PROPOSAL TO MODIFY SYSTEM 4 TO CORRECT FOR TEMPERATURE EFFECTS AND TO ELIMINATE SPURIOUS SIGNALS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP81B00878R001400010036-2
• Release Decision: RIFPUB
• Original Classification: S
• Document Page Count: 5
• Document Creation Date: December 22, 2016
• Document Release Date: August 19, 1999
• Sequence Number: 36
• Publication Date: August 22, 1958
• Content Type: REPORT

Approved For Release 2009/04/10: CIA-RDP81 B00878R001400010036-2
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COPY / OF f
Proposal to Modify System 4 to
Correct for Temperature Effects and to
Eliminate Spurious Signals
August 22, 1958
CMCC Document No. 1133X5. 69
Copy / of 12 Copies
(This documents contains a total of 5 sheets
including this title sheet)
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1. General
a. During environmental testing performed on System 4
equipment, it has been observed that the sensitivities of the Band
1A and Band 1B receiving channels became appreciably degraded
under conditions of extended periods of operation. at high altitude.
Some corrective measures have been incorporated within the
limitations imposed by test and delivery schedules. However,
Band 1 receiving equipment still suffers from the effects of the
operating environment to a greater extent than the other receivers
in the system. Redesign as described herein is proposed to correct
this difficulty.
b. It is difficult to eliminate completely the spurious
signals originating in the second local oscillators of both Band 1A
and Band 1B receiving channels. If false locks with the accompanying
dead time and waste of film are to be avoided, the lock-on circuits
must be disabled at certain points in the scan cycle. This results
in the loss of some of the potential frequency coverage. Repackaging
of the first i-f assemblies in both Band 1A and Band 1B receiving
channels as described herein is proposed as the most effective and
reliable means for eliminating the spurious signal effects.
2. Proposed Redesign to Correct for Temperature Effects
a. High temperatures are developed in the Band 1 receiving
equipment when operated at high altitude. This causes the following
undesirable changes in the electrical characteristics of several
important circuits of each receiving channele
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The frequency of the second local oscillator drifts.
The center frequency of the first i-f amplifier drifts.
The gain of the first i-f amplifier decreases.
The gain of the second i-f amplifier decreases.
The crossover frequency of the AFC discriminator
drifts.
b. Some corrective measures taken, with partial success,
have included-
(1)
(2)
(3)
Replacing a temperature-sensitive tuning inductor in
each second-local-oscillator circuit with a more
suitable type.
Increasing the first i-f amplifier bandwidth of each
channel, thus reducing the effect of the remaining
second-local-oscillator frequency drift on sensitivity.
Eliminating a buffer-amplifier tube for each second
local oscillator, thus reducing the heat dissipated in
this location.
(4) Incorporating in the equipment an additional fan for
cooling the respective assemblies containing the first
i-f amplifier and second local oscillator. of each channel,
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c. It is proposed to redesign the first i-f and second i-f
assemblies of each of the receiving channels as follows:
(1)
(2)
All frequency-determining components will be chosen
for improved temperature stability. In cases where
the variable inductors now used do not have the required
stability, suitable variable capacitors, such as the
piston type with glass or quartz dielectric,will be used.
The double-tuned transformers used in the second i-f
amplifier will be redesigned for improved temperature
stability.
3. Proposed Redesign to Eliminate Spurious Signals
a. Harmonics of the second-local-oscillator frequency are
picked up in the first mixer and cause the respective receiving
channel to lock at several points in its scan cycle. Various correc-
tive measures have been attempted, such as additional decoupling
and shielding, with some results in spurious-signal reduction.
However, in order to reduce such effects reliably and consistently
below the threshold level, much better shielding is needed for the
circuits associated with the oscillator.
b. In order to present spurious signals originating in each
second local oscillator from interfering with the operation of the
respective receiving channel, it is proposed to repackage each of
the first i-f assemblies. Better shielding will be provided for the
circuits associated with the second local oscillator. Additional
shielding will also be incorporated to prevent oscillator energy from
traveling inside the amplifier from output to input.
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c. Both the second mixer and second local oscillator will
be located in a shielded compartment. Where possible electrically,
connections will be brought into this compartment via feedthrough-
type bypass capacitors. The output stage of the first i-f amplifier
will be located close to the shielded compartment, so that ground
current returning to the oscillator travel the shortest possible
path.
d. All tubes will be mounted inside the first i-f assembly,
since experience with the present amplifier design indicates that
the externally mounted tubes cause conditions highly conducive to
osciallator leakage. It is proposed to. include spring fingers in the
amplifier cover to contact the tube shields, thus dividing the
amplifier into a series of compartments and minimizing waveguide
,coupling of oscillator energy from output to input.
e. Cooling fins on the back of each amplifier will receive
forced air from the additional fan which has already been provided,
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This document contains information affecting the national defense of the United States within the meaning of the Espionage Lows, Title
Approved For Release 2009/04/10: CIA-RDP81 B00878RO01400010036-2 by law.