be applied to the diode. The capacitance was
consequently changed from a high value to a low value. Since the "Varicap"
was in parallel with a coil, the parallel resonant frequency of the resultant
tank circuit was swept from a low frequency (3 mc) to a high frequency. The
oscillator was designed so that it would not oscillate unless the tank cir-
cuit was tuned to the crystal frequency. If, during the sweeping action,
the resonant frequency of the tank circuit coincided with the crystal fre-
quency, oscillation commenced. A portion of the oscillator output was
rectified and used to stop the sweeping action so that the tank circuit
remained tuned to the appropriate frequency.
If, during the sweeping action, the tank circuit had not passed
through the correct frequency by the time the "VaricapII voltage reached
its maximum value, a threshold was crossed which resulted in the operation
of a switching circuit. This circuit changed the setting of some transistor
RF switches resulting in a smaller portion of the inductance being included
in the tank circuit. The sweeping voltage across the "Varicap" was reduced
to zero and the sweep restarted. This process of sweeping the capacitor
value and changing taps on the coil continued until the correct frequency
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
-5-
was reached. It was consequently possible to cover the required frequency
range, the only decision required of the operator being to set a band-switch
to either the 3-15 mc or the 15-30 mc position. This was necessary since
the specifications call for the use of fundamental crystal control only as
high as 15 mc, the 5-10 mc crystals being used over again as third overtone
units to cover the 15-30 me range. The bandsvitch indicated to the equipment
whether fundamental or third overtone operation was required.
This approach was eventually dropped for two reasons. Although it
was possible to track the tuning of the driver stage with that of the
oscillator, using the same control circuitry, as the power level of the
RF increased from one stage to the next, the effective capacitance change
obtainable from the "Varicaps" became smaller and smaller. This difficulty
arose from the necessity of keeping the diode reverse biased over the whole
cycle despite a large RF swing. As a result of the small tuning range it
would have been necessary to use an unreasonable number of coil taps in order
to operate over the 3-30 mc spectrum. Furthermore, on a different program,
which was being carried out concurrently, very encouraging results were
being obtained with broadbanding techniques.
The transmitter, in its final form is broadbanded throughout, resulting
in a very significant reduction in the number of components with the attendant
advantages of increased reliability and reduced size requirements and power
drain. The broadbanding process has necessitated the use of special high
frequency ferrite torroidal transformers. As may be seen from the circuit
diagram, Figure 1, the whole RF circuitry is of a balanced nature with two
transistors in the oscillator, two buffer transistors, two driver transistors
Declassified in Part - Sanitized Copy Approved for Release 2012/02/98: CIA-RDP78-03424A000800010048-2
Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
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Declassified in Part - Sanitized Copy Approved for Release 2012/02/08: CIA-RDP78-03424A000800010048-2
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