Air Fronts: Air Defense FM 44-8; Antiaircraft Operations Room and Antiaircraft Artillery Intelligence Service - Appendices

APPENDIX I

AIR DEFENSE GRID TABLES

APPENDIX II

GRIDS FOR PPI SCOPES

1. SCALES OF PPI SCOPE. a. The PPI scope of the SCR–584 is 7 inches in diameter, only 6 inches of which are used for accurate range measurements. This 6-inch area is divided into 10,000-yard divisions by a series of concentric traces indicating distances in even multiples of 10,000 yards of range from the instrument's position.

b. The sweep of the PPI scope must be adjusted so that, when using the 35,000-yard scan, the 30,000-yard trace has a radius of 2.75 inches. The 10,000-yard and 20,000-yard traces are at distances approximately 0.75 inches and 1.75 inches, respectively, from the center of the scope. The scale, therefore, is 1 inch = 10,000 yards, with all traces displaced 0.25 inches toward the center of the scope. When using the 70,000-yard scan, the sweep should be such that the 60,000-yard trace has a radius of 2.75 inches, the scale being 1 inch = 20,000 yards with a similar 0.25-inch radial displacement toward the center.

2. PREPARATION AND APPLICATION OF GRIDS. a. Grids for PPI scopes are best drawn on paper to the proper scale and then transferred to the scope either by tracing onto a piece of clear acetate or (when acetate is not available) on the reverse side of the amber covering of the PPI tube.

b. If the grid is marked on acetate it is placed under the amber cover. To do this the frame is taken off the scope and the amber and clear glass sheets are removed from the frame by unbolting the frame from the operating panel and loosening the brackets that retain the glasses in the frame. The amber glass is the only portion of the tube that is used.

c. If the grid is marked on the reverse side of the amber covering a washable ink is used so that it may be readily re-moved. The grid should, in this method, either be drawn on transparent paper or be constructed as a mirror image of a true grid because it is traced on the amber covering from the under side.

3. CONSTRUCTION OF GRIDS. a. Draw the grid used in the AAOR on paper to a scale of 1 inch = 10,000 yards (for the 35,000-yard scan) or 1 inch = 20,000 yards (for the 70,000-yard scan). These grids are extended to cover 8 by 8 inches on the paper. For the spacing of the lines when the Air Defense Grid is used, see appendix I.

b. Determine the grid coordinates for the instrument's position and locate it on the grid. This marks the center of the PPI scope. Draw a north-south line ("A") and an east-west line ("B") on the grids through the located center. Describe two circles, 3 ½ and 3 ¼ inches in radius, respectively, about this point. On the "A" line, locate a point "C" 2.75 inches from the center. (See fig. 21.)

c. Mark a series of points along the "A" and "B" lines ¼ inch toward the center from each intersection of the "A" or "B" line with a grid line. Should a grid line pass within ¼ inch of the center point, the center point is used as the mark. (See fig. 22.)

d. From each point of intersection of a grid line with the 3 ½-inch radius circle, draw a line radially toward the center point until it meets the 3 ¼-inch radius circle. This locates a series of points on the inner circle. It should be noted that each intersection on the inner circle corresponds to a point on the outer circle that has been moved radially in ¼ inch. (See fig. 22.)

e. Draw the final grid through the points located in c and d above. Each final grid line will be in two segments. It begins at a point on the inner circle, is extended to a point on line "A" or "B," and is continued to another point on the inner circle. (See fig. 22.)

f. Trace the final grid on an acetate disc or on the reserve of the amber covering and number the final grid with the appropriate numbers of the area. For convenience, the quadrilaterals are numbered rather than the lines. The number is the first digit of the "X" and "Y" coordinates in that order. (See fig. 23.)

g. Example. (1) An SCR–584 is located at latitude 34° 30' north, longitude 77° 33' west. The Air Defense Grid is used, and the coordinates for this point are ECFJ 0612.

 
Figure 21. Gridding a PPI scope -step 1

 
Figure 22. Gridding a PPI scope - step 2.

For the 35,000-yard scan the grid squares are 0.970 inches high in the north-south direction and 0.804 inches wide in the east-west direction. (See app. I.) The grid, the location of the instrument thereon, the "A" and "B" lines, the two circles and the point "C" are drawn as described in a and b above, and as shown in figure 21. Points are marked on the "A" and "B" lines ¼ inch toward the center from the grid line intersections with the "A" and "B" lines, as described in c above and as shown in figure 22.

Figure 23. Gridding PPI scope - step 3.

2) Radial lines between the two circles are drawn as de-cribed in d above to locate points 1/4 inch toward the center from the intersection of grid lines with the outer circle. These points are marked with small circles. The final grid is drawn in solid lines between the circled points, as described in e above and as shown in figure 22.

(3) The final grid is traced on the acetate disc, as shown in figure 23. The center point and the ends of the "A" and "B" lines are marked on the disc to aid in orienting the grid over the scope. A small circle "C," 2.75 inches from the center point, is marked on the grid to facilitate adjusting the sweep.

4. CONSTRUCTION OF CONVERSION BOARD, a. The conversion board is conveniently constructed by drawing two blank grids in contrasting colors on separate sheets of clear acetate, one grid being twice the scale of the other. Scales of 1 inch — 3,000 yards and 1 inch 6,000 yards are convenient, resulting in a grid approximately 2 feet square. Grid numbers are marked on these sheets in colors corresponding to the grids using a grease pencil or washable ink so that the location of the radar will be near the center. The location of the radar is then marked accurately on each of the numbered grids.

b. The sheets of acetate are superimposed so that the marks indicating the location of the radar coincide and the grid lines are parallel. They are fastened on a board in this relative position.

c. It is in most cases not essential that the grids on the conversion board have the same relative N–S and E–W dimensions as the true grids on the ground. The large and small scale grids can be drawn as squares. New grids for the conversion board need not be drawn for each new location of the radar. However, grids must be drawn true to shape for the conversion board if the limit of a major division of the grid system passes through the board. This occurs only at 40° and 60° latitude for the Air Defense Grid.

d. In figure 12 the coordinates of the instrument are J 0816.

e. When acetate is not available the two grids may be drawn in contrasting colors on a sheet of paper as suggested in figure 12.

APPENDIX III

TELEPHONE "HOT LOOP"

1. The following is a suggested method of connecting a telephone "hot loop" to the receiver of an SCR-543:

a. Disconnect the cords CD-605 and CD-620 from the small transformer C-410 that connects these cords.

b. Connect the cord CD-605 to the transformer C-410 on the side of the transformer marked "headset."

c. Connect the other side of transformer C-410 into the "hot loop" circuit.

d. Connect the "hot loop" to the radio receiver by first connecting the microphones T-24 into the outlet on the re-mote control unit RM-21.

e. Attach the plug PL-55 on the cord CD-605 into the jack JK-38 on the transmitter T-24.

2. The following method is suggested to connect a telephone "hot loop" to the SCR-593:

a. Disconnect cord CD-605 from transformer C-410 on HS-30.

b. Insert plug PL-55 on cord CD-605 into jack on SCR-593.

c. Connect other end of cord CD-605 into "hot loop."

3. Any messages received over the radio will automatically be transmitted over the "hot loop." During periods of silence on the radio, the telephone circuit may be used normally.

APPENDIX IV AAAIS PLAN

1. THE AAAIS PLAN. To coordinate all elements of the AA defense in the establishment of the AAOR and the AAAIS the AA defense commander prepares a plan enumerating the following items. Some items will be covered in SOP and SOI.

a. Sources of available information outside of the local AAAIS.

b. Nature, location, and code designation of OP's, and units charged with establishing them.

c. Method to be employed by OP's in reporting locations of plans. (See par. 44.)

d. Periods of operation for each OP.

e. Locations of radars, their normal area, contingent sectors of search, and schedule of operation.

f. Schedule for I.F.F. code.

g. Type of communications to be installed, the AAAIS and command and intelligence radio net frequencies, and responsibilities for specific elements of the command for installation and maintenance of the wire nets.

h. Personnel required to operate the AAOR, and units from which personnel are drawn.

i. The grid to be used.

j. Warning times to be expected for various types of units of the defense for various states of readiness.