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"SECRET A. D. I. (K) Report No. 527B/1944

1. The operational procedure in the control of fighters by
the "Y" procedure was described in A.D.I.(K) 525/1944. The
interrogation of the two G.A.F. signals officers, who supplied
the information for that report, has produced a large amount
of information on Y-site and airborne equipment which is of
rather more limited interest. The present report, which
contains that information, is therefore being given a limited
2. Captured documents on the "Y" procedure have helped to add
further information, and have provided a further basis for
interrogation; these documents have been forwarded to

3. Four types of "Y" ground transmitter are believed to be in
use. Y-Stations in Germany are said to be equipped with a
four-stage transmitter known as Berta I or Berta II, with an
output of 80/100 watts and a range of 400/500 kilometres, when
controlling aircraft at heights of 5,000/7,000 metres.
4. Another transmitter used in Germany is the S16B (Sender 16
Boden), which is a modification of the FuGe 16, and which has
a maximum range of 250 km. when used in conjunction with a
Rechlin range-measuring unit, or a range of 250/350 km. when
used with the more accurate Siemens range-measuring unit.
5. Y-Stations installed in France employed a Sadir 80/100
watt transmitter, usually also in conjunction with a Siemens
range-measuring unit; the ranges achieved by this combination
were of the order of 400/500 kilometres for aircraft operating
at heights of 5,000/7,000 metres.
6. The transmitter S16B (Sketch I) is operated in the
following sequence of steps:-
(i) Main switch (1) first to stop Hzg (Heizung = heating)
then after two minutes to stop "Ein" (on). Lamps
(2) and (3) light up.
(ii) Select frequency to be used. Switch (4). Frequency
indicated in Window (5).
(iii) Switch (6) to stop Test.
(iv) Knob (7) (blip intensity) turned until vertical line
appears on Cathode Ray tube (8).
(v) Definition of line re-adjusted by means of Knob (9).
(vi) In the meantime operator of range-measuring unit has
switched on "Geber" for production of "Messton"
(Modulation tone).
(vii) Knob (10) turned to right until the luminous area
produced in (3) corresponds to 80% modulation.
(viii) Transmitter now ready tuned for transmission to
commence. Switch (6) to right (Load).
(ix) Transmission is automatic when the switch for the
modulation note is depressed by the operator of
the range-measuring unit; or for R/T instruction
when key for R/T circuit is depressed by the
7. When taking over a "Y" controlled aircraft from one
station to the next, the following procedure for tuning the
receiver and transmitter is carried out by the station taking
over when using a S16B transmitter.
8. As a first step the receiver of the range-measuring unit
is set to the transmitter frequency given for the aircraft.
The range measurer then tunes his receiver to maximum audible
strength of the modulation tone received ("Hörmaximum").
9. The 80% modulation image on Cathode ray tube (8) then
shows an additional bright vertical line within the area of
the image. By turning frequency stop (4) this vertical line is
displaced to the right.
10. The operator of the transmitter turns the frequency stop
(4) until the line reaches a limiting position, and on further
movement of stop (4) tends to re-trace its path to move again
to the left. This turning point ("Umkehrpunkt") corresponds to
the accurate setting of frequency stop (4), and provides a
visual method of tuning the transmitter accurately to the
receiver frequency of the "Y" aircraft.

11. The D/F'ing cabin consists of an octagonal wooden hut
erected on the platform of the receiver pylon; the latter are
of wooden construction and according to P/W, are either 15 m.
or 25 m. heigh, depending on the location of the site.
12. The present P/W were acquainted with two types of D/F
equipment, known respectively as "Heinrich I" and "Heinrich
III". The latter equipment is of recent origin, and was only
introduced to Y-Stations in France early in 1944.
"Heinrich I" D/F Equipment.
13. The aerial array of this equipment, illustrated in Sketch
II, consists of four quarter-wave vertical dipoles arranged in
pairs at the corners of one side of a horizontal frame about
four metres long. In each pair one dipole is mounted above and
one below the frame. Two half-wave reflectors are mounted on
the opposite corners of the frame. A single quarter-wave
dipole is mounted centrally, and is connected to the rangemeasuring
unit situated at the base of the receiver pylon.
14. The vertical axis of the aerial system can be rotated
about the control axis of the pylon by means of a hand-wheeled
drive operated from the interior of the cabin. The vertical
axis of the aerial is geared to a graduated disc, marked from
0° to 360° in a box placed centrally on the table of the D/F
cabin. Readings are made through a small window carrying a
hair line at the back.
15. To the left of the central box is a receiver E16P; this is
the normal receiver unit of the FuGe.16, from which the A.V.C.
(Regler) has been removed. To the right of the box is a
16. The D/F operator, who is equipped with headphones, sits in
front of the box. The modulated note or "Messton" reaching the
receiver is audible in these headphones, and having
established the minimum position, the operator checks the
direction as follows.
17. The aerial is turned out of the minimum position by about
30°, and the reading of the output meter is noted. If, on
pressing a switch attached to the output meter, the voltage
falls, the direction in which the bearing has been taken is
correct. If, on pressing the button the voltage increases,
this indicates that the aerial has to be swung by 180° to get
the correct direction.
18. The readings should on the average be correct to within
0.5°, and for distances of under 100 km. to within 0.3°. This
reading is spoken aloud by the D/F operator, and is recorded
by a logbook-keeper (Betriebsbuchführer), who also repeats the
reading on a telephone connected to the range-measuring unit
and from there to the plotting room.
"Heinrich III" D/F Equipment.
19. The Heinrich III, also known as the "Umtastpeiler", is
referred to in documents issued by "Hochfrequenzforschung
Einsatzstab Holland" as having been developed at the "Flug
Funk Forschungsinstitut Oberpfaffenhofen".
20. The Heinrich III differs from the "Heinrich I" in several
respects. The aerial system consists of six quarter-wave
vertical dipoles, four of which are arranged in pairs at the
end of a single horizontal support about 4 metres in length.
The fifth dipole is mounted centrally above the D/F cabin, but
also forms part of the D/F aerial system.
21. The sixth quarter-wave dipole is placed vertically within
the structure of the receiver pylon midway between the D/F’ing
cabin at the top and the range-measuring room at the base, and
is connected to the range-measuring unit.
22. The aerial system rotates horizontally about the central
axis of the pylon, and the vertical axis of the aerial is
geared to the central box in the D/F’ing cabin as with the
Heinrich I.
23. The D/F receiver used is the El6EP, and this operates in
conjunction with an automatic device known to P/W as PUG
(Peilumtastgerät), also referred to in documents an ZVG 16 P
(Zielflugvorsatzgerät 16 P), and finally with a visual
indicator termed AFN 2 (Probably = Anzeiger Frequenzniedrig
24. The PUG is connected to E16EP as well as to a plug
connection on the central box. The AFN 2 device has the
appearance of a mall box, measuring approximately
20 x 10 x 10 cms., connects to the same plug.
25. The dial on the side of the AFN 2 has a pointer which is
directed vertically downwards when the aerial is in the
minimum position. The correct direction is now established by
turning the aerial a few degrees out of the minimum position.
If the pointer deflects in the same direction in which the
degree graduations in the small window have moved, the bearing
has been taken in the correct direction. If the pointer moves
in the opposite direction to the movement of the degree
graduations, then the aerial must be swung by 180°.
26. According to P/W, this device allows the D/F operator to
fix the minimum position by visual means only, eliminating
errors duo to the human factor when aural methods are used.
Secondly, the device is automatic and does not require to be
switched on each time by the D/F operator.
"Heinrich II M" and "Heinrich II U" D/F Equipment.
27. Captured documents make mention of the Heinrich II M.
and II U; these versions were unknown to the present P/W, but
the II M is shown in a document, issued at Arnheim in May 1943
by Staaatsrat Dr. PLENDL, to utilise an aerial array with
three sets of quarter-wave dipoles and reflectors.
28. The II U, mentioned in another document from the same
source, and dated July 1943, is shown to be the forerunner of
the Heinrich III described above, and to embody the same
aerial array as the letter.

29. The range-measuring cabin is situated at the base of the
receiver pylon, and houses a range-measuring unit. Two types
of units are in use, known as Rechlin and Siemens rangemeasuring
units respectively.

"Rechlin" Range-Measuring Unit.
30. The "Rechlin" unit (Sketch III) was designed by Dr. BECKER
of Rechlin, and constructed by a firm named Graetz. It is thus
sometimes referred to as the "Becker Gestell" or the "Graetz
31. The Rechlin, which is used principally on day fighter
"Y" control stations, gives reading accurate to 1 km.; it
measures the time required by the transmitted impulse to reach
the aircraft and return again to the receiver of the rangemeasuring
unit. This time is determined by means of an
invisible point which travels along the graduations of the
Cathode ray tube, and becomes visible at the moment when the
returning impulse reaches the range measuring unit.
32. The tuning and operation of the Rechlin range-measuring
unit are carried out ne follows:-
(i) Main switch (1) to ON. Dial lamp (2): lights up.
(ii) Knob (3) turned to left (Bright), an illuminated area
appears on the face of Cathode tube (4). This area
is usually off-centre and of irregular shape.
(iii) By adjustment of trimmer screws (5) the illuminated
area is moved to the centre of the tube and made
uniformly circular in outline.
(iv) By turning controls (6) the circular area is enlarged
until its circumference coincides with the scale
graduations on the edge of the Cathode ray tube
(v) Knob (3) is turned to the right (Dim). The
illumination of the Cathode ray tube is now
(vi) By means of knob (7) the receiver in now set to the
transmitter frequency of the aircraft which is to be
controlled (that is at 1.9 Mc/s. less than ground
transmitter frequency). The frequency is given by
the plotter.
(vii) Switch (8) is now moved to down position for
transmission of the Modulation Note ("Messton").
(viii) Switch (9) controlling test transmitter is then moved
to the "On" position. This initiates transmissions
from the station transmitter on a frequency
automatically reduced by 1.9 Mc/s. The modulation
note ("Messton") is audible in the operators'
headphones. At the same time a point of light
appears on the graduations of the Cathode ray tube
(4) near the 13.7 km. graduation.
(ix) Fine tubing knob (10) is now turned until the sound
heard in the headphones is at maximum.
Simultaneously with this adjustment the light point
is seen to travel in a clockwise direction, reaching
a turning point from which it retraces its path.
This turning point coincides with the point of
maximum sound reception and provides a visual method
of tuning.
(x) Phase switch (11) is now moved until the light point
accurately coincides with graduation 13.7 km.
(xi) Finally knob (12) (Amplitude width) is used to adjust
the definition and intensity of the light point.
(xii) The range measuring operator can now either switch on
to the transmitter for continuous transmission by
means of switch (13) or select either an automatic
five or ten second transmission by means of switch
(14). The latter system has recently been
discontinued and on some Rechlin measuring units,
switch (14) and the clock above it are not fitted.
(xiii) To test R/T circuit the range-measuring operator
depresses knob (15). Dial lamp (16) lights up. The
operator must now hear his own conversation in his
headphones. Turn knob (17) to adjust for correct
audible strength. The R.M. unit is now tuned ready
for use.
(xiv) To go over to aircraft control, switch (9) (Test
transmitter) moved to OFF position.
(xv) If "Y" aircraft is being controlled then a light
point will appear on the graduation of the Cathode
ray tube. This gives the correct reading for the
last digit. If, for example, the light point
appeared on the 12 km. graduation, the digit "2"
only is noted. When coarse-control knob (18) is
pressed, the light point will spring forward by 10%
of the real distance of the "Y" aircraft. That is,
if the point advanced by 6.2 km., the correct
distance of the "Y" aircraft could be 62 km.
(xvi) The tuning transmitter referred to in (viii) forms
part of the range-measuring apparatus, and
superimposes its own transmission of 1.9 Mc/s. on to
that of the station transmitter. This results
automatically in a reduction of 1.9 Mc/s in the
frequency of the station transmitter.

"Siemens" Range-Measuring Unit.
33. The "Siemens" unit (Sketch IV) is found on "Y" control
stations controlling night fighters. It is said to permit
readings to an accuracy of 200/250 metres, allowing night
fighter aircraft lacking search gear to be directed close
enough to their target to obtain visuals.
34. The tuning and operation of this unit is effected as
(i) Main switch (1) to "On" position. Dial lamp (2)
lights up.
(ii) Select frequency by means of knob (3). Instruct
operator of station transmitter to transmit (a
tuning transmitter is not incorporated in the
Siemens unit).
(iii) Switch (4) moved to "On" position.
(iv) Switch (5) to "On" position, modulation note now
being transmitted. Green dial lamp (6) lights up.
(v) Tune for maximum audible signal strength by means of
fine control knob (7).
(vi) Turn knobs (8) and (9) until an image appears in the
Cathode ray tube (10). Knob (8) controls light
intensity and knob (9) controls definition of
(vii) Control (11) now turned until the shape of the
illuminated area in the Cathode ray tube is
approximately circular.
(viii) Using switch (12) (Wechselspannungs Diode) and
switch (13) (Wechselspannung Empfänger) the
approximately circular area now made fully
circular and adjusted to a diameter of 3/4 cm.
(ix) Control (11) now turned until the accurate reading
pointer (14) records 13.7 km. The circle on
Cathode ray tube (10) should now have become a
line approximately at an angle of 45° from left
bottom to right top of the face of the tube. If
the circle shrinks only to an ellipse, trimmer
knob (15) is used to reduce the ellipse to a line.
(x) Switch (17) now moved down to coarse reading
position. Turn knobs (18) (Intensity) and (19)
(Definition) until a sharp image appears in
Cathode ray tube (20).
(xi) The coarse reading pointer (22) is then moved to the
413 km. position by turning control (11). The
image in tube (20) should now be a line. If not,
adjust by means of trimmer screw (21).
(xii) This completes the tuning of the Siemens unit. "Y"
control can commence as soon as the receiver
frequency is lowered by 1.9 Mc/s. to bring the
receiver frequency in line with aircraft
(xiii) To take over control of an aircraft the following
procedure is carried out:-
Switch (17) moved to bottom coarse setting
position. Control (11) turned until blip appearing
in left tube (20) forms a diagonal line. If switch
(17) now moved up into up (fine setting) position
the line disappears in left tube and reappears as
a flat ellipse in the right tube (10). On slightly
turning control (11) the ellipse is converted into
a line.
(xiv) Distances can now be read off. The coarse reading
scale is calibrated to read from 0 to 500 km. in 5
km. intervals. The fine reading scale has
calibration readings from 0 to 100 km., which are
divided, according to P/W, in 250 metre
graduations. A very skilled operator is said to be
able to estimate fairly accurately to 100/200
(xv) As the distance of the aircraft varies, control (11)
has to be used to maintain the blip in the form of
a thin line. After the first setting, the coarse
reading is only taken again at intervals.
(xvi) Adjustment of the fine control knob (7) of the
receiver unit as described under (v) also controls
the "steepness" of the line image in the Cathode
ray tube. The position of maximum steepness
coincides with maximum audible signal strength and
represents the turning point of the line image.
This provides a visual check for tuning correctly.
(xvii) The controls shown at the bottom of a Siemens unit
are not touched by the operator. They are set by
the makers of the instrument initially, using
Deutschlandsender transmissions. (According to one
captured document, a special transmission at 1040
hours daily by Deutschlandsender can be used for
this purpose). The controls are subsequently reset
by special test personnel.

35. The R/T set used in Y-controlled aircraft is a
modification of the FuGe 16-Z, in which the receiver unit of
the set is linked to the transmitter unit in such a way that
all signals received on the carrier frequency ("Gemeinschaftswelle")
are automatically re-transmitted on another lower
frequency ("Messwelle"), which is usually 1.9 Mc/s. below the
36. The automatic re-transmission of all signals received
enables the aircraft to be plotted by bearing and range
measurement without any reference to the personnel of the
37. Two modifications of airborne FuGe 16-Z R/T sets are used
in the "Y" procedure.
FuGe 16-ZE.
38. The original modification of the FuGe 16-Z used for
Y-control was the FuGe 16-ZE, which incorporated the
"Zielfluggerät" (Z).
39. This set had the disadvantage that it caused a phase
displacement ("Eigenphasenverschiebung") equal to a reading of
13.7 km., which had to be allowed for in the calibration of
Siemen or Rechlin range-measuring units working in conjunction
with it.
FuGe 16-ZY.
40. In this modification of the FuGe 16-Z, the phase
displacement of the apparatus is eliminated. Hence, when using
Rechlin range-measuring unit, an attachment to this equipment
is used which has the effect of cancelling the calibration
allowance of 13.7 km., and causes the light point on the
Cathode ray tube to start all readings from the zero
graduation on the tube.
41. When the Siemens range-measuring unit is used in
conjunction with FuGe 16-ZY, a second pointer marked "Y" is
fitted in the former apparatus on the fine and coarse reading
dials, in addition to the existing pointer marked "E" on both
dials. The pointer marked "Y" added to the accurate reading
scale is set back (to the left) of the pointer marked "E" by a
number of scale graduations corresponding to the reading of
13.7 km. Therefore, when pointer "E" of the Siemens unit is on
the 13.7 km. mark, the pointer "Y" is opposite the zero
graduation. The additional coarse-reading pointer is similarly
set back to approximately the 413 km. graduation, so far as
P/W can remember.

A.D.I.(K) S. D. Felkin.
25 Sept. 1944. Wing Commander."

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