FIFTH INTERIM REPORT ON THE VLF FERRITE ANTENNA DEVELOPMENT PROGRAM

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03424A000500010016-0
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 28
• Document Creation Date: December 22, 2016
• Document Release Date: April 10, 2012
• Sequence Number: 16
• Publication Date: January 1, 1957
• Content Type: REPORT

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CONFIDENTIAL
FIFTH INTERIM REPORT
on the
(VLF FERRITE ANTENNA DEVELOPMENT PROGRAM
ILLEGIB
PERIOD s December 1, 1956
to
January 1, 1957
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VLF FERRITE ANTENNA DEVELOPMENT PROGRAM
The following letter is submitted to report on the progress and activity
in the VLF antenna development program for the period December 1, 1956 to January 1,
1957. The proposed methods for the development of a receiving antenna with a band- 25X1
width of 2 kc and a center frequency of approximately 25 kc were described in detail
in a "Proposal for VLF Antenna Development" which was
submitted by
ofl and was designated by
dated July 1956.
ar, I. PERSONNEL:
181 hours
25-1/L hours
136 hours
II. TRIPS AND CONFERENCES
III. ACTIVITIES
A final report is being prepared which will summarize the results of the
VLF Antenna Development Program. This report consists primarily of an analytical
appraisal of the relative merits of the ferrite cored loop as a very low frequency
receiving antenna. The restrictions imposed upon the antenna, briefly, are that it
operate at 25,000 cps and have a 3 db passband of 2000 cps. The basis used for
judging the relative merits of a ferrite antenna is that of comparison of induced
voltages and signal-to-noise ratios with an air core loop antenna of comparable maxi-
mum dimension. Comparisons made are primarily analytical with experimental checks
whenever feasible.
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2 -
The table of contents of the report is given below:
1. Discussion of Results
2. VLF Noise Sources
3. Antenna Equations
Li. Comparison of Atmospheric Noise with Thermal Noise in
Loop Antennas
5. Comparison of Induced Voltages and Signal-to-Noise Ratios
in Air Core and Ferrite Core Loops
6. E-field Pickup
7. cperimental Results
Appendix: Derivation of Induced Voltage as a Function of
Coil Length.
The report is approximately 90 per cent complete at this time and should
be ready for delivery by February 15, 1957.
The expenditure of manpower was greatest during the fabrication of certain
ferrite cored antenna configurations during September and October 1956, and at the
present time has been reduced to a low level. A small amount of data is still being
taken on ferrite cores to provide substantiation for theory prepared for the VLF
Antenna Report.
0
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FOURTH INTERIM REPORT
on th e
VLF FERRITE ANTENNA DEVELOPMENT PROGRAM
PEE OD: November 1, 1956
to
December 1, 1956
W
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VLF FERRITE ANTENNA DEVELOPMENT PROGRAM
Or'
i_ntenna Development" which was submitted by
The following letter is submitted to report on the progress and
activity in the VLF antenna development program for the period November 1,
u 56 to December 1, 1956. The proposed methods for the development of a
receiving antenna with a bandwidth of 2 kc and a center frequency of
a.nproximately 25 kc were described in detail in a "Proposal for VLF
and was Designated
dated July 1956.
a
I. PERSONNEL:
by
144 hours
86 hours
88 hours
II. TRIPS AND CONFERENCES:
None
III. ACTIVITIES:
EXPERIMT NTAL - in connection with the preparation of a final
report, measurements were made to determine the effect of single layer
winding coil length for a fixed core length. The literature is not clear
on this point. Seemingly contradictory results are only partially resolved
by considering differences in specific antenna requirements. Our experi-
ments are based on power output measurements which under certain conditions
are equivalent to signal-to-noise measurements. Results indicate power
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output (at a fixed fo%f) increases as the coil to core length ratio
approaches 1. The effect described by BelroseI for small ratio values
was not found. As a result actual signal-to-noise measurements are being
undertaken to substantiate the validity of measurements made on the basis
ci. power output.
ANALYTICAL - A final report is being prepared which will
sui:narize the results of the VLF Antenna Development Progran. Included
;.: this report will be a discussion of the material and geometric require-
.,,ent s imposed on a ferrite rod antenna in order for it to compete with
a:i_r core loop antennas; empirical results comparing; various ferrite rod
y.itenna configurations with air core loop antennas; a discussion of some
noise problems as they affect ferrite rod antenna design. Briefly, the
conclusions reached indicate the relative advantages of ferrite rod antennas
over air core loop antennas are based primarily on the importance, in a
particular application, of a line configuration over a plane area config-
uration.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
1 "Ferromagnetic Loop Aerials" by J.S. Belrose, W. ?mgr. February 1955
Report Prepared by:
Report Reviewed by:
-2-
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THIRD INTERIM REPORT
on the
VLF FERRITE ANTENNA DEVELOPMENT PROGRAM
i
0
PERIOD: October 1, 1956
to
November 1, 1956
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VLF FERRITE ANTENNA DEVELOPMENT PROGRAM
i
The following letter is submitted to report on the progress and
activity in the VLF antenna development program for the period October 1,,
1956 to November 1, 1956. The proposed methods for the development of a
receiving antenna with a bandwidth of 2 kc and a center frequency of
Antenna Development" which was submitted by
approximately 25 kc were described in detail in
and was Designated.
dated July 1956
I. PERSONNEL:
by
a "Proposal for VLF
160 hours
102 hours
100 hours
52 hours
73 hours
Is
II. TRIPS AND CONFERENCES:
A meeting was held on October 25, 1956, between representatives
of d the contracting agency. The following
persons were in attendance.
1. Contracting Agency
Section head
Project engineer
2.
25X1
25X1
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The relative merits of a ferrite cored loop antenna and an air
core loop antenna were discussed on the basis of effective height as a
merit factor. A model of a ferrite cored antenna which would produce a
greater effective height than an air core antenna of the same volume was
displayed.
tatives of
A second meeting was held on November 5, 1956 between represen-
andthe contracting agency. The
following persons were in attendance.
1. Contract Agency
Project Engineer
2. 25X1
Subsequent to the October 25, 1956 meeting, the use of the
"effective height" as a merit factor was reviewed. If the antenna output
is to be used directly as an input signal to the grid of a vacuum tube . Alr, icy-c
C lP, is
then the larges "effective height' for a given bandwidth is the desired
a~w'lCS ~C'//Pi
figure of merit. However, if the signal is to be transferred to a remote
point by means of a low impedance cable then the power output which can CO &I
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On this basis, the model ferrite loop which was available at the October
25, 1956 meeting is not very satisfactory. The power output of the J
research model ferrite cored device (5 cores 8 inches long by 1/4 inch ?4ele ~ c~
diameter) is 3.75 microwatts whereas an equivalent volume air core loop
25X1
_nk-
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kilocycle bandwidth.
Ferrite cores which were developed by
had a power output of 8 microwatts for the same field strength and 2
were also di s-
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o 'ti
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played. These cores are 15 inches long and 7/16 inches in diameter and
have an intrinsic permeability of approximately 300 at 25 kilocycles.
One of these large cores gives a power output of 3,6 microwatts as versus
the 8 microwatts quoted previously for the air core loop. The general
conclusion that a ferrite cored antenna, even is ?i--a co , would have
no greater output than an air core antenna of comparable maximum dimension
was presented. Thus a ferrite rod antenna 15 inches long would be about
equivalent to an air core loop antenna 15 inches in diameter. The ferrite
rod gives a different package but no significant advantage on power
output for a given maximum dimension.
After this appraisal of the use of ferrite cores in loop antennas,
the customer's project engineer indicated that the requirement for the
hCivieveci,
delivery of a V L F antenna system would be - d