ACTIVITIES OF GERMAN ELECTRONICS SPECIALISTS AT MGB UNIT 568 NEAR FENINE: DEVELOPMENT OF THE BROMMY AND WULLENWEVER APPARATUSES

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80S01540R000400090004-0
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 7
• Document Creation Date: December 27, 2016
• Document Release Date: November 30, 2012
• Sequence Number: 4
• Publication Date: September 7, 1953
• Content Type: REPORT

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CENTRAL INTELLIGENCE AGENCY
INFORMATION REPORT
Information affecting the Na-
United States, within the mean-
ing of Title 18, Sections 793 and 794,01 the U.S. Code, as
amended. Its transmission or revelation of its contents
to or receipt by an unauthorized person is prohibited
by law. The reproduction of this form is prohiblted.
SECRET/CONTROL-US 'OFFICIALS. ONLY
SECURITY INFORMATION
50X1-HUM
COUNTRY
USSR ( Moscow Oblast)
REPORT
sualia
Activities of German Electronics
? DATE DISTR.
Specialists at MGB Unit 568 Near
Fenino: Development of the "Brommy"
and "Mullenwever" Apparatuses
NO. OF PAGES
5
DAM OF INFO. 1948 1949
PLACE ACQUIRED
REQUIREMENT NO. RD
FERENCES
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\ I
THE SOURCE EVNui,u.,wi
THE '4011RAISO of, CONTENT IS TENTATIVE.
(FOR KEY SEE REVERSE)
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Development of the "Brommy" and the "Nullenwever" Apparatuses
Method of Operation
Se.
191
a
1. The Mullenwever" apparatus was developed in Germany during the war as qhigirec-
tion finder. By connecting two similar antenna halves in opposition anceIn
proper phase relation, it became pdesible to obtain a minimum bearing of 40.5?;
however, it was necessary to listerr-in on the transmitter for a considerable
time. Enemy submarines subsequently changed to sending messages and position
by impulses not longer than 50 MA) remaining silent for hours and even days.
An instrument had to be deve1oped4therefore4which would be able to receive
such an impulse and immediately use it to get bearings. The "Brommy" apparatus
wqm able to do this but the accuracy of the beaking changed at least 1?. The
instrument described below answered both needs. A switch changed the antennae
to audible reception("Mullenwever9or visual direction finding. It became
desirable, however, to have the two methods work simultaneously and, if possible,
with respect to the same direction of search. This was achieved by simultane-
ously connecting to the antenna four receiver stations, one of the stations
working on audible, and the others, or all four, on visual bearing. (Ste
Attached sketch for a circuit diagram of the "Brommy" apparatus.)
STATE
Antenna Amplifier
An amplifier is located directly behind each the 40 antenna grids (arrays).
First is an input transformer followed by.-an 6A07 tube. Next there is another
transformer, four amplifier tubes (6AC7) connected in parallel, with four out-
put transformers. Thus, a total of 200 tubes are needed for these antenna 50X1-HUM
amplifiers. A switch is located behind each output to make connection either
to one of the four receivers and diridtly to the "Brommy" apparatus (visual),
or to the compensator for audible bearing*,
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N. .47 Orts
PENN Wailagion OkirlhvBea indholied Ay or, Field INstellowtles By "*".)
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Transit Time Circuit
3. Six adjacent arrays were contracted to the input of each receiver. They were
arranged in a circle and transit-time-circuits had to be used to compensate
for the path difference so that the distance between any group of six anten-
nas and the receiver would be a constant, as would the distance between any
group and the transmitter.
Highpass Filter
4. Since the instrument was intended only for a frequency range between two and
twenty me, it became necessary to eliminate the lower frequencies. A highpass
filter was, therefore, installed behind each six-antenna cluster which would
pass only frequencies above 1.7 mc.
Input Circuits
5. Behind the input transformer in each of the two receiving branches (A and B on
sketch) there followed one 6AC7 amplifier, a tuning circuit, another type 63K7
amplifier tube, and another tuning circuit. The four variable condensers were
mounted on one shaft together with the variable condenser for the oscillator
and had to be exactly synchronized.
Oscillator I
6. The frequency of this oscillator was 1,640 megacycles (sic) higher than the
receiver.
Mixer Stage I
7. The oscillator frequency entered the mixer stages, each of which contained one
65A7 tube. The intermediate frequency was 1640 kc.
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Dividing Filter
8. The dividing filters coma next, consisting of four stages in each channel with
a variation of .1. 4 kc in eadh. Behind the first four steps a tube was provided
to furnish a part of the voltage far another purpose (see below).
Oscillator II Mixer Stage II, and Dividing Filter II
9. A second oscillator, the so-called "wobble oscillator", produced 25 kc for the
two mixer stages II which resulted in frequencies of 1615 and 1665 kc. Each
mixer stage II was followed by a dividing filter. The 1615 kc frequency was
filtered out for amplifier A, and the 1665 kc for amplifier II B.
. Amplifier C
10. Initially, a third amplifier was added parallel to the receivers A and B, coming
directly from the antenna and having the same intermediate stages. Instead of
the mixer stage II, however, it had a phantom stage, because it was to furnish
the first intermediate frequency of 1640 kc following the dividing filter II.
Later, however, the first stages (antenna to highpass filter, to input circuit,
to mixer stage I, to dividing filter I) were left off and voltage was taken
from the two divider tubes in the divider filters I (see above). These two
voltages were brought together at a junction point where the strongest channel
could be selected, and from there to a divider filter for 1640 kc, which con-
sisted of the four missing second filter stages, so that the sane selection
could be obtained as in the receivers. The phantom stage which followed was
in turn followed by a second dividing filter fcr 1640 kc. From here the second
dividing filter as well as outputs from divider filters II of A and B came
together at the input of the intermediate-frequency amplifier.
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Phases
11. Calculation will show that the phase of the receiver frequency, which differs
in A and B, can be the same in the intermediate frequency. The phase of the
middle channel C must remain constant, although the phase itself is not impor-
tant. What is important is that the group-transit-time of all three frequen-
cies be kept constant to avoid distortions. In order to keep any error
during direction finding low, the change in the group-transit-time must not
be more than five percent. The phantom phase in Channel C, therefore, is
needed to bring about the same phase shift as in mixer stages II in A and B.
Intermediate Frequency Amplifier
12. In order to assure the necessary bandwidth for all three channels for theIF
amplifier which comes next, Lt. Col. Khazin suggested that an RC-amplifier be
used. This amplifier consisted of six stages with 63K7 tubes. In order to
prevent oscillations it was divided into two parts by a band filter. Its out-
put voltage was 200 my.
Dividing Filter III, Mixer Stage III
13. In the dividing filter which now followed, the three channels were again sep-
arated. While channel C with 1640 kc went through a buffer stage for further
use (and through a phase shifter), the channels A and B went directly to the
mixer stage III where they again joined channel C, which at this point has
been shifted into the correct phase relationship.
25 kc Amplifier
14. The next step was from the mixer stage III to the two 25 kc amplifiers, each
with one 6AC7 tube. Their output was approximately 50 v for the two pairs of
deflecting plates of-the visual instrument.
Visual Indicator
15. The indicator used a cathode-ray tube, type OSW 2068 (Oberspreewerke), with a
diameter of approximately 120 mm. Together with the fader (beam-brightness
control?) and the horizontal signal, the two deflecting voltages gave a radial
beam with a normal direction from the center of the tube vertically upward.
Its lateral deviation was nearly 1800 to both sides, corresponding to the DF
angle. However, the deviation depended on the frequency, The same bearing
deviation furnished ten times greater beam deviation at 20 mo than at 2 mc.
Audible Direction Findink
16. The HF voltage of each array, furnished by the antenna amplifier, went through
a transformer to three condenser plates. Thus, there were 120 condenser plates
serving as stator plates of a cylindrical compensator. At the same time the
rotor of this compensator took off the voltages from 18 stator plates. A sec-
ond rotor collected from the adjoining 18 stators. The compensator had to be
constructed with extreme care. The rotor diameter was 800 mm. The next step
was from the two rotor plates, past transformers, to the so-called sum-and-
difference bridge and from there to channels A and B. The summation voltage
from the bridge was used for synchronization and searching, while the dif-
ference voltage enabled (the operator) to find the exact bearing at voltage O.
The direction was read from an inclined instrument dial.
Difficulties and Shortcomings of the "Brommy"
17. Lt. Col. Khazin especially wanted quartz filters for the dividing filters. The
crystals which were furnished, however, did not prove satisfactory or suitable
for the purpose, although several weeks were used in testing them. They were
of Soviet manufacture, but where the quartz originally came from is not known.
It finally became necessary to use the eight-stage filter circuit.
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4
18. When the antennas were first installed, a mismatching factor of m= 1.7 was
discovered at the receiver input. This was too high for our purpose since it
resulted in multiply-reflected pulses which caused errors in direction finding.
19. The Soviet supervisors were greatly incensed, but they would only allow Dr.
Erich Schuettloeffel one attempt to trace the error on the spot. Following Dr.
Schuettloeffel's directions, the crew had to go through a tedious process of
checking and measuring the distances of the reflectors and the ratio of diameter
to height of the arrays. These measurements were done by the Soviets and turned
over to Dr. Schuettloeffel for checking. When finally the mismatch had been
lowered to in a 1.12 it was discovered that the cement foundations had to be re-
placed to fit the 40 arrays. The Soviets considered this a serious shortcoming
in Dr. Schuettloeffel's work.
uBstioactl-Apparatua for .Ultra High4Atitencyl(Ultra Short Wave)
20. Drawings for the "Brommy" apparatus for frequencies of 20 to 40 mc were quite
rough. No blueprints were made. It was found theoretically that an additional
intermediate frequency would be needed at about ten mc. This reduced the num-
ber of bands to about five to six. The oscillator for the old intermediate
frequency of 1640 mc (sic) had to remain constant. The rest of the receiver
design was the sane as in the first plan. The error in the direction-finding
proved to be greater in the higher frequency: for audible operation it was
1.10 and for visual operation it was ? 20. By using smaller antenna arrays it
became possible to use -mailer foundations for the antennas. It was planned
to use a dielectric for the compensator.
21. The question of tubes proved to be the greatest difficulty. Types 6AG5 and
6SA7 had to be tested for their suitability. For this purpose the German
specialists developed a phase measuring instrument and a tangent meter (Steil -
heitsmessgeraet). The tubes were tested elsewhere with the phase meter. The
6AG5 proved to have a sufficient electron-transit-time, but the 65A7 was un-
suitable for higher frequencies.
22. Only very rough plans have been made for a "Brommy" installation suitable for
frequencies of 40 to 60 mc because it will be necessary, of course, to see how
the 20 to 40 mc installation work out.
Development of the PRD-1
23. The PMD-1 is an instrument which is designed for direction finding of enemy
transmitters in a wavelength range of 40 to 110 cm. It is divided into two
bands: 39 to 67 cm and 65 to 110 am.
24. The antenna is an H -Adcock. Two parallel dipoles are inclined at a45 degree
angle to the horizontal. They are arranged side by side in front of a reflec-
tor and at a distance of 1.20 m from each other. The reflector consists of a
flat wire net which is installed vertically at a distance of approximately 15 cm
behind the dipoles. The dipoles are approximately 40 cm longsand because of the
broadness of the band, have a U -profile opencto the front. At their ends they
are triangular and pointed. The antenna rests on an adjustable base so that it
can be elevated two to five in above the ground. The antenna angle (direction -
finding angle) is read from a goniometer divided into 360 degrees with an
accuracy of .t1?. A 70-ohm cable, with a maximum 1.1 mismatching, leads from
each dipole at the point where they join. A "slide trombone" (Posaune)(Tele -
:moping arrangement) is inserted in one of the branches and must be adjusted
to a predetermined length for each frequency. The signals are combined in such
a way that the phases of the two antennas differ by 180? so that a direction-
finding minimum can be obtained.
25. The receiver is a superheterodyne with cavity resonators. Two IDI tubes are
used as input tubes, one of which serves as the oscillator. The two tank-
circuits are synchronized and furnish an intermediate frequency of two mc. The
bandwidth is 120 kd. This type of circuit provides a reception sensitivity of
3.6 ktbin the center of the band, 9 ktpat 40 cm, and 5 ktbat 110 cm.
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26. The IF amplifier has three stages and contains a band filter and three 6AC7
tubes. One 6AC7 tube works as a peak limiter or as a modulator on the grid-
cathode-path, or as a rectifier in the diode path. Following this there is
a 6H6 as FM-detector and a 65I7 low-frequency amplifier. Finally there is a
1KIP pentode (a Soviet type with 1.4 v filament) which works as a telegraph
modulator at 800 cycles. The LD1 input tube was chosen because the unit is
to be operated either from the line or from a battery.
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27. The main operating switch can be set for the following:
a. Telephone AU
b. Telephone FM
c. Telegraph with modulator
d. Grid current control
e. Plate voltage control
f. Filament voltage control
28. The low frequency potential is read from an output instrument. This instrument
serves for direction finding.
29. The amplifier can be controlled by hand or automatically. The receiver uses
1.4 ampat 12.6 v, and 65 ma at 150 v. A plate voltage of 130 to 200 v can be
developed by a special power pack. No stabilization is needed for the oscil-
lator because its operation is independent of voltage. Since the oscillator
needs only 30 seconds to warm up and its frequency is practically constant
after two vinutes, and since the temperature coefficient amounts to only 50X1-HUM
f= 2 x 10 -/?G, the instrument is very suitable for this kind of work.
Attachment: Circuit diagram of the "Brommy" apparatus. (Army )+, Navy 2, Air 3:
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