I
Inl
33810 OF A RADIO ALTZUVE
18150 ?R3QUW5OY MODUA 1
RNMURD
lew-Lians ft
8.8., ffassaehbusetts lasittet
ogoy
Of 1*0
gabaittod In PartIAl Palfilmuent of the
Requirements for the Degree of
"Aa
OF BSCIANC3
U84&MXBF.TTS UIiTUTY& W1 TISCIOLU
Signatur*8 of Authors-
Departauts of Iletrica1 Vaginawtig
Aeronautical Engine . rig
Octol# 193T
Signature# of Pref essors
I& Cbarge Or R*4, arch
sign~ature of Chairisan of Demtent
Comitte* *a
Gradmate Studeonts___________
MA&sWcjuSrns INSTITUTE0
OF TECHNOLory
FEB J1~
~L01RU~
L
TH1sDSIGN OF A RADIO ALT IEF ,:7,
REQUENCY MODULATION Tr
.ligNG
by
Shih-ng e L in
"TI
Nl
ITLiraries
Document Services
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2
October 1, 1937
Professor Geourbe W. Swett,
eeretary of the FaOulty,
Massachusetta Institate of Technology,
Canbridge, massachuastts.
Dear 51rg
We hereby submit the enclosed thesis entitled
aThe Design of a Rao Altimeter Using ?rqgaency
Eodul&aLin MethodN in partial fulfill
ant off the re.-
quiresents for the degree of Master of Science
the
assachmsetts Institut, of ?echnoloey.
Respectfully yours,
Ieu-Lians Wu
Shih.-Nge Lin
free
3
the
authors wish to take this op;o4tmnty to ezpress
their gratitee
assistaas
and deepappqreUtaes
and suggestices rendere
Prof. C. 1. Draper aAd Prof. W.
for thb lvauable
b Pret. E. L. " eles,
. larrow; als
to Vv'.
Azold Peterson for the persission to copy his hi
oscillatr'
desli.
To Mr. W. f. Cook of th
4eusavtleal
Lndebted for his coastat help
Departt,
we fee
a making the ezpewletal
appaatua.
To . Y J. . Liu, we express our deepest appeiatie
for the discussions ea the theor
r
fial
dei.lp
I. L. W.
8. L.L.
4
TABLE OF CONTENTS
Page
1...........
Title
Letter of Transmittal
U
.................
........................
Acknowledgemnt
*
............................
Summary
6
e**eBOC*
8
.........................
Ittredwation..
11
Review of Absolute Altimeters ............
I Mechanical
II
III
Sonic
11
....................
12
...............................
14
Electrical .........................
Preeaminary Design and Experimeats
...........
50
Theory e.......................
General Considerations ..............
56
The Transmitter
58
The Receivers
*...............
42
.......................
The Frequency Moter
46
..........-......
The Frequency Modulation Systen ....
o,
The Parabolic Reflectors ............
60
Description of Experimeats ..........
62
Experimental Results ................
ConelAsion ...
Discuissions .............
....
......
66
67
3
...................
Page
Final De.sg
I
II
III
IV
V
Appendiees
?.......a..................*
..
General Principle .................
73
Discussion of the Theory ............
77
Seleetion of The Parameters
87
.........
Discussions of The Final Deai&n
......
.........................
.........................
99
100
.041..................--.--..
Tables
Bibiography
96
98
9....................
Coaclusions ...
Photographs
.....
..........
..............
108
6
To
desisa a praetl
al radio altiaet~r rar neasur l*g the
absolute at~tu6o or an airplas. above the gwomdw
Anw? a @atefui stwi of SeW prop""d absolau alti.
Seters, a brIef survey alaSsiis them Into three prinelpad
YOU) 6sia meoeale
5 *ad 9 "we
4wea~s.
ptb*Lmepgl
NNW
@V@ ee4 as to Wbeir sAvaatag"
eola attewa
has bee. "it
of radio a~lees
~e~i#-.am~te.'.
have bee. melewal
4
et rawiQ altte
Owfereat baste preLspla.
A the"" based as thM beat twaelsf
etfleet
to the kropese
~-&lm-qi-ef
Ser tffeset qrsta
u ty.
ieet am
raoie wavais tvva lftumeay u~iaLatloa
eet4.a or abeue4i
Whs thewry
t"e
ALsOMMaAse
*s~
*ad 415.
t as ujtw*4aUe
a
ad
therewslayloD
*wqueaey short-mve.
tesasltat~SeaYeles) set & woSiVtFr as valasafe.
quemmy inodulater a4 frqueaq
ftwe'rismuts
e&"
ap
w~avse"
aster have heas des"Lbed&
were Illustrated with phat.
graphs* 2he experlnautaI results we"e toie4 to be masplatnabU
7
by this theory.
was
As a conclusica, the preliminary design
not mnoessful.
Finl
nDalans
Ire. the experiene4 l&rned in the preliminary 4esiga,
a aew theory founded as the standing wave effect, using OS
asetially the same apparatus as in
wae d*eloped and thercumhy dcussed.
the preliminary desi6a,
heOretical gharw
aetOristic curves as well as control-ing desta evnstants
were draea.
It
*perilental
results ootained in the preliminary design and
was founa that by this new theory, both the
the SuCegs fully experimeitaIl results publighed by Mr.
"tu
were satisfactoiLy explained aau theoretical predictions
agreed remarkably.
Iu enelusica, a revised final desiga based e
theory
was
presented.
It
eas reomameded that
further
the mew
Ox-
pealmeatal confirmatios of the new theory will lead to a
prastieal desiga Of radio altimeter of high eomerotal value.
8
Ua the 'rts~l
JU440at Of a Skitlled pilotL Is tet.
epto4 by bad wathbo ~~t
e the oweeary eemtinum"
-mi-yI4e or tbv aititude or m ia"
1.vTO
&n.Ve tho 6"N"
Aks~t aepand Iap~b ULatwiuat seauwma.
As an lablicator, tb. ganoraiA4 ua*
simple and JUMh
braetria alitimeter suffers tkte fol4owift,
(I)
it
eu~Lter. tim elbvatics above a&.0v
tba asls t AUtLtd *at a SIwpjaa awo
9"1 l e~vatica of the groamd ab*Ve$ 6"
(a)
eoowh fer
(a)
defeat* la jl .
the
9o "t
hM gpome *Urfa"e
level a&e b&*M*
o4~lftyT IfrtVow altlAwpter Loasot SmISOtive
a*nfo laiang "4ratlte Ia bed wISIb"It4.
fte
Iaxift sI'satlceo
iserolA type altimeter
elsa Ives yowl... ~zwrea* pu'tloI&ry st low altit&ndea
Therefore th* nec~saity of an absolat. aItiweter wbich
give* the altiude direatly above the guamd
of the teirala beneath has delves mny
&nd I"*peadet
ezperlsninters Le In#*
vestigate the vita"I probimas
?r~ a areful situd1y of the paist pub iat
ices# it was
fowl that thar* ewe prinaipaluy tbree saaerai types or nip.
solute altinsterw; afsmeh. sebaialD sf-ic and *leiaJ.o
U..iwr, the pr*eat tweae toward tho flasA. solitica of trits
9
probles lies an the improvement of the last two possibilitiess
(a)
the gsnic altiaeter, utizlaing reflection phenomena
of sound waves.
(b)
The radiL aitimeter, utilizing reflection of radio
waves.
Up to the moment, a number of investigators have been
suowesstul la produeing practically working Lnstrua*ts of the
seale type, yet very few of the esperimental results frea the.
proposed radio altimeters ea
show satisfactory cesequuaeoe
In the airplene.
esewver,
in Ub
the possiblty
fature to overea
In the saet
grat
the present disadvantage
type, namely,
praetical applieation,
through the rapid
for the radio type altiueter
encountered
the bulkiness, the short range of
"nd probably the ese
weight, Is very
evelopmaet of ultra-shert wave
tech.
atgn atilised 1a radio altimeters.
tt is the purpe.. of this thesis to derive a most satisfeatery theory for the radio type using frequency modulation
and to desigA an altimeter based em this theory se that It
may
overeone the present disadvantages involved Ia the sonic type.
EvidAetly, the fate of the radio type altimeter depends
upn further investlgaties of the skillful applicatica
the developed theory so that a practicable apparatus
worked eat.
*f
am be
Rceommmaticu for a progra of Ntur* rustarcho8
is
prluz~ipal.iy basod on experiences drawn frcu prelialnary Inl.
vestigation.s
11
aEVlE
While few
practicable saa
noters have bte
demonstrated,
R
ALTIMET
OF ABS 0L
1
sa isfaetory
a,
absolate ati.
laooratories aW experl.
seaters have engaged in their developseat.
The means of attaei
were as diverse as the number of researah workers.
Videly
dtaferent statements have been reported as to the success at
their mdels.
This article will review briefly acme
moat iaportant nethods an
of the
results obtained at preenat.
In general, there are three principal types ea absolute
altimeters# naaely, mechanical,
snie and eleetrical.
£I echaicals
(A) basic principlea
To time the fall of an objiet from a airplane to the
gr und.im
(3) Metheos used&
smoke pots or torpedoes Dave been the sisales employed
and a stop wateh or slailr
a siaple, saal
device does the timina.
radio oscillator Las been constructea La a
bomb shape and the impact of the &rid
by th
leased sechambally stops the transmitting.
val of OsillLia
Recently,
is
bomb after reThis short iatere
In4lated in a radio detector i
the
plane.
(C) Disadvantagess
1. By using smoke pots it
is
neessary to se
the
12
grouma
in
order to observe the burst.
8. The airereft engine has to be extremeLy quiet so
that the sound o. torpedoes exploding aen be heard by the pilot..
5.
variatic
The correct tining of all bomb types is
subjet4d to
of weather ounditions such as wind velocity, air
density and pressure.
4.
Not eoneaoically practicabLe.
1.
Not practical for easeedingly low or hI~h altitude.
(D) Puture Possibilitie&I
The scheae has a liited
appioaticn (not suitable ia
a city) sad appears to have no great possibilities worthy of
fature developments.
U15Son1c6
The preseat knowledge concerning the developmeat of
senie altimeters is
best described in Teeanicaa Ntes, 39g GI,
N.A.C.A.
(A) Prineiples
the Aethod of Measuring the absclute altitude Is based
on the rate of travel of somd -waves.
A sendermreolver com-
binaties able to produce aeoustie signals ad definitely to
detest the corresponding e*bes Is
The time
instaleG In the plane.
interval between the sonding of signals an
the
receiving of echoes indicates the altitude.
(B) Ietbods and Emperimental Resultas
Nore than twenty known methoas have ben used and the
13
*xperiaatal results up to date give the following SeacusionsS
. A inbewr of seale altimeters have bees operated
matistfoUrily qp to a a.a
aLtitsee of a0
feet Under
airplane ewuislag *oaditicas.
5. For
iAding fl1ght in airplanes, the maximns aI-
titue will be double that for crusiagf eeditioas.
In al.-
is approximately thre times hgher.
ships, it
U. The amimum altitwe seasurable is abct tea feet.
4. At preest, at least five o
e eal seate atlmeters
are em the market with a ainiatanstallation weight of 60
pouads ad maxima Useful altitude of 00 feet.
(C) Disadvatage
ad Difficult&e.
. maimum altitudemeasurable and ainiaan weight of
iastaliation limit the practical use ti airsbips and large
troasport pianes.
U. The maximma operating altitude is limited by the
engine noises on the aireraft.
3. Urors due to buoldity and temperature effects e
st uad velocity and errers from aircraft speed ate
be acre setrious than high frequency
iberly to
avs uset Is radio al.
timters.
(O Ntmre peasibiliiess
etwlthsteaimg the present difleulties eAeUbm.
troed in sQ&iU altimeters, the future possibility of the
final sclatioa of asholate &ltitud. aeasuemeat by sent
14
method Is very great.
The Pblished experimental results
The
are such more anwmrwos tham those employing radio waves.
rapid improveMents in this type sow a tend~emy of immediate
future success.
IIElodtrical
The elctric&l art has offereda rich field for
lnvestlgators to find the soluties for an absolute altimter.
Nearly
all aodels Involve the adapttte of ultra-bigh-
freqsacy currents.
I& general,
It
ga" be Classifie4d into
the wtilization Of capaitty effect of radio frequemny eurreats
and the reflection p1-114M of rauto waves.
(A) C&PacitV Altimeterst
(hefrenao
a)
1. Principles
The capactty of an electrieel aondest1a6 system
changes witb any alteratios in the relative poeition e
the
parts ia the system.
B.
Experimental Resultas
Qee of the successful types called Gum Altiaeter SheM4 that satisfactory performanoes are limited to
100 feet Or less, and the sensitivity is very poor above tais
5. Disadvantas
the maal
range of indicatica attained is
of the order of 100 feet which is too low for most purposes.
15
4. fNture possibiAtiess
By applying the recent developstint in uatra-ighfrequeny, tobique, the oapacity effect can be inreased to
such an extent that practical applicaica may be possible.
(3)
Rladio Altimetersi
Nearly all radio altimters utilise the refleeting
pheanmana of the eletro-magnetic
At present, only a few
tave.
The metods and
experimental res.ultz have been published.
apparatuo employed show that the experimental stage has
r~eent radio altintor
began and for future commercial practice,
desoig
typ.
is lagging behind that of the s"ic
the laat three. yeaxs,
an*ay patents in
just
Iogver in
this field show that
strictly confidential investigations are being carried on in
Fellwlng
the United States as well as in foreijia mc.uatries.
is a list
of the advantages of radio altimeters that ar
eeno-
sidered suprior to those of the sonic type.
1
Radio waves are not disturbed by airplaa
engiae selse.
S. Errors due to weather conditica,
sach as
wiA velocity, atmospherie temperature, hamidity, etc. are
likely to be less serious than in sonic attimeters.
5.
Radiation power of the eleotro-magnetie
wave can be obtained with uuch higher effetiency and greatw
eemvenienee thaa that of sound waves;
C
with
-
16
suitable output of the oeillator,
a useh higher altitude, of
several thousand meters cam be measred.
4. The power supply of nearly all raao altimeters
comes from the same installatioa which is required by all
modern airplanes equipped with two way radie ceemmieations.
Consequently,
the extra installation weight encountered in
radio-altimeters is maost likely to be much easi.r to. reduce
to a practicakole quantity.
5. Through the development of wltra-short. wave,
the spce. required for reflecters and antennae is going to be
such less bulky than the meshanical parts of sonic altimeters.
From the above cinsiderations,
the future possibility of
a final solution of the developtnt of radio altimeters is
more
wospecti e and optfibstic than that of soaic altimeters
although the present available experimental information regarding this type
A didst
twe basie
is sare,*
ed
of the suggest radio altimeters wil
show that
principles have been tollowed, namely,
1. The cyclie cbange in the phase pattern of a standing
wave after reflectic.
2. The time interval taken by the radio wave to reflect
back fr a am object.
In order to have a thorough understanding et the theory
adopted in the design of a radio altimeter using frequency
17
aodulatioa, a careful review of the suggeste
nethods basing an the above principles is
l.
Theoriesssoed
and methods suI
and pLatented
very helpfl.
for bwil1ina rad_*
altimtera utilizIna th~e crain shae shange as ~a inica~ion
Consider a train of waves movia
a reflocted wave m:ves to the left.
place,
to the right while
Interference wil. take
and the resultant displemaLnt of the mediam at a given
point and tiae will be the sam of the InA iviAuais
In
intervals
1
p'laceents.
fig. 1., the positions of the waves at successive
Of
1/8
period are plotted.
I$ eas be soon that there are always points of ser
displaeement N at intervals of balf a wave length.
Half way between these points, at L, the Waves will
always mst in the sase phase
&adthe aislacement will be
18
a Maaimi
the former poititas are *a!led aedes,
the latter
loops or anti-odea. Disturbanues of this sart are called
staiding waves.
Free the abve
comsidewationa,
tranwatted and the refleeted radi
It is elAeat that the
ainals (f
wsae length 7?
will give a standing wave pattern as showa la f(4.
It
ea& be seea that a receiver at an altitude erraes.
po4 to eatl-mrnde. sa.e will give a maximm curreat ldUatiem
Wiile at mode saae will give a
Ihis stanudg
Osteent
ma1
wave phrnemeas is utilsed is
indiatLon.
mways as sa
alJtitde seasuremsst.
A
A general method as described I& Refereea*
.
a. Pr iciples
ftanding raai
waves ar
prodaeed by reflectica
fres any eoAduetIve refleetlag object whes radio freqaeay
ergy is radiated (reM
the airplas.
The modes Saa leepS
of the standing waves predmOAd by the Wefleet.d
eA
dire*t
waves is detested by a reeniver 40 the plane, thus giving a&
iadioatim
of the altitude of the plase from the grOem.
b. Disadvantagess
It
effeetive,
it
is obviems that it
must utilise Wave
suh a system Is to be
egths of the Oder Of a"*
peters or acre, beeasse any attempt by the pilot to .*eet the
mew of aedes or leops of the standiag
passed while aseeadlng
or
wave *hich be has
deseending resuLts LA comfusios, die
19
to the olse
spaeing of the said modes or loops.
The see of MW moters requires a bulky aatena systee
and In addittaa the avaiUable frequencies in this portIca of
the frequeny spectrum are eongested, so that interference
free other stations may cause erroneous readings.
Jeg
Utboas developed by E.
(Referenes
P.
W. Alexandersoa
4, S, 7, a, 9)
a. Principles
If
the time Interval in units is
measured equal
to the time of one oscillation or eycle of the antomna current,
equal to the number of wave
the timeu interval of the eahe is
lengths the refleted wave has travelled on Its way from the
antenna to the grcsmg and baeh agaia.
If
this distasee is
varied by an amount which Is a fractica of a waye.-length, this
variaties wIll sualfest itself
Ia a variation of phase of the
returning i7ave relatively to the phase of the transmitted
wave.
If the distaace is varied by an amount of several
wave lengths, the phase of the returning wave will go through
the cerrespoding anmber of eyelie changes of phase.
Thus it
we have means for asertaining the phase .of the retwring
we
waveand are able to ecmt the numo er of eyc.ie changes, we
are thereby able to make absolute seasurements of the height
over the groud.
A dircot measurement of the phase of the reflected wave
In relatin
to the transmitted wave is difficult.
Nwever, it
20
Was
that the refleeted wave modife
diswred 1W A*exars
the freqawy
&wave.
fe the origna
well as the phae
as
is dependeat m the st"ath
The ae 1& frqsy
eftleted wave.
of the
the
sae fe
these
as followe
e*anes of fregeamy is explalm
A* OsIllater will os*ilUate at its natur&l period osly
wheM tb
foree. WkiIh A"
reSterlt
ftR
o0t sie,
these fOeweS ay a4d to 4w
sabteset free the Sabereat restorwg
the resultaat restoring foree
of the o
2bs
Ullater.
it
tore*.
It
is,
however,
obIk deteranes the actual perid
the forcta coing from
utsUie Is Ia
phase with the Iabereat restering fore* ad inrease It#
seillator will
ellate
is
UhSm the Oseilate
itself are the oSly Oes thetmexist.
ated Go by foW0.
1n the esellater
@aaa54
the
with * bigbr frequemey, and Wise versa
This eyelle variattA6 at ftreuemey was atilised bf
Alama
rses is asaseng at~iud
se$t
agtheds
be
The dtail of the metheds use
referomees 5, 1,
6
la geaai,
are best desorlbed ja
the eyelie variatios of frequenya
of the seinlater duo to the effeet of varyiag altitude is
masured by beeting with emother eseillater of oanstant freqmey
a4 the beat freque.ay .bteimed is seaarue4 bf a frequmey Seter
I terms of *yel*I varyltg eurreats.
*. Results ObtaIaed
Experimetal results have been obtained Is flight tott
21
up to an altitude of 4000 feet with readings at each 1W0
feet as a step. A comparisoa with the readings obtained from
barometric altimeter shows fairly goed agreemenut.
4.
Difficulties and disadvantages.
4.1 Special attention ana expert interpretation are
necessaryo
4.2 Not direct indication.
4.- Too many apparatus needed so that excessive
weight and bulA prevent its
being used as practical altiweter.
d.4 The long trailag antenna used is inconvenient.
Methods suggested by P. 0. Patterson
ja
5
(References 6 and 1I.)
a. Principles
This is
an improved application of alexandarsents
method. In the latter, a heterodyne beat note due to varying frequencies (which is due to varying altitudes) and
other oscillations of constant frequency has been used. This
beat note is then supplied to a frequency discriminating
circait and rectified and caused to control the indicating
device.
Bowever, Ly PNtterson's improvement,
this indication
of altitude is produeed witUhat resorting to any use of
the heterodyme beat principle thereby avoiding the necessity
for an indbpendent source of oscillations and other equipment
necebsry to the
se %f that principle.
22
AMth r methd L# to have the eaillationas enItea
the Laten
la
to be eaued to vary in awplitude as the eraft
Changes ia altit
The aaplitude of these variatios being
e.
utialeatly great to pemit their translatica dl~etly late
iowications of altitude,
b. methods used$
The above principle Is accoaplishe
by adjustig the
frequency of the osaillater to be slghtly differeat fro& the
natural frequency of the antenna eircuLt.
Thb
the antemaa
circialt and the oscillator eireuit form two eopled Indepeadeat eireuits.
As the altitude varios
bears a varying natural period.
the main escillator
the antenma circuit
Throuh the couplinj betwe
lircuit and the antenna cireuit, the an.-
tenna eirouit gives an e:uivalent varying lead in
thfaain
usaillator circuit so that tke osUilltica aaplitude aa4 I&
tura, the plate current of the oesillater is
a fumctica of al.
titude.
0.
Eperimetal Rbta
This result is deaeribed in retfereseo
G.
Itgives a
warning device at ON feet and IOW feet of altituse with the
ooaplete lnstallatia w.ight of 6 1/2 pounas.
d. Disadvantagess
1.~Diseoatinwusa
inaAcation.
2. Long trailing antenna.
&. Only warning signal at certain altitude .s
provided
23
WLUW(Mt SiViLJ4 r*atty at OtMeV ittkJAU41
SMUtho"
lzk.)
(Aeferewc
by4 To Js Boraor
This is n~o more than aa Improved way of A.tectlat
the altitude by measuring Ct~k relative phase betiwea La traanitted and reflectedi waves.
The phase abift by refiectliag a le~t 4av. (IbOO meter)
Is aecospliuied thr~' gh the~ md~1im of a carrier wav* of ultra..
bik-frequeacy so tbat the sum*e pbase wmamuresamt *&a
rvache4 withcut tht. uisavantaes
bo
4 usin4 bul*.y aateuria aad
undesirable iateirferewo.
be Ntkkoa susoste4.O
fte
ultra-highkrequowy is aoduiateo or
wbLledi at a comparative~ly law freqiieacy,
sarnL as U(Mi tc,,, 4
the altitude ij-dicati~u is obtained by measurLm
difforen
betvwen telc
tbo V""s
cat and wtieoted MOOi to* acaqwumits
of the u~tr&-Jwibtwr~gemoy *eirgy.
As deserited Inareteremee
I** phase abifteErsO bah*IMots, cuuplturs, etc* are U&I
C. RzperiuetaJ. kOsilts
Noexperileutal results have beat published or
are available.
to Disadvantages#
I* Altkwu%,h the *UltituI
tV be
inl'.cat.1aIs
be lie~ved
CL~tiUUUV tk* scale IS 114t lIAQ~~r avnd aspeeiaii 'in.
24
aw at b*Uh h1k &," low altit"0s
r.liabl. z'faAti-s
go Toe sueb apparatuas r; .4uireQ so t~t
*m.S&AiY
weigut is aee.sawyo
laA tbA4 ae .iiby Ll keaJAehifi4 (Ie*reuo Lro.)
Altkhc . It Is 4ecribvd kW bpenshie
that bU
as th
pwia.ipl.
nettogd of deerminlai the altitwie Is beo
fT aiaurift
tth* tice
I.*y tf the ref~te*t
with
U,.,
respect to thet ditect ways la actuality It is pwtm..wilr
tcou&W
d.1ay as caa
c the pb&.J*-shi tUMi rather than tim
be man by a oXc,** examilat~ca or tMe svgestet
~aSbbhl~
1Fq Isa A
UOt the ISOM 'beat tre1
C4~ hU
incrrect saise., is
method is no nae
*thoa*
ZMa
a wPt*tica
ve already bema 4.v.)op.A*
of the ptnlla ho
Sim*e the astods sitgostod beta aumuaese
alytkw sam as the autbors, a moro 4etaU.4d t18soma4e
go~ publisk*4 experimentl results are ava
b~l.-
do Advataes aM ODiadamntaiewe
See
te
eaclusiao
~.Tkoowies ;;md lethets sugsted tor bt A-if
Radio
Atinoet.s atUilait the time Interwal take% by ths radio wave
25
to reflect back an indicati n of altitude.
1s a well kaowa fact that electro-mgnetle waves are
It
velocity of ight,
traVelling at tb
Referriu
to fl.6
i.e. g x L0
u/4.
,lt
R 0 Eeight of airplane above groAnd Li Seters.
a idteane between transuitter and reeiver
D
in
eters.
* a Velocity of light in a/see.
Then the time taken ky the diaret wave to reach the
receiver is
aad the tie
taAen
y thbO reflected wave is
tb- 28/a see.
The time lagging of refleeted wave by the dizret -ave is
ta t2 W , a(2R-Swa
am** eithew the time laterval taxe
ave, toe
the ts e la"gin
by the "flet
of the refleeted wave behinA the
direot wave is a Usea"r fuastio
of the altwitue an
StiUsed as an indicatica of aititude provided
at
ted
sa
be
aUitable seaas
wtdh
be*er, we aust aohnowledge the fact that this time
26
interval is extreelr
at g
==U=0..
80.
* ilea - (3S00e)/(az
so that aoy attempt of measuring it
S z s-*ee.
W
OSs)
by direct method vill be
a fail*r sine the acat soasitive tiining lastruweat is 5 at
preseat, Ltmited to I x wsee.
Only Sadiroot means can be
used.
I.1
Sethods smggested by
c.
(Reference 1i.)
3. Terry.
a., ?rlacipies
ralo ftvqueaey sigualling system whreia
a high freque.ay is generated interaittently and seans out
lapes.. frea a transitter, which ixp@Laeo strike the earth
fre
*hioh they are retleted baak to a reeiver.
is operative e-ly ew
aImpase is ast
The reseiver
by the' tramaittor.
A indicater sooperating with the ree.iver end transmitter 1s
aetuated ely
by refieeted esre to Ininte
the time the weVe
used in travellung from the trManittea to the earth and tow
turSang t4 the receAver.
b. :ethods foeds
A very high frequensy is keyed ky a seemd
osillIater at a eonlderably lower frequeSoy so that
Ay a
few eyeles of high frtqueny energy at a time are radiated.
The tramitter at the sane time cbarges a condenser whieb has
arossing its terminals a suitable resistaaee.
This resistanee,
when the transmitter is Ia space, discharges the condenser
at a predtermianed rate.
A receiver sNOcent to the transmitter
27
Is provided with meas coatrolled by the low frequency oacillator for readering it
inoperative when transitter
Is oper-
ative thereby preventing the transmitted energy fro& directly
affeting the receiver.
The receiver readered operative by
the refloeted wave furthr Ascages the condensed unit.
Consequeitly, when a transaitted wave is
groad and reaches the receiver,
refLected fr o
the
the coadensr will have a
charge d6ependat an the 1ength of time between the cutting off
of the tranmitter and the reception of the reflected wave at
the receiver.
the average value of the *bare an this een-
denser Is utilisxed is
an indicati.n of altitude.
Several
modiflid methcdas have been maticned in reference 13, although
the nature Is just the
same.
a. ExpeWImental Results
go published results are available.
d. Disadvantages.
Although direct and coationaus indiestica of
altitude any be obtainable,
it
is
believod that the excessive
units required as described in referen=e 13, vill
give an e*x
cessive wieght as mell as balk.
g
Dethod used by S. MatsUo. (iteference 14, 15.)
a. Principle.
The principle iavolves the time interval,
thereby the beat frequency of the tr ansaitted waves on their
28
path to the dateetor as gewerated b7 frequency modulation
of the oscillator.
This idea was developed and ewplcyed in the preliminary
design of this thesis without firs, knowing that it has been
aeationed and used by Matsuo.
Iowever, frou a *ore detailed
dissuasion later, it shows that tAis theory will involve a
frequency modulation which is also utilUad by Er.
as phase
shifting effeetg and it is
that the steading wave offct
Aspurschied
the belief ofthe authors
is acre prominent than the beat
frequency (unless special aiacriaminating method is used),
8e that the successful results obtaind by Matsuo might be
due to standing wave rather than beat frequency effect.
b. Method use4
An altram-high frequenay oaciliator Qf 600
mega-cyeles
1t was
(wave-leagth a 60 an.) has ben used.
frequency Modulated to
, 0,19X108 ecles
cycles/see. (two separate experiments).
/se.
ad to1x108
The beat frquencies
after being rectified by the detector were convertoo into
nieronres. Both the oseiliator ana receiver were of the
Bo.. type.
e. Exp rimental Results obtained.
See-references 14 and 10f also fig.
4 ana S.
29
do Mvatass
?bw An icet~Io
limear*
Th4v
&uthors bf ..
4I,*'v.Lpastut vU
ftoe a
tb. tupstal
of altituto to *matcvs w4
U3^1 this pawTU~..4W~
liao or
pave LUG way tV.wa4 tbo tt&uV* OctIta
Utor dismusim
tbhoiry ao.4
Is thi s~e ol&
furthe
JLI
Law.tUat4sa
Ot
fowA %M44
30
PNLIMINAR DESIG
(a)
AND EXPERIMEnTS
Development of the Tebory.
It
ts a fact that during the perioA of the
praliminary design, the authors have neither seen the
experinental results published by Natso as in references
14 and 15 aor the idea pateated by Espmasohied as in
reference 16.
from the suggestions of Prof. Bowles,
a basic
theory for the design of a frequency modulation type radio
altimeter was established.
It
is very much the same as the
one mentioned and used by Matsu
enly more detailed di.-
cussioms have been cared out.
(b)
General Principle.
The systen used oasiste of a trasaitter
and
a reeiver earried in an airplane. The frequwcy of the
transmitter is allowed to vary linearly fro* tine to time
within a few percentage of the carrier. This can be
illustrated by means of Fig. 2(a) and Fig. 2(b).
At any instant ta, the frequeney of the direct
wave is at fa while the reflected vave arriving at the
receiver is of the frequency f#, sine it was radiated
4t seconds ago.
31
Reace a beat fre ueney of Af da
to the direct
and reflected waves can be detected in2 the receiver.
Since At O(Sh,
and
it
af a t for linear frequency modulatioa,
is evident, that A ft(2h.
Therefore, the beat frequency ef can be &ade to
show a direct ana linear inuication of the altitude, h.
32
(c) Discusaien.
The system is
Let the
shown diagram atically in Pig. Sa
ecastrical path taxen by the radio %*90s be
as shown in Fig. Yb and distances are measured in =eters.
In Fig. Jb,
let
fm a mean frequency of the transuAtter.
33
ta a lalaum frequeacy of the transmitter.
fb a maximum freguaeey of the transmitter.
f =
overall frequency eabane of the
4f-fa
oscillator.
4
,
fa , and fa are instantaneous freqeaew1es
correspfndir4 to the instances t.
a
& t 1 and tareapsetively.
= slope of the frequeay-time curve a ±df/dt
-!Ay/r/
),
wher.
T
a period of the modulation frequenay In see.
let
a
* the velocity of light.
At the instant t,
of frequency f,
,
,
the tranamitter radiates a wabe
toward the groand and is
to the reeeiver after trvelLing the path S
interval of (ta
Whenee,
refleeted back
in a time
t* ) seoads.
-.
/a se0...................
At the instant ta , i.e. whe
(1)
the reflected wave
arrives at the receiver, the direet wave reaehee the rece-
Iver Is at a frequency ta corresponding- to the
teat
ts on the curve.
EvIdently
to - tia D/a
seeW................
By deteeting two waves of different frequencies,
at fe an
another at fa , a beat frequency current of
(E)
one
3,1
lqp(fh.
f.) cycles/second wili present in the receiver. At
a certain altitude h, both 2H and D are fixed, so that the
constant beat frequency can be utilized as an indication
of the altitude.
In order to express the beat frequency /$ as a mathenatical function of altitude h, a time funtion for the
oscillator fruquency must first be derived. Any attempt
to write the general expression of the frequency-time functioS
as shown in Fig.5b will arrive at a complicate expression
35
la
terus of Fourier$* series.
be Oiaplified if
Rowever,
the expressia can
we limit the discussion to a tie
intervl
of T/I seoends and the time axis is chosen as shown ia Fig. 4.
(3)
Beret
f = f,, + at ..................
where,
a = slope of the curve a df/dt
(f4 -fa)/(T/2)
= (a)/(T/2)
We can write
and
f
f.
- f
Hence,
-a(t,
+ at.
- f,
t.)
- a(t-(t.
t.)
*a(t lo t.-
(te*
From equations (1)
and (E),
63- a
-
If
f,+ uta,
f)
[((Da)
- ta)
l
(D/a)
(a/a)[tii -DJ
..............
(4)
*..........S
2H>> D,
SH - D a all iah
Therefore, ,/
=
(ft/a)h
From equation (4),, we
flihietly
(5)
............................
aa see that the beat frequency,/I
proportional to the altitude h, only wheata. The path taken by the reflected wave, 2E, in such
longer than the distance between the transmitter and receiver,D.
b. The slope of the frequency-time curve, a,
The first
is coastant.
condition can be fulfilled easily In ordinary
36
ait1tU
measurement.
For a distanc
betwes
the te'aminitter
eM teeoiver of half a meter, an altitude greater thea
Amters WIll eata
the reqatse
nSeMistea, a lineer
t.
to fultiul the soomt
edatia
ret
system an
aretri"
be ave14e.
It Is obvies that the same beat frequenm
btainst at ether altitudes too rer4les
the spe Ot the freqOemqy4ie
wil
*erve since the beat freeztns
from time Inteeval of 1/21 setSMa
time Iaterval exeept at polats Ike a, b ad
where the rate of frequeny variatioa is
eo,
at lnstanees t a
be
at the atga St
queasy has Ae aegative sense. Ibis autematieall
the diseasi
astable
ttg
ems latrAeso that say undesirabIe lastataneoma
haMe s
J
"b t
t
to eas
in FIg. Me
equal to Sere.
b there
ns so beat
fretuae*y ia the deteeter.
Prem the above disssicas
the fellowing theoretteal
erves (Yig. ga a" 8b) ar dsam.
Pt. the above diaeussions, a frequeny sedalatioa
smas4.
type radio altiseter may coasist of the following e
a. A very stable asillater of any easwomet
frOMeeay.
b. A resolver Ot high seasitivlty but of breO"
t*ity ssee
earrier.
slest
the trequency deviates a few per Oesat free the
37
c.
A frequency modulating system giving a linear
rate of change of frequency havbng a charackeristic as
shown in Fig. 3b.
d. An efficient directive reflector for the transmittor.
0. A frequency meter independent of ampIitud*.
A linear frequency-current chaar .cberistic of the
frequency meter is
preferabie,
because the aititude is
directly proportional to tie frequency.
38
The
fransaitters (referenees 18, 19, 20, 21, and 2.)
(a)
Selection of Frequency.
Froa the consideration that convienent reflester
design of hisb directivity can only be easily accomplished
with transmitter of ultra-high freqeney, an oseiiLator
of approximatu ly 300 megyeles/second
has been seleet.
(1 meter wave leagth)
A very stable frequency ebaracteristie
was achiefed through the use of a successfUl design by
Mr.
A. Peters*& of N. I.
(b)
T.
Selection of the Oseillator Tubes
Due to its
ruggedness,
whieh is
particularly
suitable for field tests, the R. C.*A. 9b5
(acorm tube)
was used. The maoluum eatput at 500 megaoyelea/sec.
loe
is
than 1/2 watts.
(a) Design at the Tank Circuit.
The esillator cireuit is of the tmed plate type
as shan in Fig. 6. The overall tank capacity Is 45
aM the overall tnak indesteace,
6.21 wa.
details are illustrated in Fig. *
For go0
iand,
The design
a and b, and Fig.
.
agacycles/secad,
LC a 1/S
= a2
x 10"01
Assbing a total capacity of 45 vafds, the eerresp.
ending inductance is
6.25 emw.
Por an inductance of 39 oter tube and 1a inner
39
tube, this means a length
of
X
a
L/ExlA(b/a)
-6.25/(2z1.1)
Long or 1.1199
ne.
- 2.64
or 1.25' approximately.
This gives a revised figure for
L
of 6.3 eea. and
C of 44.6
a
corresponding
afds. Therefore, 46Safds
is sufficiently accurate.
For tube loadings
C'f + Cf + 2C1
6 ufds
The effect of inductance of loads will approximately double
this or 12
aufts. Stray effects such as capacity of comeeting
leads, etc. will introduce further shunt capacity so that
it can be assumed a total capacity effect of 20 uufds. Reace,
we have to design a tank capacity of about 21 uufds. Assuming
the end plate introduces about 3 umfds, the concentric
condenser is then tc have about 22vuufds.
C a 51 /9xln(b/a)
or
ln(b/a) =
xlC/9C
For a length of 4 cem.,
ln(b/a) = 20/198 = 0.101 or &/a
If
a a 3',
b
-
5.518'
=
1.106
Ui
onAm
r
~
I--
ay~
WWAX
42
Wet
b - a(*/1#)# - S~alaa
1610 sezx0(b/a)/i - (
UbM
- .
o.Os m
e...
er 1.s
or 3(9/18)'
From the previous desiga, the oscillator frequemey
without modulation system was experimentally fomnd to b
28
msga-cycles/se.e or about 1.0 meterk 4W wave length.
The ezprimental determination was done by beating the
scillater wave with the 14th baraaic of a knoaa stable
eseIllator built by Mr. Peterson I& General Radio Co.
The maxim= laput used was
V a M
Iaput
volts
I ,.
watts
The maximm output was estimated to be less than
1/2
att.
v
The
(roefreanes Uz,
.
Two types of receiver were used throughout the experisents.
To design a receiver for this type of work,
several requiremeats are esseantials
1.
light weight
8.
smal energy consuuption
B'.
high sensitivity
4.
broad selectivity
I.
miniam
condenser resetting
13
At first a self-quenched super regenerative receiving
device was built because of its extreme sensitivity and
broad tuning especially fcr ultra-high-frequeney receptions.
The circuit diagram given in Fig. 9 shows the arrangeaent
of the elements.
One stage audio amplifier using tube 41 gives sufficient
44
volm* to *p*rate a pair of earwheaes.
44 Oaw was ttea
asure only Gt*$t
The whole usit
so tkait the le
la the radic frequency circuit were redeed
legth
Olw~mer pOSsiel.. By
to minimu
aing a half wave
aluslams
tubei aatesa without retsWter re..ptioa was quite gloar
of the
hawred yards with tha plate sauppl
p to thre*
directly frme the Ij
t=mitter 0oeSte
seatse.
the baekgreomt .ois. became pre.dsaa.
Beymd this ram*
After sowe 3ang taste the
athers fvumd this type
of receiver *ot suitable for their purpose.
*hafge of resistor As shifts tming
that a resetting
a.
to sush
A slight
an extest
of the esa ser is assaqry.
queChing frqueoy
The self-
detector is 4uite ustable.
*tta
the q6enehing freqUency stopped ed the roeeiver became
umapeepsive.
The
The flant
heating
is very
rtua2 too.
hracteristio hissing Smase of sOPerregserative
reediVer wiUl be h6ssing iftbe filwest voltage is
uderwated
With freqeey
meaiti
ap to aromd three
the sigal is almost dut off.
-ega-eyelos,
Wah 1s not bres eseUg
Mdeal respsse
wea
sestiity withia
This
a
for the preaset purpos.
4 he a
-aost
th
eharacteristie ae).
ba4d Width of thirty to forty OW.a
cyees. "a. to the streag bekg4una
noise of a swper.
regULerati receivers a higher input signal is nessary
to $1ook it
eat.
With all these deficiencics in minu, the auLiors
went on to try another staplei.; gri
dttector as snown in
fig. 10.
This simple
1551
receiving device
w4s found very
-
satisfactory except that it
re
sufficiently
:not
sensitive.
r
r,
was
A high
amplifier was
.gain
ncessary after
the de tec tor.
The sonetimes
picked up stray field interf*.rerice if not
Rowever,
rell shielded.
this disadvantage can be cffset by increasing the
signal stregth ofthe trans4oer to reauce the necessary
aiplification in the receiver.
The antenna weas tuned to a half wave length, &nd the
antenna coupled inductance coil is only an extension of
the antenna rod about oae inch long.
Becausc of the ultra-
high-frequency carrier used, C&, C& and Cs are only strip
brass connection leads bypassed to grouna through aica.
The whole detector including the acorn tube weighs only
46
several omees and *coupies a space of three sauare inhe*.
Shield wires were employed in the input leads to the amplifier se as to minimize the stray field pick up.
The
frequency discrimination within a maximum band width of
9 megamycles, was mnoticeable.
Th
freassans Mters
(reforence 26.)
The frequency meter used throvghout the experiments
was based an a circuit f irst
with slight modifications.
mployed by Dr. F. V. hut
Fig. 11.
This frequency meter has the advantage over similar
devices of other types in that the frequency inAcatias
are iadepeadent of the asplitude and wave form of the
impressed signal.
the diretc
It increases the ease of calibration by
reaalng scale ca a standard alerosUmeter.
is capable of respanding to rapid variations in
frequency of the applied signal.
It
the
Assuming that thyrtres R
is aon-conducting at the time, and that thyratroa A carries
its
normal plate current, the condenser C5
tube A, an
ci-adenser C each becomes charg ed to a voltage
Er equal to the drop across
affected.
associated with
A while the other CK is
us
When an input signal is applied to the transformaer
Ta , as soon as the grid of tube D. becomes sufficiently
positive, a& are discharge in B will be initiated and the
potential of the eathode of B. will be raised abruptly
to a value Er.
Since the voltage across C is
unable to
17
48
tarily be carrIed positive with respeet to its aade
vltage equal to -y
drop
lek s the tub
eOes A#
I& A will be eza1
, the wr
a
b
Simes
ti"e negative with re
the grM of habe A is at Whe sam
apewt to the *athe
semom
eatheod of tube A will
,a sbarge insttamsealy, th
islhbO4.
2*a sImilar fashtes, ainea the voltages erosea Cu *gsmet
*bane instaItanses7Y,
will be raised maestaril
eurreat psi.. will
isbhage
to a positive VOLtage a ad
C, the ster aa In".&
fil seale readings for different ranges of frqueasiesw
mm " he .armt
Ster 49Opemd wpm
It
a
through the sieoraaMnter
My Usitg differst values of Cu ad
*ate
ouulem41od
et the
beth aued
1Mpulses disharging throughb.sh
"1s voltage asaanes
beeoiag Oharget4
is essetial that the plate voltage sheaUd be kept 640-
statie.
Itweer,
three welts 4o"
The filaset
it
was ft
that a deviaties of twe or
not affect the "scuraq
supply may beobtaae4
&eWies.
is
t
from a M
volt AC.
trasformer or & volts D.C. without any appreciable 4iffer-
Figs. 12, 16 and 14 are typical characteristic ourwes
of this direet reading tfretuey
at full seale iniestions.
mster for different range
At 2000 c.p..
that the devise faled t* work.
it
was f4und
This was due to
he fast
that at suih high frequeacis the tubes can not 4eienis
eoapletely at seh eyele.
EMMEM
MM
Ig74
Moll7
M7I
gi
44g
i5i1ii
7!li
Liggg
i~~~
t
gigigti
gi7a0gie
+
Er,1I
Kt77-
--
ILI :-f-
i.nj. 4
L
-7-7L
7---
tT
7-
t
it
.. ...
. .
;
M+
-Lt
-
;
g
-11
-4t17-
7
-7
77.1
A
7i
L
t:
. . . .. . . .. ..
:A.
7
v
jr IL
77
.
52
Because of the high impedance grid circuit of the
thyratrons, it is necessary to work this device from the
plate cirenit of an amplifier.
An amplitude variation from
6 to 100 volts input did nit affect the acouracy of this
instrument.
Ocoaionally the frequency meter broke into oscillations.
It
may be due to one of the several causes.
First
and most probably that the triasformer say be resonaat with
the plate circuit of the amplifier.
A distinct hissing
sound could be heard within the transformer.
Second, it
might be the radio frequency induced in the circuit.
The
requency
odulatie
The frequency modulation system consists of a
otor
runaing at cens tant speed to vary periodioally the capacity
of a condenser which is connected electrically in parallel
to the tank circuit of the oscillator.
The system used
is descrited in fig. 15 and 17.
From Equation "
/3
where
(3
(E2/a)h
- heat frequency in cycles/sec.
i a altitude in meters
a
and
m-
where
F
and
velocity of light
x
8 m./see.
08
F/(T/2) a rate of frequency variation
ft, - fa - maximum of frequency variation
T/2 a time in
sec. during which the
frequenCy changes from min. to max.
For an exptrizentaI. ranget a posbible variaticna of
a~ltitiad viI.
be from 2.5 to 60 seters.
beat frequ~ency capabiL
The atcsirable
of bel~itU a"Ie
b~y Qrii~ry, audiio.
f requeney transf critrs an~a th . (,-Irsct re
ii
x.Aers wouald ;.e from k0 to 5OCC cyc~cs/s*c.
%.. e, th~e value of (S$/h or
/as8o10
therefore
a-=(8-IOC)AE a
..
,........(8)
fre!.. ut .cy
54
Fes
4b, whon'the aotor sakes one revoluties,
U15.
the frequency variation will take two etplete
cycles, i.e.
from the minim. frequency to the maxim and back to the
mininm twice.
senwe,
1/rp.a. of motor i ST
or r.p..
of ator
=
1/2T
therefore, r.p.m. of motor a 60/2T * &O/T
Lot
£ a 1/2 a nodulatioa frequoy
then,
N a ropo ./.
Synchronous ators of both 1800 r.p.m. and 360t r.p.a.
had been found available in the laboratory.
For r.po.
a 1800
T a 30/100 a 1/60 &*a.
Since by equatica (#)
a M (4 to S*)a
and also
a a F/(/)
therefore
AF/(T/ )
0
(4 to bO)a
and
A ? a (4 -50)(/12O)a.
Rene*
A F M (4--O)SZ5z10/1t0 Cyelea/seo.
a (10.125) aegaycles/seo.
For a mean frequency of the oscillator to, of approdaately
00 Sesa-eyeles/seo.
variation of
It
corresponds to a frequency
.3 to 40%.
#A consideratica of the space available, the smallast
pceta.ge of frequency nodulation of a.i% was chosem.
hcal Al,,*t",--I,-,--
01
J-OA4*
-7
42
cy-d
A,
-7 .
.........
q
40
17
.77
- ZL---
1:7 7-
p
q
1,04
:v
001
7 77 --.
V,
71
7-.
7'-:,
Ac
F7
bi
7
q
56
This reaalted In a design of&
1.
A/h a S, or / = ft
A f
t..
S.
10 Segacycles
motor speed a 1800 r.p.m.,
ot 5600 r.p.a.
The design of the variable condenser will requiret
1. A linear frequency variatica characteristic.
2. A maxinam frequency variation of 10 megacycles.
can be seen that tte total capacity,
In fig. 17, it
a Ca + C1 , and the totAl Inauetance,
C1 + C
gB,
S- 6.Ueen.
sine,
r i 1/WU
a 1/204L(C0 +C1 )
Ihemfore, the mximn freqtueny,
1/24%c whlon Cx a 0.
t
From physics we know,
Cx a A/4d
am..
The area of the *uadeaser A varies when one of the plates
is
rotating.
Let us limit the discussion from t
Then,
A a (1/2)D/4 0
where
aat
and
of(S/60
cn,
bad./sec.
Substituting the value of .,
A -
wheare
O/8
k -(DI*/
(Se/S)[l-
a kt.
(*/***S.-...............0
=
0 to t
=
T/2.
58
By
Oqu.t~ce 7o
C
-A/4"4 *a
t
~r0w~~k44~
Let
"Sy or
Gx-ayof cc*
i
IY)AY
USfe
wha
smLl perematage yp saY less than 10%w
ftr a
By binomial Owpasioas
Y)
fb(lm
pance* the frequency Variation is linear whon a
wall preintag
.kkamo of capacitY is vzod4.
at
amd at
&? r
t a oi
tb
%a 1/2 , f~
tf&
3xI*G Oyeles/8660
1 /60 seet.
Ca
C 0+ C1,
Con 46
to
Cam a =to. approxitately.
therefore,
fb
C. & to z 1-2i
(I-~
)
59
gem* we am determine x fre
equaties (11).
lrb (11),
(T?/Cg) * 44y/f
- 4(4/fb)
(40/S)%
- 4(/a
tbrefore,
x 60 x 50 x 10* m
S.Lla
xo10*"
"
k/d
and,
k/4 a(16
)a
(Do/8
trefors for
600 rey
1
z9
=Ox
x
x"9.
WIG*
U/60)x -- *
D.
(]D*/d) - 198 e9.
Aesga 4 - 1/6 Inch a 0.16
ation,
cm from space considr.
thesn
or,
D a 6.5 ca. a
1*1
inches.
From a space censiaeratica, the diameter of the
plat
=as ehosen as 2 inches.
This gives a slightly
smaUerr4 of less than 10 megmaeyC/see.
I ftg. 22, frem experiental result, it
is fasnd to be
9 OMgacyOls/me. which eChets with theiretic&
predictlem
very closely.
Ia order to have the frequeney variation linear, It
Is meatinod that the valve of y must be saler than 10.
y a CS/CC by
efiAition.
60
max* y at mux./Co a x
*)
From (g),
thwtot*,
rmAK*
This to =*Ulle
%"a
2406
l~wefcrs
U1ar~ twequW~ vawltia.
I*
ag d4.1~
ad
twqulwao "
0
60 em Oipeet a
2bis isch
d
Q*t~
85. law a"YoottLOI variIGor
Inau
ukd "is Pwobb
*Uaa
rt~a
bo
/
4/O-
Oh xPerimsUa
O the
rsults la ft**
a". to the oomticj
betLyou tf
aft . &Ohk inviah "t
From wet e:.ae S? a eyllmdrloil parabolic
to sbo~a In 16' I&*ws "444404
11 (4f)
%ftao(
uiire
&ftlv, of rt.1
Ober*
5.4
wave "muth ofUma
,
.tv
Sw.r~l,
Ih"'LaSu
I~th *f the Pu*abr4ic
*
e
refloew
$Iae In our tosI~a Umi amaUet MlIA otwecL
ail*~
(f
to "0iwabae, the lar&eSt &V4aLeI
loia asSets vr* *boa& 2he piabillc
f sboa&*
ous~a
is umme
pI~tte4 SOOuL4in
to the M~thad .eatce
In
drawing ato etm
tvea1 J.itA
te
is .s
flu e.a A4v* Ion th at L41 a,*
A a
a*
is knowu.
Im &4calI
to"I 3*mth
-4 -
oAe
-El
6.2
The matoau* for both& io.
*or,
tt
ttOi
o si&-u4 so
£±ai
Of (.L/
ay7 dG~ft
1
rec-sor lve
i.1n4th
jA± (1u)A
.ro
trAl
wit"&
or bb tU
sup wo CAU tuneLi t,4
wtewoad tL ary
aby
atesirable oree)~e
'rbs original. theory L4LpaM ta* %&Us wow'
tt
Lhti.1
%"% U"s
a
b"" of~
X*U
ift ibs)*
can airpLmw abevo vqwAm w4A
from taw reatt
twqwwy of the 41re.t *mt*C!twUA
a4Lo mw,&
post the ph&a*. "Opaqet
Uoetad
fllowlft
to
lbs vktbi-?*ao obtaIa.
Um. &"&e too
frs~a tU. tIWA~ Uto on.
ehi.. Aftaer aweral &"ifIsatc
*L
~a'~
ea
O thwwaaattr
easbelo
Is.e
116t
#IC
vVAw
mw th
*a*a of
UI"Aam
-"0
stsa aw
#~qa~
te a& m*61Avttam
4
I* ftawiags w~4 ehat for rctata
16 14 !Pattw
~
Ot Mo aeem"ss
the Most ptedkhsL~t Otas. tSMt .t%u"I
Obeiut* OaUt~
&"a""
*&a Umu
ww~v wwoa
b.Ul*
ara
to ASO
awq
havS
ANSAamai
desu%
at
&&&twuksss
63
go Mhe
effe
of alstor field ca transaitte
ibration of taxasilttia" antena.
4.
was devoted to correcting Uewe
The first ptrt of this wer
faultaa
At the begianing the rotating c.adezser was seumd
a
ws
whie
sk
to a solit brassat
direetly to
n ete
The
the plate teak eirevit through the baJL bearingso
lta-higb-frequeoy curreat bas to pass from
taet that
the rotating plate to the tak
attae
Altheug
mdesirable.
t
makes the ball bearing
a buesh
sa fixeds so
nestims suffered the
aprovemnt was appareta
It
essattoa of eseillatica.
Probably the brush am ball
beariags formd a loop whiok stopped the transuitter froe
faaetiOatUg.
nte
net step udertaken was t.
ball bearings with a bakeUte oylade.
r.,laos..at of
This alternaton
aeosenvstabiUsod the eseillatica, but the revolvLag ot
the brass rod stiU reverberated the vhele oscUilator*
Thenceforth a two.4eek woodAen support was a&e.
te
tap
boavd was Isclated from the bottom mne by Puwber aushions
at each of four logs.
were on the the top.
The reflettor and the transwitter
(.e.
Appendix).
The power supply
ama the actor were en the lower dook. The rostiSg oeeno
Is elaped.
teasea
supported by a bakelite sthft/directly ma the
Setoq
The saft
is isolated fro& the Oseillatr W alr.
61
Thus the? Vibration pick up is
recuced Lo a minimun.
However
tle3. suACCC.s Lie alteratLons have decreased the maxiau
percentage of acaulation as shown on figs.
and
a
42.
The field tests may be divided into two parts, using
both tranuaitter and ractiver,,and using the transnitter
alone.
Fig. 19. illustrates the set up eiploying separate
transmitter and receiver.
They stood side by side and
the parabolic reflecttrs were oriente'u in such a direction
as to fUes
a lare
sheet metal object about twenty feet
away.
7Er
C/
dfe
65
A strg
60 eyele sinal was rgigstered by the frequeaey
mter.
By dis
motor still
waaneting the aeauiation Qsedse
running no signal could be det cted.
with the
This ld
one to suspect that the phenomenon was tne result of an
amplitude modulation brought forth by thi frequency mod,.
lation ad- only affected by the direct wave# aeverthelees
webft the ebect vas
oved slightly one eciuld notice the
change of wave shape of the oscillograph.
objeCt etirely
To nave the
the background noise became very disturbing
&ad made the sixty eyele signal juat audible.
This experiment gives one the belief that passe
displeeenet plays a very preac"imOnt part.
The signal
heard after removing the refleetlag object may bae been
due either to the aplitude mnanl tics or to the reflectiva
fto
other sw'rmding surfae.
In erder to ratify the belief that the phas. di$,.
placement of the diwet and relocted waves should dater..
aiN
he altitude only the transmitter was us4 and eoaeete4
La suk a way as to ast as a detector at the same time.
pig. 50 shows the circuit arrWgemnt.
fa 'IS. aa £put audio traafsemmeW.
IM0
r.p.m. synobe'noas sotor,a BM
Instead of the
r.p.m.
mse was tried.
hen the parabolie refleetor was direeted at the she A metaL,
tweuty feet aeY, a distuintie IMO Cycle sigal iatieated
itself as the frequaeay aoter.
his is due to the double
66
plate formation of the modulating condenser which double*
the r.p.m. of the woto.
Gradually increasing the distance
of the objeat from the tra.nsmitter dia not move the indicator,
although there was cyclical change of wave shape noticed
on the oscillograph screen.
As soca as the oaject reachea
a distance or about 60 feat, the 120 cycle note et uld act
be detected,
Increasing the aip.tfler gain, the background
noise, aad the motor field 60 cyc.L
meat bore
plak up made the experi-
ifficult.
froa the above field tests the authors were more tha
ever eavineed that the phase displacement of the direSt
and reflested waves to the most important faotr
in deter-
aiming the sboolute altitude of an airplane aboe a gead
by the freqenay sidulatin Athod.
pcsitire reult
Wafortunately
s
has betn obtained to etafira this asaeption.
Tis is fmIunamtally due to the laca of some vital features
in the primary "&sg,
as will be shoe.
from the resuIlts obtaind ia
following eomlusions may o
a.
desAae.
rees.s
the
drawas
The *zeriumetal resaat
to what woul
the experiments,
have
hewa faets negative
be expeted in the theory of the preliinaary
The faikare may bo du* to amy of the following
67
. Def eats la the tbery of the proa
tiary dessia
t. Defects in experimntal apparwatas.
b. Although the principal eperisestal attempt was aet
soesessful, results obtained for the aariwtary desigas
such as the oscillator, the
the refleotor, the
4rdulator,
antennae and the frequeney meter chete
witain reasonable
1imite with theoretical prediations.
was fouum that Instead
From exprm-eatal. resuLts, it
of the eQpected beat freg.ney as de eribed in the theory,
an altemaUtIng oarreat of twice the frequency of the noter
bad bees all the way Obserred at varios latenaities as
growd rfleterw
the atitietal
saa ouing eithee toward
er away tres the treamtter asd reeiTwr.
A elaser
aaiatic s
the ayant
will show that
mw ponte whieh affeat the result et the beat frequema
had bees neg1eeted ia the -pteries eensideraties,
a. The eteet of Laperfeot 11narity e
aalyi
the frequees
medskaties.
It
trequeay
has boon shOma frmo experimental remsi
modulatioa euvwe was weend
at the tops intead
Ot ta sSet triangular shapes, as Showa in fig.
From the interval t"
that the
a an4 b.
tA, the &pe of the freqwuey a
baek to the
varlatica e&Mages froe safat,
to se"
afeative slope.
tq% is appoximately 1$ of
The Interval
68
69Sb. total per Lod 1.
*fttA#t it
* tUAl at I***%at"
fwefaq a. shown I& r4.
A O~*S "Wa11e
tus
Zrqmay vatiLa
st SAW
iisaw cuoatwtt
horn a
io ato"tUMS
M.
St WO beat
bs
rathRAWIt4*4
W%a1J.LS bV &WaOLatJ
*uw* as F.turtov
ofi a"*. tgkwtms#a. *111 sIU at least
.Viitut* m~mIatics of tieque4w1*fro t.
owl*# la ttana
tb"esLslg &a
~i4tb
ftuiat* Swlt1v4.a of suwa trquasay 44 a WOOMLS or
mai &&q be cue or the expliaat4ias or aw
V.ILt athug
WVbbw the IntoSBi4 cm t"e Oeff*t AQt %"
&US"%Udse *4i&AUtIQ& *bZ.U1
be a Stwu~as the Qb'ber've
wq,,ll es %bethery 46~16"e
so n
o~v
Off t
ais pro&At
o seab. v* LrefaICOUNt
OwnS the tbatq waew be"
maw astlaet
aersWe
&ti de*4a taafo outp
twn" lb. 4romad Ow reflost" bb"s Ul *ill
6h&V~ beat
~7O
fw~queaq* Sc~
a of various amplltutes*
SMeb ecaposmt
mej have a stuengta s weak " to be bloae& out by other
do
Itfot due to the standing wave phqncaaa,
FlmaI14 0 & nost Uportitut point hAs beva fou
AUS"Oete4 in the theory or tha Pralimiar
the eyalie pha* e.ticzn betweaa the
tesigno aGAael
iia1tiog ank re.10lecto6
waves as the frequency of the cacillator is vaqsr4. This
effect will. be theWovgUl
pro* the laprowed tb*oa
bF th
Um*tiatd In the fisil desiga.o
4ewMIP.
Mter,
It is belieVe4
authors that the eaperial4roelts obtaized In
the plelIinl-ary ezper1maets carn he tborougbly *xplained4.
The de&Un uses In the preliminary ezermts
tbe Isproper, as mmr bo ses
In the follaim
Is considerod
Levelopasatso
j l,I
77r
-- T7
..
77
. ....
....
7
7
7:-
io.i
V
-7-7
xo
77-
i:A
a PRW
L7
7
7--
.
7
-7
i:
7: 7-
------ -7.
-----
Me-
------ -
f 7.:
AP7
J 'V
7t-'-:
7--
7 r--
7
I
a '.1
.7
_7
T
;7:
17
-
Illy
73
FINL DE8I1g
I. Gnral Prineiole
Weferring to the s
in Figs. I and WTa,
airplane
ill
length fro
current every hair wave
the reflecting
from
s explained
can be seen that a 4etetor on an
indicut a Sin
airplane changes,
cyclically
it
wave phosena
rfaco. As the altitude ,f
the
the detettor current will cne.age
azia a to
the caset when the altitde
inian.
Is held constant, while the
frequeny of the eeillator
by certain means. Due the
Bow, let as exaaine
is varied over A wide range
baage of the relative relation
betweea the altitude and the instuataneois wave length,
the earent in the deteoter wilA. also vary in au.ccrdne.
with the frequency variatio.
It
to a suffieiently large extent,
the frequency is
the detector eurrent
variation will be a peri4ie faaetion of
as shewn in Fig. SO.
varied
2he amplitud
be frequenoy
as well as the period
of the earrwnt variation in terms of the frequency anit,
will deed an the altitude at
bich the frequency vries.
Assumiag that the frequewy of the eseillater *au be
adated to suac
a value at whiek a MINI=a
=
teteeter plato
will be obtaned at a ceartain altitude. Let this frequency
be fiefa.e4.
airplane,
Them, without changing the altitude of the
the frequenoy of the oscillator is inareased until
another minimum detector current occurs. Let this frequmeny
be frof Fig.4. It
is apparent thatay
eheage
74
have sbortene
the wave lenth of the trassA.itted wave to such
an extaat that the sew wave will travel over the
when reevre
relatie
will have the same phas
ase path and
to its trans-
sitted wave as the original wave of frequency f, bar* to its
transmitted wave.
Referring t
frig, Z , the path travelled by the reflected
wave is Sh meters.
h ia moters WerrespdIng to f,
Let 21 be the wave La
kbe the wave lesgth 1a mters correspomdiag to frequeney fl 0
It is clear that for every 7j mters in the path
trevelled by the reflected wave,
the phase of the reflected
wave *hafte
me amplete cyle, i.e. 360
angle.
the uaber of cycle change for the wave having
Zen*
frequesoc
an
f,
is
the wAsber ot
f .isg
1
-
segr~es of electrical
-
-
(/)
clie change for the wave having frequeney
n
.3)
Since for both fr4-queacies, minian
detector currents
are obtalaed, the final phase relatAaa between the Qirect and
the reflected waves mast differ exactly
as*complete Cycle or
phase.
in..
~
,01
-
?-/
/ f
' 'ete.
From equations (I.), (a), and4 (i),
we obtainea the re-
.
75
lations
Rh (patting,
ft
=
where a
velocit
l =-,A,
"
t
a x 10 6/sec.
Lb (
we get
Let
9
h
f2
-
r
a *af
a frequency internal tor two sucessive
aairnim currents In the detector.
Ikea, we finalIy get the expression,
F
equation (15),
a certain Atitae
iaterval (4),
the oaelater.
it
is seem that correspouaing to
h, there is a certain necessary frequency
ma r,
4 1 4de
regardless of the ueVof the frequency of
In fact, Inste&u of two swcessive ainiim
curreats, either two sucessive aXimaM'tmurrents or any two
successive equal amplitude of detector currents will bear
the sae physical Meaning.
Further*are,
lower the altitme
it
is
h tw
see
from equation (lb),
the largerW
that the
necessary
(f)
The following is a table showing the x latioa between
sad
m the cer sspasuing A f,
airectly calculated rroa
76
equation (16):
PAW
Iai
j
? gnustiE
5
10
100
300
.
a
~
Fr equncy interval
meter
7 _mea-cyclessec.
0.
0
.
. . .
0
. .
.
0
. . .
. . . .
.
.....
30
15
O.5
byt.he above principle, a Airect inuication of the
altitude can be obtaine
as follows:
Refrring to fig. /S, through the turning of a motor,
the wavesi-of COntinUaly varying frequency are rautateu.
The reflecteu waves are ingressea upon the aetector.
The aaplituae of the resultant current at any instant
will,
of cwse,
depend upon the instantaneous phase rela-
tion existing at that time between the current resulting from
the airect wave and the reflected wave.
Since the phase re-
lation is continuously chaDging cyclically, the resultant current will underge a cyclic change of anplitude, thus produeing an alternating current of low frequency in the plate circuit of the detector.
If
the frequency of the transmitter is
varieQ by the
frequency modulator over a frequency range several times as
wide as the 'frequency
interval", A f, necessary for the de-
tector current to change its
aaplitude through one coaplete
cycle, during 1/4 revolution of the atscribea motor, several
cycles of current fluctuations will be obtainea in the plate
77
cireit of the aetector.
If
the periddic time rate of frequency variation is
made rapid by increasing the r.p.n. of the motor,
ber of current flyjctuations pr
of the detector will be proport
see,
the num-
in the plate circuit
Moreover,
wkly increased.
for a given r.p.m. of the motor, and a given frequency in
terval of the frequency modulator, an increase of altituae
will give an increased number of current fluctuations per
secdan.
T.se current flectuatias in the plate circuit of
the 4ateetor can be utilized as an altitude aaiIcator by
mseas of a frequency meter.
1I
Dise"sin of the
eory.
hrough a rough reading of the general principle in
this desiga, it
way seem to the reader that a airect ana
COgTINUOUS reading of the frequency meter
at each correspoMing altitude,
an be obtaine4
Put this will be shoim to
be erroneous )y the following diesussions.
Case 1.
Mea the altitude to be measured is a multiple in-
tegral of the mesa
Referring to fg
Lot 4p
4,3,
wave-length of the radio waves
.1
be the wave-lengths correspoaoing to fy, ta, and
f. respectively.
lot fb - fa be denoted by
riation of the mdulatr.
Fros .equatiM, (1,),
(A F), the
=maim
frequency va-
AL
T7
......
ir- i
7
4A.
"71
. .. ........
7
J:
7
T
9p,
.....
. .
-7
. .. ....
.. ...
_T::
-7
7-7
0
p w
77'
--
.... .. . ....
7
... ....
....... .
-------- --
7-.:-
4-
977--
77.:
-7
a
-7
-7 77-- :7-77- -7---T.-
fzi A.
77
7:
t
.
et
1,refle,-71
;; raCe-33,
-70L Call
f(OfIveNcy
r
we7er
79
we have
a
fit
.....
a
(16)
2h
where Ath
is
the necessary frequencyinterval correspod-
Iag to the altitude
direct wave an
h
for the phase difference between the
the reflected wave to be a complete cycle,
i.e.., M0e (so that the detector current goes fro& minim=
to azium
am back again to minimnm).
Benee,
a number of frequency intervals at altitude , h.
It
is
seen that
queany madulater aYsta.
dcesiga).
(AF)
is constant for a fixed fro-
(sek "s 10 mega-cycles in
heever, as the altitude,
h,
varies,
vary aceerd~lg to equation (14) so that
and is
zh is
(Af)h wll
will be varylng
therefore a fuanction of the altitude,
Case Ia.
relimiary
h.
an integer.
Referting to fig. 4-.
A the instant to, the oscillator frequeay is at
fa. As the frequncy varies from fa to fb, in the time
( or in general, Rh) cycles of ourrent flueinterval --I-,
tuatim are obtained as shown in the diagram in fig..21't).
his gives a frequesy of
Let e
them
denote this freqncy,
e
xi (h)
xh/(j)
cycle/sec.
80
N, the modulation fre-
has been denoted by
In fig./7(c) ,(T)
quency of the system,
therefore,
=
a
-
for exsaple,
o(
,
in fige 2
-
------
----
at r.p.m. of 1800, ane
=.
"60
J3
(17)
of a, as shown
.340
se
Evidently, when the altitude is 1/3 h,
them,
5
-a 120 ecles/sec.
Therefore, Under these particular commitions, namely
1.
the altitude is an integral
2.
zh
3.
The minimum frequency,
ultiple of
%,
is an integral number
as corresponds to a mini-
ama current in the detector at the altitude, h. Egr'm-P (/7)
The altitude reading in fig.24WJcan be plotted.
to fig. .2f again, it
is
frequency of the oscillator c
minimm
in the detector,
mum value,
seen that when the
0respon
Il, which is othe4r than the maximum or mini-
then the resultant frequency
& will not be at-
fected, as shown in the diagram of fig. J4.
Cast lb.
teah
s to a current
y al/d/kd c4rt/P
is a6t an integral number
Let us assume that
%h a X1 h + yk
where xth is always an integral number while
y
is a frac-
tiosal ammber greater than zero but smaller than unity.
-7
-7:
-7-
7.'
t
77
. . . .. .
7'
7
7 - 7
7.
*'-t Z""-.TK
J-)z
77
a
77
q
q
w.
81
L
q
7
TI
It
d'.
7-
. .. ...
-- T-1 7
7-'
77
:A
77
p
L
82
A diagranatical Investigation has been carried out in
fig. .25' , folowing a process similar to Case
For the case when
be seen
fr
fig.l
that
a.
is smaller than unity, it
as
,if
4 5/4
an
can
2,
if
xk.a3/4.
Hence,
from the discussions in
Case 1b, ge can draw the
theoretical characteristic eurves of the altimeter when the
altitude is
an integral maltiple of the mean wave-lungtth, as
shown 1a'fig..2.
Case 3.
Uaea the altitude to be measured is not a multiple
integral of the mean wave-length.
In order to get a conclusion,
let us first examine
the change of detector plate current due to phase shift of
the reflected wave a_a cometnt wave- l.Inth.
Referring to fig..27,
due to the stawing wave phe-
nimena as explained in the review oftio
is seen that for every 1/2
altimeters, it
Q.istaVce (distance between
suceessive modes) from the reflecting surface, the detector
wili give a plate current variation from
am
and back to minim
In fig.27(4)v
where
k
let
minium
to maxi-
again.
h - k (
+
is always an integer and 1 is
---
a longth greater
than sero but smaller tn(1/O)A,,
It is evident from fig .24)that the detector current is a
4
Lt
Il~ITi
II
T_
T_
t
--
e7x
b
84
k.
rmtlSS at "L ratbew thea
bo bnt Toryin
a emstmat altme
ftem Oquatum (),at
frequeny
a
Slslrlg wehew
f.
1~,.54),~eora~m109 to
f, A f, rea.
ll..41. ehhm be dorlma4 " the *bn* of
Lot
reasal
at f
bmk.)
altitu.
4w
to te
a"54W soonal pezmmtege of
to
tb
miim
f
varlattoa.
rema
umeulatiout
'Is. appr
Miatsu*.
L and (tofu);
wet
%wPeramteat of 31ilat1
It to *leaw from te
-P
a -A9-1 weve affect "at car-
roepoodIMt to every 4.fimlte uave-1"Uat
there is a aeeau.
77
m=
= ======
.
===
6r
.
4&
"NA
86
1
sary z
fro=
in order that the detector current can be chasged
aIt== to iniaina agaia.
Ibis is
aalegous to the phe-omea
iag to every deflaite altitma&,
there is
that corresponda necessary frequency
interval,4t, in oruer that the detecter current can be
changed for a cycle.
fte necessary frequency interval was fousa by
=
Af
fte
I& equation (14)
nk
necessary residual altitude interval, A 2, is
dently equal to
from fig.
e-fore,
27(4.
-
---
From this analogy, it
is
evi-
(20)
-----------
evident that we can repeat the
foregoing discussioss of Case 1,
in a similar way by sub-
stituting
6L
forAF,
aj
forAf
50, for
ana
where
h
A
.&
kp (analogo
to-
Therefore, withott repeating the same process, we can write j
1.
@/
2.
S/M
Y, and is
a
2=5
[r
if
.
defined a4
Yis
if)=
an integer.
1/2 where
is
analogous to
(21)
87
always an integer while
heis
I
7a-
a
bar greater than aore and smaller than unity.
S.
a/M
=[21-
al
<
whe
1/a
*eace a sallar characteristic carve for the frequeoF-altimeter ean be pltte
Amm
against
as shown Ia fig..2(.
t of the DisCussios
Se altiaeter reading is
a fametion of the two para-
aeters, anely,
1.
which Is
the ratio betweea4F
aadzf.
Its
value depends on the relation between saxima frequency variation of the
ater
axw the value
a
at various alti-
tudes.
, which is the ratio between AL ana62L.
2.
to
It is
kp, the value of which depenas on both the altituce
and the pereestage of frequency modulation
III IsetMMA
f
the Parameters
and 4 F, two
In order tesalect proper values of
famios of curves mat be obtained, namely,
$,at
variousg' and (B) a/K against
A.
Se curves W/% against
or
fr
*(k
equation (20),
since
kP a 55
at various
h at various
from equation (1)
Sh - k (
h
(A) s/I against
)
X.
88
nheretore,
h -- r
'
.(
or
%
or
v1 --
---
------
--
It Is by definition of the residual altitude,. 1, thai
from equatioa (21), it is seen that when h 4
a
and
"
negative, too, but the frequecy, a,
w negative sense,
oa
be plett4,
It
5
?
is
(
should have
so that a spmetrical curve of,
as shown ia
(-),
against
h
fig..28 , according to equation (21).
seen from the carve that when
is
b
greater thM
, will be directly prpportiemal to h, am
From the enabination of equation (22) and fig..2G,
we can pUt the altieter
charateristic curve,
q/M against
lh t various percentage of frequency udulation, as shoma
in fig .
3. g
e'
against
h
at various
Fref equation (16), ,f
55nL
a
the expressing xs,. Af
-
we get
I
ao,
t(--)
let
q a 2 e-).
so that
h
"W parameter
is
qb----------------------------(25)
q
is analogous to
to be called the index of the altitude
p
in fig.
h.
f.
It
--TIT
4
a
.....
IIT -
.
-
77!
. . ..
.. . .
.. ..
T -- I
177
a
/,A
-
.;tA
74-7
-7
Vl WAI
i:
a
,,7 7*
ice
91
,herfore,
in
Leordase
with fig.02
&ad
equation (gU)
we oaa plet a similar mot of charaoteristle wrve at various
ni 8 .q.
.4.'a. .h..u in
Up to this pointo the reader might wonder if
two in-
mmalnstent frequeaies mght happen d"e to the two parameteo,
aamA t
.
Akhis is not true, bvecause %ad
lated with each
A
frequeo
A J.
t
are re-
er through the relatioa between pereentage
modulatioa and the maximum frequency varlatioa
fer a checkoa
the coasistency of
f1g.f,
Let us assme,
and a frequmey meWlatioa of
L oeter
10%
them,
p90.1
how**,
q a £AP/4a
From fig.4 it
is
and A Fp x Jn=80
*
ega eyCles/se.
0.8
sem that same theoretical altimter
readiag wIllhe obtained because the abeissa for the parameter
*
p, is in =its of b/N).
92
froa fig. .2f, it
is
seem that k# am ideal altieter of the
frequemcy modulation type, the shortest altitnue steps over
*hieh te
kr used.
frequeney meter will show the sae reading,
should
Uis requires largest possible value for both the
pereeatage of frequency modulation and the altitude inaex
*ever,
the largest
p
q.
to be used is limited by the assumy-
tia, that percentage of frequencynodulation is
so small that
the mesa frequeney .An magnitde should not differ very much
from the mxi
ana
the
=4
n frequencies.
2berefore,
p
is limited to 1% for practical oesign.
As soon as the value
of
q
p is fixed, the only way of raising
is to choose a
shortest possible wave length.
la fig
, the curve
'6A'
having a shortest, step of alti-
tade should be easidered as a practical characteristic for
the desiga at radio altimeter of this type.
A vala
of med*at1s
of q equals 0.4 and a - xim.= percentage
of 10% will give A
of 00 mega -cycLee
a seas frequeno0 at 000 &ega eyeles/sec.
lengbh of b0 es.
and
or a aesam wave
93
of the standag
A. ApliestloS
"eSult
exPlain the Oxpwiaiatal
wave theoryto
obtainea in the pwlimlaary
the wave
Ln tha preliminary desig,
was
And the maxi.am freqsandy variation
approxImatoly oe moter
in the first dsoign of the andlatios systea about T.b
Tberefore, we had
mega eyoles/aeo.
Uhieh
asters.
,old &iVe a trequeay of 60 qeces/3s.
fvom fig..2
at r.p.m.
at U00
fre
sore altitude to an altitude of 50
This was oeatly what was observed. UWfortunately,
beyond eve& SW maters of
s observattems had bees ud*
distam*e. Latet, the
otlatioe
system was ehaget to
frequay
due to motor abaft and the mima
rednse vibwatio
warlatlom was tha
.aly 0.5 mg%
seans a vl& 0f
*
O.1T
and 4
altimeter systes would give
up to
q0.0 0
and
p0 .086
cycles per so.
=
which
0.U0g. The changed
a frequeny of 60 eycles/sec.
40 meters.
3.Application of the standing wave theory tb
expLaIa the experimental results published by Matsuas
An
xaIaniaie on the uniform altitude sters
tUls ant certetn wild points is
by Matese (referesoe 14),
it
the gablished results
can be shown that the results
sam be better latwpretated by stading wave theory:
Yne Ae
1
1
F. t.
:I
.. i
7
-77-
4
7,
.V
pI
fit
or
or
--- 77
r
'
'7-'-
7-
-7- :7----
-7-7
7
JOIP
ot
"00,
96
In
trC
a. 3,
the data In experIment no.1 by Matsmo,
1a =g0 mega cycles
'd pa
/ see.
a& K a a a a
w ,
hence, p = 54/57Q a 0.06?
q = 27/a =0.253
The theoreteal altieter
by the use of
itg.2f a"d is
results In fig. p
reading Is tben Oiotted
compared with the gblished
* A remrkable agreesent Is ebtained.
Ia a similar way,
the. theoretial altlate
data In the seoase OxperimeAt
reading for the earIestal
Ob. comparison between the
by Hato Is caleulated .
theoretial and the expertiestal readigs shows gcd
agreemest too.
Fros the aboveeoapaisas,
it
seems possile
that Mr. MatOso heactually fcund a step featim readig
whichean nt
be explained by beat frequeey theory.
Fwthearore,by beat frequency theory,
the
magnitude of the beat frequaey at constant altitude
It
directly
;peUtioal
varItion . !herefore,
to the
eitfr
modulatica nor the saudz
iae rate of frequenwy
the perSate*
of frequ
frequency var&atioa has to be
large, because the same time rate of frequency varIation
esa be obtained at smaller maximm frequeacy variatica
but larger modulation frequenny. Yet, Mr.
Matsue mention ed
thet
Asuccessful altimeter readings can only be o0tainedjarge
ultra-high frequencies.
uod$Uon
percentage of frequency
These words een only be justified by standing wave theory.
Furthermore,
from fig.39f, the micro-ammeter
reading in the experimental data of both experiments shows
same total number of multiples of the modulation frequwy
at equal anaber of altitude steps.
This cannot be justified
by beat frequency theory,because the time rate of frequency
variation is not the same in the two experiments. However,
this is ju-tifiable by standing wave theory.
98
wtal. r*Pdt as well
oMliwI4 ties "he e
45~Us3Ias tho "8i4S
U&Af tv."iass
mo4uLat~on mvtbo,
elroasIto pab3Lnhe
ati""tei
&ttkas&WO twining
tUe
Iid thboaet~cal polats
I.fte
aSt a raud
at
vl**W m06 Ux'Ou*.tavac
It is ObION that tbe tweqq&cy SWM.
Utios n. iapltrao4U, rt wave rai1o &ltisetris noe sost pre-o
theOW7 4.4reoip
th samilnoav
&athiA tt.al# Is b£w&1~4
tab.themat gase .j~aatio
e.
wave o
aa"afwSeey
asthe .sjerinaal re-.
OUGe iS of 10% with J0wor
estpSt at emuiit.y 6 cotts Is r~c umdsd a" mltak1e
fee zpertalcotirmation of the staa"Ift wav* thtkhy
40
***~S
fte .zp~whseatl rtaimU
to be Uw**Seable by Wat-rttwU*U
is 0011eo
*iJ*aaIAS L&460 tcX uASkL1ftiS Of tOe
theory. MO. Osy
eAp~vuwtmsnew5wer, uo'4$n
It
Is *zPlA
Ma16",
ais
the iapropew 4*sla a tse
st'il Ani Ite
Obtaln.4 In the pw~lza*
to suaidu
wave
b*
q
1 uat what should bo 4aPOSt4 f ro&
In the krollaiaay *triawats,
see"lgtis
99
Tki. tzaaaalttor
fr~ia.ncy s.t.w
az~4 ~~arabQl1o 1,etl.ctQr.
A cioe~ u~ view of ~ tft54..
uitte.r aa~ U.qiancy moti4atow.
AD
The
grid d*teotor and the parabolic reflector.
The frequency aeter.
102
The superregenerative receiver
The grid detector
103
Transmitter and receiver stund side by side.
r
Transmitter and receiver(right) neper-
ated by the house to decrease the direct wave pick up.
104
TABLS
TeeAn
ANte
Input Frequmey
co
700
Gutpt
1
1
C = 0.Ola"f
1000
1600
200c,
C.
i00
so
50(k
5CO0
59
66
.0onmt
Rd= 7 ohms
westn Klewe-
anseter 0-200
~aaprs
4CO
5000
21
33
4k
81
7
4L0Q
66
4000)
62
4050
go"?
&o
6000
63
100
500
600
1c0c
1600
8
11
1S
8000
3000
6*
C - 0.003 uut
qm .000
3500
vuf
k a a obms
Westa KEWro-
aaaeter 0400
uaapores
3600
3700
00
5900
40(f00b
4200
4500
5000
6000
7000
Wo1I
8
VI
40
6
88
90
92
96
100
106
119
140
164
105
Freqieun
Meter (continued)
Input Frequena
C. P. 8.
C a 0.0
At
C
40006 at
34= W00 obas
esten Elmo.
amter 0.400f
o
4000
50
W50
3600
6700
oo800
5000
4200
4500
5000
45
4
48
48
50
s1.b
55
61
*agees6000
wl .3
Cow .009 auf
'e
0 Oka
estma Micro..
aamter 0-00
83
95
116
20000
1
100
8
160
41
U60
f00
180
400
460
500
usagres660
600
660
700
740
C a.0012 aut
.003 af
0
La ere-ammter 0-*t
eaaper.s
1;
7000
8000
10000
200
C
Output
UMp.
50
60
100
bh150
200
250
300
51
69
80
so
V5
130
150
14"
160
174
104
191
2.6
&
8.6
15
17.5
220
26.5
106)
fr~z~aM~a
Arbitrary iotation
Anle of Condewr
Frequemey
megacycles
0*
10
16
20
22
24
30
55
40
46
50
60
66
70
76
80
45
90
9b
100
too.$
MO.
271.
271.4
270.9
269.8
266.1
267.7
266.0
266.2
265.
26.6
262.7
262.9
263.5
264.7
265.
266.0
267.6
Rotation 4agle
of Cdoadser
Fregaqaey
megacycles
10
to
0
40
50
60
70
0
90
100
110
120
150
140
160
130
170
180
Ml2.12
259.26
259.548
259.424
269.520
269.520
259.620
269.576
259,552
259.440
269.576
259.588
259.216
259.204
219.160
259.144
269.152
259.160
269.212
Rotation Angle ?fiquency
of Condenser Megsecles
190*
20059.26
210
220
20
240
250
260
270
&
290
500
510
520
550
340
350
560
59.288
259.588
259.416
259.500
259.520
259.54
269.620
259.440
259.400
259.286
259.160
259.120
269.092
259.112
269.116
269.168
259.216
see
Co 0*0
S0000000000*
00**
00000wo'I-'t
4
1.
C. s. Draper of N. 1.
. -The
Sene Altiseter
For Airraft - Teehnical Notes, No. 611, 1. A. C. A.
2.
1.. A. 4yland
-
Tre Altiaters - Aation, pp.
122, 1928.
.
W. G. Broabaeber.-
Blind flsag
4.
. F. w.
Measureents of Altitude in
- Teebaloal
otes, No. 608o, . A. L A.
a1randorson - Height of Airplane
Above Ground by Radio Echo - Radio Engineering,
vol. 9, pp.34 or IeIeAMe Dee. 14, 1986.
E. F. 3. Alexamdersu
6.
and Meas for
Me
Indoatig Altitude frcs Aireraft
No.
U. S. Patent
5b6,615 ,lme9
3.
6.
-
F.
. Ao
aGara
. Radio ESho Altitude
Meter
Journal of Aeroaatieal Sciones, pp.
vol.i,
July 194.
. F.W. AlexaAnersOn -
7.
816,
etbod and Means fot
Determuning Altitude fro& Aircraft - U. S. Patent
g.
1,969,87 , Aug.
7, 193Ae
8.
F. F. W. Alexanders=a - U. 8.
9.0
Keith Honey - Radio Enginering handbook 1937
Patent No. 1,91,148.
Chapter on Absolute Altimeters.
10.
W. A. Pleree and C. W. Dodge - The Applieation of
A Radio Frequeney Oseillator to the Measurement of
the True Altitude of Aircraft - N. I.
T.
Thesis, 1987.
11.
F. G. Patterson - Radio Bobo Altiueter -
B. 8.
109
U. s.
12.
T.
Patent No.
2,022,517 , nov.
26,
155.
J. boerner - Aireraft Rd1o Altiseter
Patent No.
2,Obo,418
Pea.
,
. S.
19M8.
C. 9. Terry - Aireraft Altimeter - U. 8. Patet
13.
No.
14.
2,055,88
, Sept. 1936.
S a Katsuo - A Ieseareh of Direet
Mater for Pilot
I.
-
-eeding Depth-
N. g. Of Japea, Vol.
4, pp.
1164, Nov. 194.
S. Natsuo - A Researa
i.
of Dlrect Rea4ing Altimeter
for Aermaaatical Use by 1adie Wave 3eflootiea I.
16.
E. E. of Japes, vol.
56, pp. a0, Feb. Is".
L. Espeaschled - Rethod and
Altitude of Aircraft
esa.
for Mesacring
U. S. Patent No.
2,04a,071
and 2,04b,QT3 , June 136.
17.
F. Guawaaseelli an
Meter
*
I.
A. 3.
F. Vechioacei
, pp. 60 and 1W,
- frequecy
April ad
Asg.
1951.
Is*
T. t. lesa - £6aa1at lines in LadL
I. B. ,
19.
vol.
8, No. 7, pp. 1046-105,
Circuits
-
July 1454.
F. S. fTena - &ome Passbulitiea for Lee Less
Coils - Proc. af I.
R. E.
,
vol. 23, No. 9,
pp.1069-
1@75, Sopt. 195.
20.
C. I. fay me A. L. asatl - Vaeum Tubes for
Qeaoratnig Freealoes Above 100 legacyclee
Pros, et o. 1.
3. , Vol. 81, No. 3, pp. 199-412, Iar. '36.
3I
* .Rlj
~524
dAo
Lv. ftml
saw iny1Utw#tw A& go & Vo.
me Usw
10941.
TO&* 34, Nov 3, prop.I" 454 la
A., 10lter
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Communicationi Engia4etr4, No. 4, pp. 3b2, septo IF",
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Problems for 6.252
- Due Feb. 20, 1939
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1.
Write a brief report on the radio aspects of European
Communication, as presented in Colloquiums, Monday and
Tuesday.
2. Write a paper of about five pages on the followings
Analyze any radio communication facility, like a radio
telegraphs a facsimile telephone, or broadcasting system
into its essential components from a functional viewpoint, showing and explaining a block diagram of the
complete system, and discussing the frequency band width
requirements.
Preferably deal with specific cases on which you can
find data, and include all references.
February 10, 1939
W. M. Hall
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