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zN%ERLM S C I E N l l Z P I C REPORT Contract HAS 1 1 2 - 2 0 7 1 NATIONAL A E R O N A m I C S AMD SPACE ADMINIXTRATION E L E C I P R O ~ C S R E S W C H CENTER Figure I i l l u s t r a t e s the principles of the concept, The a i r c r a f t f l i e s over a normal Marker Beacon signal, and i n so do-, a relay is closed t o activate the cockpit light o r tone indication of the marker signals t o the p i l o t , T h i s is a standard output from existing 75 M c marker receiver, however, t h i s relay, a short series of measurements of actual i n addition, i n i t i a t e s a i r c r a f t height during the time t h e a i r c r a f t is i n the marker beam.
For exanple, the marker beacon receiver relay activates the air- c r a f t ' s W transmitter f o r a s h o r t time and a tone-data signal representing the height as established by the barometric sensor unit is transmitted t o .the ground, The barometric sensor is quantized t o perhaps 100, 200, 3OO,or maybe even 500 f o o t heights SO that height reporting from sea level t o , s a y , a m a x i m u m of 15pOO o r 20,000 f e e t is contained ia a sinple code structure bringing the cost t o a few dollars f o r the sensor and tone encoder. Several of this code (100 quantized elements o r 256 quantized d e t a i l s elements?) have been discussed before.
A t the time the aircraft passes over the marker station is received on the ground from the a i r c r a f t on the VHF the signal I E , rlunicomt* frequency, and decoded w i t h a BTL tone-decoding :unit t o represent the height sensed by the airborne baro-sensor, Obviously t h i s baro-sensor and particularly a very, very low cost unit m a y be j n error, needing adjustment just as a p i l o t adjusts his baro-
Preliminary Drd
sensor manually today.
T h i s is accomplished i n a proposed "proof of concept" t e s t by use of a direct radar height measurement using a ground unit. A t t h i s time an band (modified marine) radar tllooksll a t the underside of the aircraft. W i t h a 50 k w pulse only 0.1 microsecond wide (repeated 1,000 times a second) it 9s expected that more than adequate signal can be obtained by reflections from even the smallest aircraft, T h i s strong signal return i s expected since the radar beam w i l l be a narrow zenith, beam w i t h no ground reflections o r other disturbing radar targets, The marine radar's usual r o t a t i n g antenna is replaced by a microwave horn o r t*pillboxtl antenna pointed at the zenith, The beam i s shaged into a fan shape t o match or improve on the 75 m c marker beam shape.
The radar cathode ray display w i t h special retentivity o r 4,400 f e e t , characteristics i s offset s o that the 3/4 mile scale, represents the f u l l 12 inches across the display, A series of photocells (may choices of tiny ones) a r e placed i n series on a Each photocell monitors line positioned over the PPI s t a t i c line, radar has two discreet distances (now, of course, heights). The ranges of interest t o the t e s t : 3/4 mile and 1 % mile, and by avail- able range switching the photocell signals can represent twice the height values f o r simple tests. One inc of the (12") display rep- of height, It is possible t o u t i l i z e s m a l l resents about 400 feet at l e a s t four can be located per inch and would photocells so that be placed directly over the cathode ray beam (line) established by the 12" radar display (remember the radar is not rotating but i s Preliminary D r a f t being used as an "inverse radio altimeter" so the cathode ray sweep of the screen w i l l be a stationary straight line offset s o that rrO" represents 110" height and 12 inches represents 4,500 feet, o r 9,000 f e e t as determined by the range switch.
Large photoelectric signals suitable f o r selected units w i l l be obtained from the bright emissions.
Figure 1 represents the overall system and shows the photocells electrical. outputs going t o a set of relays ( o r s o l i d state switches) that represent heights. Since there are no air o r ground targets i n -the radar beam area, and the gutput of the radar can be ignored (or gated out) except when a VICF signal comes from an overhead a i r c r a f t indicating it is in the marker beam:-and thus a l s o i n the radar height. measurement beam,8-the r e b y outputs are only electrically activated at the time of the measurement.
N o signals need exist unless activated by the npresencen of an a i r c r a f t i n the marker beam, eliminating many problems of channel- ization, interference, etc.
If 4 photocells per inch are used (could possibly be more, say 5 o r 6 if need be), then there w i l l be a height quantization into 48 units. A t the 3/4 mile range (4,500 feet m a x i m u m range) t h i s i s every 100 f e e t approximately; and at 1% m i l e range (9,000 feet maxituum range) this is every 200 feet; and on the 3 mile r w e These values (18,000 f e e t I U ~ D I U I I L range) it is every 400 feet, can obviously be changed onoe the nproof-of-concept" is established.
Thus, coming from the radar is the 48 electrical contacts repre- senting the 48 quantized height elements.
Preliminary D r a f t Similarly, the VHF tlComm*l receiver on the ground re- ceives the B'PL tone data signal and can also read out quantized height data from the aircraft, About a 40-milisecond burst can provide any one out of 100 possible height codes, using the triple- tone data equipment of BTL, o r two (16 X 16 = 256) bursts of 4-0 miliseconds each can achieve t h i s with the simple dual tone (4 X 4 = 16) equipments, Either w i l l probably do f o r testing purposes .
Now, w e have a s i m i l a r number of wires available from the air-to-ground signal t o be campared t o the radar-sensed height.
The comparison c i r c u i t s merely examine the quantized data and determine if the heights agree ( s a y each is quantized exactly the same, then say wire #21 represents 2,100 f e e t ( a t the 4,500 f o o t m a x i m u m height range)). I f , however, a signal appears on wire #21 from the radar data and wire #24 of the BTL tone data output, then the comparitor recognized that a height reporting error of 3 quantized elements, or 300 f e e t , exists, T h i s i s accomplished by simple relay logic and i s inexpensive t o b u i l t ( c m be done i n house a t NASA as well as the other items), The * signal, provided by the comparitor circuit, i t t e d t o the aircraft;, By use of tone signaling t o the a i r c r a f t , this can be such t h t a plus and minus value i n steps can be transmitted f o r the error data. For example, 100-foot commercially available i f 16 codes were used in the (low-cost)
* Quantity and polarity; f o r example, the error above i s +3OO feet
and the corrective difference signal would be -300 f e e t , cerusivlg the 2,400-foot report t o now read (2400-300) or the correct 2,100 feet.
Preliminary D r a f t BTL tond (4 X 4 tones) system, w e could have a +800 and -800 foot range of error corrections i n 100-foot increments, The p i l o t can be provided a readout directly i n height error and then can reset his baro-sensor so that it is corrected. Similarly this error can automatically correct the output of the baro-sensor i n one of many ways.
Since a l l of t h i s occurs i n a second o r two, the airborne readout would be i n a stored c i r c u i t so that error data i s stored," Error could be transmitted by tone message, such as the morse code, still used in many aviation f a c i l i t i e s , s o that 26 t o 30 steps would be available (actually in 75 &e signal cover f o r about 30 seconds). E r r o r data could be used t o autoqpatically correct the altimeter by a closed loop c i r c u i t (merely shifting the encoder contacts o r the code i t s e l f ) .
Some Needed Lab Data It would be good t o measure some data on photocells as t o their sensitivity t o cathode ray tube phosphorus (good retent- i v i t y ) typically used f o r radar displays. A l s o , it may be necessary t o use some c i r c u i t gain a f t e r the photocell pickup of the phosphor signal so as t o provide power t o actuate relays o r logic circuits.
It i s a l s o possible that the photo sensitive device's output i t s e l f The reason f o r this assump- w i l l be an adequate switching signal.
t i o n i s that t h e radar is r e a l l y working a t f a i r l y close range, by its usual standards, against a rather large target (aircraft underside cross-sections are much larger than "head-on" * T h i s permits the p i l o t t o correct at his convenience and t o note the amount of error f o r replacement of the baro unit ($10.00) if it i s The stored data would be de-activated, beyond the specified l i m i t s .
say i n 2-3 minutes, permitting t h e system t o be automatically i n i t i - ated again by flying over another height sensor, 5 Preliminary D r a f t profiles of a i r c r a f t ) , and there is no other target t o cause noise o r other electro-luminescence of the phosphor of the radar cathode ray tube, Furthermore, some 500 t o 1,000 radar '*hitsEy exist during the brief time the a i r c r a f t is i n the rad= beam.
The tube phosphor "integrates" and tlstores't this repetiti4re signal, enhancing signal * t o noise enormously, Thus the signal-to-noise r a t i o should be very good and the target is only sensed when it i s known that t h e target is i n the beam (via the marker beam signal causing the air- craft t o emit its tone height data).
If the photocell system does not work f o r some reason, then a direct use of delay-lines and typical range-decoders would be used. The l a t t e r is a more direct type of engineering but can be more complicated w i t h the number of range or height outputs and it i s desirable ( i f at a l l possible) not t o cut into desired, or t o modify it, Eurther, there .is a visible the radar circuitry of the height of the target (with the cathode ray photocell display readout) t o the ground observers, and t h i s would be the makings Each photocell would be mounted i n of good visual data source.
its own light-shield box so it is exposed only t o the light source of the radar strobe-line directly beneath it. Adjacent areas would be similarly shielded as they would be separated by % inch.
of the photocells is important but nany exist that The smallness can do this job. Perhaps some photo-sensitive, solid-state devices w i l l give direct, current switching, replacing mechanical relay functions.
* special "$%'oragetubesg1exist w i t h special "memory" designed
i n t o the phospbors, and electrical means t o read out; t e s t s of these tubes i s suggested a f t e r this ear1y"proof of concept" stage where a multiple photo-cell unit i s used f o r economy and expedition. , 6 Preliminary Draft The basic elements f o r this significant experiment are the V I 2 baro-sensor w i t h modified baro-switch plates, BTL tone-data equipment, marine radar (Sperry unit c o s t s about $14,000 t o $15,000 when one considers the offset features, spares,shipping and maybe some s m a l l modification). The "in house" work would be t h e Zenith pointing X-band antenna, photocells, and the comparitor of the radar height outputs w i t h the BTL outputs, The equipments sug- gested should permit a low-cost f l i g h t t e s t and evaluation of the ttproof-of-concepttt type. Since the items are a l l commeraial items, and u t i l i z e d well within t h e i r performance limits, there should be l i t t l e stretching of any engineering, Admittedly, the ten-dollar V I 2 sensor m a y be low-cost, but it can be corrected t o within 50 feet if data f o r t h i s correction i s available in the cockpit during f l i g h t , creating results equivalent t o a $1,000 baro-sensor. Further, the radar would report automatically the presence of the a i r c r a f t , its identity, and establish i f excessive (hazardous*) height errors actually exist.
T h i s l a t t e r function i s now a national necessity even w i t h current SSR baro-sensor units utilizing the 4,096 codes of SSR, The identical ideas and equipments herein described would work w i t h the SSR and should be tested as such, since the ''floating" height references between a i r c r a f t o r ability t o correct height errors e m be fatal i n dense a i r t r a f f i c , Further, the a b i l i t y t o conduct "inflight-calibration" low cost sensor practical, since it can be makes a vew, very *A11 the elements f o r an automatic reporting (of large errors) t o a central point (via land wire) exist, s o that a f u l l y monitored system is possible; thus permitting f u l l use of vertical separa- t i o n c r i t e r i a f o r _II ALL users of the airspace, Preliminary D r a f t corrected at the exact time of its use, in the exact environment of its use, and at the exact height a t the time of the report& w i t h a bell-Jar t e s t every 9 months in a remote, sea level, (not ground laboratory environment).
Radiation Patterns Although the foregoing material explains the principle of the auto-calibration of baro-sensed height infomation, several. questions arise as t o how wide the beams are (both 75 M e and radar beams), whether the aircraft i s in the beam long enough f o r data exchange, the likelihood of two a i r c r a f t i n the beam, the serious fact that the aircraft may not pass through the actual zenith line from the beam emitter because of flight errors (off the VOR track slightly, etc,), The best way t o approach this matter is t o first examine the coverage diagrams of the 75 M c markers. Most 75 M c beams are basically the same, but have some variations i n the minor and The major axis dimensions depending upon t h e i r application, attached diagram from the F A A Flight Inspection Manual i l l u s t r a t e s these dimensions and some tone identity and done code signals combinations now i n use. Typically, i f an a i r c r a f t i s 5,000 feet in altitude, it w i l l pa through the minor a x i s (normal t o the airway direction) i n 22 NM of f l i g h t , or 4 miles duration (see 219 B).
A t 120 knots, t h i s i s a time duration of almost 2 minutes depending upon the sensitivity of the receiver, Since this varies (probably Preliminary Draft on the low side) the time of reception of the 75 PIC signal w i l l probably be between 1% and 2 mhutes a t this height.
If the speed is 240 knots, t h i s is cut i n half (45 t o 60 seconds), and a t 480 knots, t h i s is about 23 t o 30 seconds of time, In any case, the marker signal is present long enough t o a t t r a c t the p i l o t ' s attention and s o that he can hear the tone signals and tone codes several times, Also, this is more than adequate time for t h e exchange of height data as described pre- viously, With increased height the time is greater. However, typically, the lower altitudes have lower speeds so that some compensation takes place, E'or example, at 1,000 feet the signal is 2 miles i n width, o r 1 minute at 120 knots, and 30 seconds at 240 knots (the l a t t e r being typical, low altitude, terminal area speed of j e t s ) , Thus, it i s concluded that a t least 30 seconds, o r at w o r s t perhaps 20 seconds, of signal is available on the normal airway marker, T h i s i s more than adequate t o a l e r t the height measuring equipments and t o assure the radar w i l l measure the most accurate height and minimize rlslant-heightt' measurement errors.
If the aircraft i s not over the zenith of the marker beam emitter (passing through the vertical beam axis), then same means of assuring that a height error is not incurred by the radar measuring that range, Preliminary Draft f f / actual height
Radar heigkt(s1ant heigh9 \
actual - h e i radar and arker transmitter T h i s general error is l e s s than 2% i f the a i r c r a f t passes within 11" or l e s s of zenith, A t 4,000 f e e t t h i s i s a track error of about 1,000 f e e t , I n most cases the flights w i l l be within them track error, i f t h e p i l o t has maintained the s t a n d a d (two sigma) 3- -4.5 degree t o t a l VOR system error j u s t prior t o passing over the station and i f near a VOR at the time of height measurement.
However, at greater distances t h i s (24%") can be more than 1,000 f e e t , and i n f a c t can be 3,000 t o 4,000 f e e t , s o that some consid- eration must be given i n the t e s t s t o w a y s and means of correcting f o r slant-height range measurements.
Crossed-Beam Concept Since the radar microwave beam is readily controlled and shaped a t X o r C band, and directed i n any manner we desire, w i t h the wide, w e can cause it t o provide data not possible poorly controlled patterns of a 75 M c marker beacon emission.
The wide w i d t h of the 75 M c marker is advantageous t o this concept as it assures the tone (data) transmission of height from the a i r c r a f t always occurs. But, w e must assure ourselves that the radar reads the actual,correct height of the a i r c r a f t , not merely the slant-height of the aircraft, By crossing two f l a t planar Preliminary D r a f t beams, each generated by a simple npill-boxrl o r microwave horn (see pages 459-464 of V o l , 12 of the Radiation Lab series), we can simply achieve interesting and most useful results, I" The geometric principles of the crossed beams are shown i n Figure 11, Two planar beams are crossed at 90" (maybe 60° i s better). Each Beam is quite narrow i n one direction and quite wide i n the other, creaeing a vertical t'fanrt shaped bean, Typi- cally, a beam 3" X 90" as measured at 3 db points would be a good f i r s t experiment, A t 5,000 f e e t , 3" is 250 t o 500 f e e t i n radar (beamwidth) coverage, providing about 1,000 "hitstf (pulses) as the a i r c r a f t traverses ( f l i e s through) t h i s fixed beam. It w i l l be noted that if the aircraft is t o either side of the airway, two distinct bean returns exist since the mtennas are merely i n The width (duration) of parallel, both fed from the single radar.
each beam return (count the pulses) is determined primarily by speed. The separation between the two returns (dimension Y ) is related t o the amount of off-course piloting error.
T h i s off-course error is of a track parallel t o the airway direction at t h i s p o i n t , and the crossed beams a r e oriented according t o Figure 11, Thus, if the a i r c r a f t is a goodly distance off the airway at the time of height measurements, then dimension A simple clock running a t the w i l l be lazge.
( t h e units] radar PRF (1,000 pulses/second) counts the times X, Y and 2 i n units of "hits*' and time between llhitsrl. This output is a simple d i g i t a l signal readily processed t o obtain the correction factor.
Preliminary Draft T h i s is used t o correct the actual slant range height m e Since in most cases w e w i l l be de angle ''as'), the corrections w i l l range height (lo4 i s lj?$/O; 20° is 6%, sion Y , i f measured t o an accur error of height of only 1/20 X 6% o r 0.3%, well w objectives, 0.3%typically a t 5,000 feet is but; a 15-foot error due t o the slant range measurement, well within the nationally standard- ized 100-foot quantized system (SSR of 4,096 codes each representing 100 f e e t of quantized height.
Without a crude means of slant-height corrections, some serious off-course errors would create f a l s e height errors. Further geometric analysis of the crossed-beam concept w i l l show that near the center o f the cross the e r r o r s due t o slant-range o r off-track flight e r r o r s decrease markedly because of the rlcosine-functionll influence, It is likely that a vast majority of the a i r t r a f f i c w i l l be on course o r close enough that slant range errors would be minimal, I n i t i a l t e s t s of this c ept can a s m e this, knowing a w i l l be tested as a second phase, However, simple slant correction even i n the adverse case of airway t m f f i c off-course sufficient so as when viewed vertically from the measuring s i t e it is 30 degrees o r i s down t o about 0.7%.
itoring data used f o r vertical separation, rack parallel t o it is a d microwave planes and t eam separation (x/y o r z as viewed f r o m the ground, 12 Preliminary Draft etc,, is still within the quantized values of our national standard.
the higher the a i r c r a f t , the l e s s the slant correction f o r a given airway track error; another compensation aidjng the concept above 10,000 feet.
Technically, the crossed-beam concept is easily installed by merely using two horns o r p i l l box antennas Zed w i t h a microwave "T" from the radar. Crossed-beam t e s t s occur a f t e r some single- antenna f l i g h t t e s t s t o determine w i d t h s , etc, The f l i g h t t e s t s would record w i t h tape, scope cameras, etc., the shapes of beams A and B, their widths, number of pulse "hits", and the dimension Y, Simple electronic geometric correction can be applied t o correct the radar range (height data) so that effectively the data is a vertical line equivalent t o a zenith altitude measurement directly beneath the aircraft, even i f the aircraft i s not over the facility.
Flight t e s t s of t h i s data w i l l establish t h e best beamwidths, angles, and likely errors, however, a l l these values seem well within desired engineering tolerances, By simply determining A and B dbension (Figure 11) i n terms of count of radar pulses (X and 2) as well as Y, then a r a t i o exists between the average of A and B and the dimension Y, If a f a s t air- craft traverses the beans A and B, the number of radar pulses received may be smaller than a slow aircraft, I f , say, a 120-knot a i r c r a f t returns 2,000 pulses, a 240-knot aircraft w i l l return 1,000 pulses since his occupancy of the beam is half the time (under the same Also, Y , i n terms of bemwidths A o r B, i s half, but conditions), the r a t i o of A n o r B/Y i s constant f o r both speeds. mowing t h i s , and the slant range, the dimension Y i s determined in terms of the beam occupancy time and a r a t i o of the time Y and the average occu- 13 Preliminary Draft pancy time (of bean A and B) determines the extent the a i r c r a f t is o f f course and establishes the angle #lan fr vie f the ground site*, F l a t planes must be used f o r this geometry, but it is well known that a microwave beam can be kept f l a t t o 1 part i n 100 (or a thousand), w i t h the simplest of design. The height solution must u t i l i z e this crossing f l a t planar bean geometry t o succeed; yet it i s the easiest geometry t o obtainwith the simplest of s t a t i c microwave an%ennas, The above speed variation can occur similarly w i t h height variation since the beam i s an angular beam and the crossing planes are angular, Again, t h i s i s compensated by the r a t i o of beamwidth vs sector Y w i d t h (angles 0 and M i n Fig, IV), the r a t i o establishing the value 02 the cosine of the off-zenith angle, The same concept as speed occurs if the a i r c r a f t samples are at the same speed but a t The elapsed time of height differing by two t o one (see Fig. 111).
the higher a i r c r a f t (while i n the beam) w i l l be twice that of the lower aircraft. Remember we have exact slant range t o u t i l i z e in our computation w i t h the r a t i o s of A/Y and B/Y, With these dimensions it is easy t o compute readily available f r o = the radar video output, the slant range correction factor, T h i s concept is equivalent t o the suring radar epts of I d W a r 11, ein t h ( i n a "V" config ion) rotated, Here, w e
use a low-co , s t a t i c beam concept and the a i r c r a f t f l i g h t through
IV are illustrations of the 3 dimensional geometry I11 shows that variation i n height s not change the r a t i o , making angle r'atr constant, Fig, IV i l l u ates that the extent of track error varies P and angles M and 0 proportionally
w i t h viewing angle irarr , establishing the cosine correction of the
radar slant range.
14 Preliminary D r a f t the narrow, f l a t beams creates the equivalence of the scanning func- tion of the V-beam.
I n Figure I V it i s shown that the angles 0 and M are equ lent o r proportional t o the angle "a1*made by an o f f course flight as viewed from the marker and radar (co-located) site.
Thus, the electrical measurement of angle rtagr i s the simplest of matters. A pulse counter counts the number of received pulses in the radar video output as the a i r c r a f t traverses the first beam (of the cxmssed beams), that it intercepts, The crossed beams m a y be a t 60° o r 90" meaning that the axis of the cross is symmetrical w i t h the direction of the airway, Thus, the aircraft f l i e s through the plane of the radar beam a t an incident angle of 30" o r 4 5 O causing some effective widening of the beam, but no changes i n the computation of t h e above mentioned ratios. Thus, the pulse c&ter continues t o count during the time Y and then counts again the second beam intercept, Since t h i s counting i s a t the PRF of the radar which is available directly t o the counter input, the counter i s started w i t h the first reception of the beam signal and continues t o count u n t i l the passage of the second beam One beam starts t h i s counter3 signal and no more pulses are available.
the other terminates i t s count. (We could use beam switching and slightly different PR3 f o r each beam.) A second counter counts the number of puls beam & d t o give an average count (improving accuracy since b o t e identical but a pulse o r two might be lost). The outputs of the t w o counters then represent The r a t i o of the counts the beamwidth and angle between the beams, is taken ( a d used t o compute cos a) and they are then reset f o r the next f l i g h t t o pass overhead.
G. Be Litchford August 1969 Preliminary D r a f t OA P 8200.1 C W 7 219-2 UNmPED STATES STANDARD FLIGHT INSPECTION MANUAL 5/27/66 NAUTICAL MILES FIOUBE 219-B Vertical patterns obtained from a Class RM fan marker havlng an impoved type antenna array, receiver sensitivity "High".
FIQ tical fl tterns obtalned havlng a standard antenna rece Page 1 6
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QUBE 219-F Vertical field patterns obtained from an ILS marker beacon. Receiver sensitivity “Low”.
It will be modulated at 3,000 cps and identi- cps and identified with continuous dots at fied with two dots at the rate of approxi- the rate of 6 dots per second, mately 95 two-dots combinations per minute.
A 75 MC d. Bmh Course Marker (BCM).
Where earlier type equipment is installed, marker might be installed along the localizer the keying rate may be approximately 72 ’ back course to serve as a final approach fix. two-dot combinations per minute.
of Marker Beacon Data by Functlonal U s e .
Summary LFR-Station Location ILS ILS ILS Locallzer back courm En route or approach (LFR) FM/LP;\I FM/LFM Approach (other than LFR) , page 17
~ . , ~ 1 : : ; e
-+ data saasor i no t o scale radak f l a t f a n beam Two crossed beams p o i n ed vertically pointed vertically
(abou. i $3* X 90” )
PLAIT VIEW O F CROS RADAR BlXAJ!’E HEIGHT MEASU
a i3
k f
R a d a r output RA.DAR OwfmJT R a d a r output x--e speed, P -track error d e t a i l s of radar output
A e---- F I G II------ B
CONCEPT OF CROSSED BEAMX FOR CORRECTION OF HEIGHT ERROR,.
I...- page 19--- page 200- and direction track error crossed beam radar a plane intersecting the crosssed beams is A-R-S plane A-R-B FIG I11 WSmmqN'T OF COSINE t'arr IS 3 Y RATIO: O F 'BEAM WIDTH AND ANGLE BETWm CROSSED BEAmS crossed-beam radar note that track no. one passes through the crossed beams with l e s s track error than track number two.
the plane RAB i s defined by track no. 1 the plane R'B'B' is defined by track no 2 A n g l e E i s the intersection of the plane RAB w i t h Crossed beams Angle 0 i s the intersection o f the plane R ' A ' B ' with crossed beams "a".
Angles 0 and P I are proportional t o the viewing angle theref ore: angle "a" i s proportional t o katT0- [ A of $ig I11 Theref ore :
radar slant heightX cos ,, I I
actual a i r c r a f t height p i = _ _ I x - _ - - -I -11 a
<2> BTL tone
I
manual r e s e t
0 canned v o e
manual o f a r n i n g xceed-ing e r r o r SOME OF THE MANY METHODS O F RELAYING THE ALTITUDE HEIGHT ERROR BACE TO T1KE AIRCRAFT - ~- page 22---- ___I I - - - - I !2wo aircraft A and E pass through Tiewing the track of B from 90" the crossed vertical beams, (side view) its intercept of Note: A i s 2 units off course the crossed beams creates B is 4 units o f f course I ~- IT I1 Viewing the track of A from 90" Alternate view f o r Fig, 1 (side view) i t s intercept of the two above crossed beams creates angle A PHOTOS OF MODEL OF ALTITUDE ~~~T C R O S S E D BEAM CONFIGURATION Preliminary Draft units off course and B is 4 units I Preliminary Draft 24