VHF NAVIGATION SYSTEM
GENERAL
The VHF navigation system provides reception of the VHF omni-range
(VOR) or localizer (LOC) ground station signals. The VOR data is
supplied to flight director indicators to indicate bearing to the sele~;ted
ground station and deviation from a selected course to that station during
cross country flights. Localizer information is presented on the flight
direction indicators to provide lateral guidance on Instrument Landing
System approaches (ILS). The VOR/ILS signals are 'also used as inputs
to the autopilot and all weather landing system (AWLS).
AIRCRAFT INSTALLATION
System components, cabling, f>Ower requirements and equipment locations
are shown on the "Aircraft Installation•· drawing.
The components of
0:1e
sys tem az-c
.:l.:)
~ol!ows :
~ rt~C€-i\"f:!'
• Vi-iF ;\;J.v Antem~a (taU)
• Local:.2~r A:ltenna Swit~~
The Collins 5lR-o receivers are directly interchangable with no modification to aircraft wiring or operating procedure. The \'v1LCOX 9765 - 100
radio set control and the COLLINS 313N-2 are also directly interchangeable and may be used with either receiver.
VOL. VI
8-1
lllc I •.
; •
I R(Q
rREQ
S(L
st:L
IMHz
.-L--iiMHz
VHr OSC
Hr osc
Q4
05
J6 .~5-17.85MHz
4.6
5.1 OR 5.15MHZ
(5.151-tlz HO T US ED }
OR
4.
NO ,
2 ._.__...r-- -,
VOA/LOC
5YSHN
ltrT HAN
WARN lNG
otv lAltl~t~ Jt~:~t- · ..·- -·
AND A'OHRON SW
.........._(A\11.5_)
. ..
I·~
I
l£rr'~tArl~· ·~ ­
AUDIO TO
INTERPHON~
AV IONICS EQIIIPM£NT
RA ~J 41'fllift lilt- ~Jl.Hu!L..:.. ..:. u .l
•\ Ill
VOR/LOC
!> 'fST(>I
REC[IV(A UNIT
NSTALLATI
RECE IV ER
BLOCK
DIAG RAM
51X-4
------
J
SYSTEM OPERATION
System operation is controlled from the VHF / NAV portion of the control panel.
The power "ON-OFF" switch @ energizes the system. A volume control @
adjusts the level of the audio output to the interpbone system. Frequency selection is accomplished by setting the desired frequency into the frequency selection window @ . The whole megahertz (MHz) selection is controlled by the
left knob @ and the fractional MHz selection is controlled by the right knob
©.
The frequency range of the
systllm is 108. 00 to 117. 95
MHz in 50 KHz steps. However, due to aircraft wiring,
channel spacing of the 100
KHz is used. When a 50 KHz
channel is selected on the
control panel (108. 05, lOS. 25
etc. ) the receiver tunes to
the next lowest channel. A
frequency selection of 108. 60
MHz or 108 .65 MHz provides
an operating frequency of
108.60 MHz.
p I L 0 T
I
s
RECEIVER
AND
COPILOT'S
CONTROLS
(T 't10}
Mode of receiver operation, VOR or LOC, is determined by the selected frequency. VOR operatbn fs provided wben frequencies from l OS . 0 ~1Hz to ll2 ,0
MHz are se lected in ev en tenths (1 0&.0, l08.2, 108 .-t etc . ) or il~.o "-1Hz to li 7.!1
~!Hz all tenths.
Localize r operation is provid<>d w!'len f requenc1es rr or.1 ! Of> .1
:-.1Hz. to lil. :J i\IHz are selected !n odd tenths (lu>) . i, 106. 3, t!tc. I ·
\'OR OPr::RA TiO::\
ln \'OR operadon tht: beartn~ signal can be selec ted to drive po in:et·s on Beari:~;
Distance Hea<iu~;; Ind!c::ttors , BDHii and Horizontal Situation Indic:uors (HSIJ.
Swi:c!1 p:l.n(.ds on thl :}:tc \ · ~ o. :1d conilvt' .s i::s: :-!.l.r:tC'nt P:lne! s are u~l-d to ::e!ec:
iniorm:J.tion displayed on t!Jdr BDHi. .Systt::n ::\o . i information C:li) oe ;; el\ic;eu
for the :-io. l pointers @ and system i'io. ~ can be selected for the :-<o. 2 pcin~crs
@.
BDHI pushbutton selector panel at the navigator's station is used to select information displayed on the BDHI's at his station. The No . 2 po inters are used tO
display VOR information. Bearil1g information from system i\o. · l is displayed
on BDHI No. 1 @and bearing from system No. 2 system is displayed on BDHI
No. 2@.
A
VOL : VI
..
8-3
.··
P I L 0 T 'S
S
0 R
c0
TA
T I 0 N
p I L 0 T
I
s
-.
The bearing to the VOR station, relative to magnetic north, is indicated when
the pointer position is read di rectly from BDHI compass card
When the
pointer is read with r espect to the indicator top index @ , the indication is the
bearing of the VOR station relative to aircraft heading.
©.
I
1
P.OH I
N .....
v VR-1
,~o o r- 1
2
v ,-;A - 2 . _,,. - 2
SOM
I
'~.: .
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I
NA V
8- 4
G AT 0 R
..
I
s
eoH 1 ' s
&
s ELEc r oR
P A N E l
VOL. VI
The VOR signals can also be selected for use by the flight director systems. Two
navigation selector panels on the glare shield enable the pilot and copilot to select
VOR- ILS @ signals for their flight director systems. The pilot can select signals
from the No. l system :tnd the copilot from the No. 2 system.
To fly a VOR radial, the desired radio
course is selected on the HSI. The
course arrow @ of this indicator is
positioned to the desire d VOR course
by ~e COURSE SET knob @ . This
information is supplied to the VHF navigation receiver.
NAVIQATICH SELECTOR
r
00
COMPUTERS
t
0
r-V£RNA V
I
~0 1M
i~~~HijLtcr
:fl.
ASN-24 ASN-35
TAC-1 VCR ILS-1 NA v-orr
NAV
•0 1 R£?
0 0 0 0
The receiver compares "selected course"
from the HSI with signals from the VOR L--,;;
P ;;;;I-LO_,T_,'_S...,;;NA;;;;V_S_,E~L-:E:~
C T=CR
=="'"":p:":"A~
N':'E::"L---"
ground station to develop deviation in(cOPILOT'S I DEN T I CAl EXCEPT
formation. This information is displayed
USES TACAN-2 & VOR/I LS-2)
on the HSI deviation bar
T he deviation bar indicates that the aircraft is off course (bar left fly left, bar right fly
right). -:t:he "to-from " indicator @ shows that the aircraft .is on a radial toward
or away from the selected station. The alarm flag
is used to monitor :he VOR
s ignal for reliability . When the flag is in v iew the information being displayed is
unreliable and should not be used for navigation.
©.
©
H S I
/
\
VOL. VI
;-; - 5
SPECIFICATIONS
WILCOX 806 A
CHARACTERISTIC
~udio
outpllt
SPECIFICATION
100 milliwatts into an external 200or 500-olun resistive load for a amicrovolt input signal, 30 percent
modulated at 1, 000 Hz.
Audio response
Less than 6 db total variation from
350 to 2 , 500 Hz.
Audio distortion
Less than 7. 5 percent at normal
rated output.
All undesired respon.ses
At least 60 db doWil.
AGC
Receiver output will not vary more
than 2 db over the range of signal
input levels from 3 to 100, 000
microvolts.
Power input
27.5 volts, DC + 10 - 20 percent,
1. 0 - ampere maximum.
26 volts (:1: 5percent) AC, 380-420
Hz , 0. 2-ampere maximum .
Frequency r:tnge
108. 00 to 117 . 95 .MHZ.
Channels
200 channels with 50-KHz spacing
are provided. Limited to 100
channel lOO KHz spaci:1g.
8-6
Frequency selection
Accomplished by Mark 2 staneardized
navigation frequency selector
designed in accordance with ARINC
Specification No. 410.
Frequency stabilit';
Better than :1: o. 0035 percent 1111der
all operating conditions.
..
VOL. VI
SPECIFICATIONS (continued)
WILCOX 806 A
CHARACTERISTIC
SPECIFICATION
Input impedance
52-ohm coaxial.
Sensitivity
A maximum signal of 3. 0 microvol ts, modulated 30 percent at l, 000
Hz is required to achieve 6 db signal
plus noise to noise ratio .
Selectivity
±zo. 4 KHz wide (MlN) at 6 db down;
±35 KHz wide at 60 db down.
Altitude
-Bearing accuracy
To 55, 000 ft .
.
Manual 0. 50 degree; automatic
0. 50 degree.
SPECIFICATIONS
COLUNS 51R-6
CHARACTERISTIC
SPECIFICAT!Q~:
Power requirements
VOR operation
:!i. 5 volts. D-C, 1. -t5 amperes.
2,; ,·olts. -tO o Hz, 0.
!LS operation
~:; :~.:npere.
27. 5 volts, D- C, 1. 82 amperes.
26 volts, -tOO Hz, 0. 23 ampere.
VOR/ LOC performance:
Frequency r ange
'• . '
VOL. VI
..
108. 00 to 117. 90 MHz in 100 KHz
increments.
8-7
SPECIFICATIONS (continued)
COLLINS 51R-6
CHARACTERISTIC
SPECIFICATION
Sensitivity
Aural channel
a-microvolt input for 6-db S+N/N
ratio.
VOR channel
a-microvolt input for satisfactory
navigation performance.
Selectivity
40 KHz at 6-db points and 68 KHz at
60-db points with 3-db or less ripple.
Altit~de
Up to 45, 000 feet.
Spurious response
At least 70 db down.
Gain
100 milliwats output into a 600-ohm
load with a 5-microvolt input signal
modulated 30 percent with 1000 Hz.
AGC
3-db variation from 5-microvolts
"o 50.000 microvolts.
E"::!:qc.ency
st~b!li;y
0. D04 percent ::·om
(~50
to
o. OOG percent from
(- 1)7 to
}!avigation outputs
'•,
8 -8
..
~10
to
~s<> 'C
~131 •F).
-55 to Til "C
-160'F).
Five deviation indicator loads, four
flag indicator loads, two TO- FROM
l·o ads, and two RMI pointer loads.
VOL. VI
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R[ I [ R(HC[
S I ~HAl
,,. i 3<) 11z
10,440 ltz
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9960 Hz
')960 Hz
9480IIz
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" ' S ' A C£ .. o ouL.AfiOH
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or 30Hz
8 30\i
3~ AM (NOT SH OwN)
10 : 8~ AM (HO T $Hv wH)
llfCfiV[O
V0 R
S IGNAL
10, 440 Hz
..... lT I C IIOIITN
NOTE;
~OS I TIV(
"AXIMUM
SIQHALS All( Ill ~ ... ,,AT
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tLS(WH(II( AIIOUND TNt
STAT ION.
Or CYCLE
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8- 10
P HAS E
AN G L E
/
R E L AT I 0 NS H I P
\'OL. VI
BLOCK DL\GRAM THEORY OF OPERATION
VOR Ground Station
A basic understanding of the VOR ground station signal is necessary in order to
comprehend VOR system operation.
The ground station antenna system consists of an element that radiates an omnidirectional pattern, and an element or group of elements that radiate a directional
pattern rotated at 1800 RPM (30 Hz).
The 30 Hz reference signal consists of a 9960 Hz subcarrier frequency modulated
by a 30 Hz signal. The frequency modulated 9960 Hz subcarrier and then amplitude modulates the VHF carrier. This signal is radiated by t he omni-directional antenna. The 30 Hz variable signal is produced by the rotating directional pattern varying the signal field strength (space modulation) at the
receiver antenna.
RECEIV ED SIGNAL
.'
The received signal from the VOR ground station consists of a station identification signal and two 30 Hz modu lated components . The reference j)has e 3<; H:;;
signal has the same phase , regardless of the bearing from the aircraft :o t!lc
VOR station. T he variable phase 30 Hz s ignal varies degree-for-de,p:·ee wi:h
the magnetic beanng oi t!u; a irc-raft wi tn respect to t;-,e \'OR sta•ion .
The two signals are in phase when de t~cted by an airc :-aft rece i·.: er w!1ic:t is c.h.:e
no!:"tii of the st:l~ion (set: th~ 5igr.a: ?:~as e -~::glt.: Re lzL to nship illus tr:l::.3:1i .
E;;J.st c( tr.e
$ta:~o~;
:!1?
,:;;;r~lble pha~e
l3gs \te
r~:·c.-enc eC
Oy
~*' \ieg:~es .
So~:;:;
' ~ d~~
::ta::io:: ~nc :-.~·.) :; ,..;::j. .. _; a:-~· : ~u .::~~to; ~e~ s ..... ~:. -: :· ;:.. .. :1~ ~ . 'T~ ... . ·::;..::-.:.:.::..: : :~:~:l;. ~:
::!;·.: :r.i: !' r:r e ;·.::r.c~ :..~ · ::! i ..; '.:eg:~·f;~.:: :.i : ~ ;:cir.: ·::e~ : ->:· :~:·! ::;t:;.:it)n . A.>:;. :: .:::·-:!':-. ·
:~o:.·:;n
of ~ht- station llie~ a c i rc l..: ~l.Jck'.v ise :1.:0u~d t~~ s t3.tion, t: .2
i:nionsf:io of tl\o; :wo s ig:~als va r ies from li . ~gree~ .36;) degrees .
:-r..: : Jca; i~:er ~;.: vi..i :~J
:i l~ :i . .::i.
:·3.c :..J.:-::s o;.v-.;
~: .:t.! c:h.:;~~ - ~;r: .....Jns , on~
;.a~:> ~
..;::
~<l~ ;:
:· e-
-: . .;~·
of the airfield runway . v~e bea:n is modulated by a ~0 Hz signa !; the other is
modu la ted :)y a 150-Hz s 1gna!. T:te 90-Hz patte~" is dir ected along t he righ t
side of the runway ar.<: t~ e lii ll -Hz j)atter n on t he left ~ ice . The relative ar:1plitude of the 90-Hz to the 150-Hz signal varies with the horizontal ?Osition of t he
a ircraft in respect to the instrument approach path. In the center of the approach
path the beams " '·er lap and iorm an area wh~re the t\vo s ignals are of equa l
strengtn.
The amplitude of the two signals are compared in the receiver, and an off-course
deviation signal is produced when an amplitude difference exists. The deviation
signal Is selected for use by the flight diirector system wh~n ··voR-ILS.. is
selected on the navigation selector panel.
\.O L . VI
LOCAL I ZER CtHTtR
LOCALIZER
ANTENNA
PATTERN
RF SECTION 806A WILCOX
·The RF section of this receiver uses a double conversion system consisting of
oscillators and miXers to develop a 10.7 MH:z fixed frequency IF. The RF
circuits have a 10 MHz bandwidth which eliminates the need for tuning . Only
the crystals of the oscillators nee'! be chang·e d to effect a channel change.
Channel selection is accomplis hed by switching crystals in the oscillator~
used to develop mixer injection voltages . A:n all electronic crystal switching
arrangement which requires no mechanical switching is used. When the desired operat!.."lg fre(i~ency is selected at ~!'!e .ccntrol panel, :he prc?er C!"Y3t:.l:
is s e~ected ty d.iodes oper~ti:-:6 ~s sw::~hes.
::'.):ic·::i!::; :::.e co~1·:e !·.iiOn c:.-c'..i•ts ~=e i·i~·e ~·...!. 7 :\iriL iF a~p!~·:e :·:: . T:1~ .-.GL
p:-ov ide Automatic Cain C..:>rarol \AC':, u;> to a t)recie ~et·mined ievel :..:>
the second and fOI.t!"th lF stages. Above a predetermined level ACC is r2moYed
!r?rr. :::~ :E' .;::1.g·~s ar.r: :.;J?:it!:: : :1 :!:-:> ··:·:·c:H er1c! .. St:!.:;es . -:'~~ !7 ~1~cl:!:er
c.~:t--:.t: .s Jf:~ectc:c !.>)" a t..lvcc c.:.- ~ec :~.r .vr. lC!'l .reJroCuce.s i.:'!~ rtit::!"~!~CC :1nci Yl.riable i)hase signals when VOR signals are bei:tg received. In localizer ·: >peration
the detector output i.s the ~0 Hz and !;)0 Hz localizer signals. Stauon identilicat:on audio is sent to audio amplii.i.ers in the receiver before application :x> t he
aircraft interphone system. The VOR or localiZer signals are applied to :h<!
manual omni-localizer and automatic omni sections of the receiver.
c!:~uits
MANUAL SELECTION
The manual o mni-locali.zer section contains a variable phase channel , reference
·····-···
8-l2
..
VOL. VI
.
<
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0
.
Rf' SE CT I ON
--
£
50KIIz
OSCILLATOR
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TO
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RCVR
1
67.09 OR
67. 141-1Hz
I
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r - -- ·
UNIT
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1 108.0-1 17 . 95HH l
INJECTION
MC
OSCILLATOR
HIXER
6 1 .4-62.35
-MHz
15 .624.8 1-!Hz-
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IF
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AUDIO TO
INT ERP'HOM £
SYSTEH
AUDIO
ANPllf i ERS
----MANUA L
COHPOS I TE 9960tiz
AND 30Hz SICNAL S
WARNING
DEVIATI ON
AND TO• FIIOH
OHNI -lOC
SECTION
AUTOMAT IC
ONN I
SECT I ON
8 l 0 CK
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VHF'
NAV
Votl IIUR I NG
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phase channel, and localizer channel. In VOR operation·the reference phase
and variable phase signals are applied to their respective channels. The
reference phase signal is a Frequency-Modulated (FM) sub-carrier which is
amplified in the reference phase channel. After ampl;Iication and limiting,the
30Hz modulation is reproduced in an FM detector. The 30Hz reference
signals is then applied to a resolver in tbe HSI. The position of the resolver
rotor is determined by the selected VOR course (COURSE SET knob position).
The selected course of the resolver phas.e shifts the 30 Hz reference phase
signal. The resultant signal is amplified and applied to a phase comparator .
The variable phase 30 Hz signal is amplified and also applied to the phase
comparator. The comparator circuit develops a polarized D-C output when the
two signals are not in phase. This po larized signal provides deviation information to the HSI and flight director system. The reference phase signal, with
selected course information added, is also compared with the variable phase
signal in the to-from circuit. The phase relationship of the two signals pr oduced
a polarized D-C output. The polarity of this DC determines the to-from display
position. In localizer operation the signal is processed by the localizer channel.
The receiver section supplies an audio signal containing a 90 Hz component and
a 150 Hz component. After amplification, the c omposite audio signal is separated into 90 Hz and 150 Hz components by fixed tuned filters. The two audio
components are rectified and when the resultant voltages are equal in amplitude,
the output voltage will be zero . T his indlicates an aircraft on-course condition.
When the two signals are unequal in amplitude, a polarized deviation (err or )
signal will result. The deviation output is applied to the HSl deviation bar.
AUTOMATIC SECTIOC\'
The automatic omni section of th.e rec eive~ also has a refe:<:nce p!lase channe:,
variable phase channel, and iJh<:.se comparator. The operation of these co1ar.::eis
!s si!':'!ila.r LO the r:tar.ual o:nni- !oc~liZ:..:!· _j~C::ton. H~wcve:-, S!i ~:.ttOI:~:t\iC i!: stru:ncntaio:-: ser·:c !oc·p :::.:.3 bet:::: ac!deti . T~~~ CO!:~~:l!":lt..:> r a...:~ ·>tr:.atic:l~~y ant~
continuously ~ump~r~s· ~h.;: r~i~re n<:e oi• ~sc anc:! \·ariable ~n~5 ~· .iigna~s . 7:!<..'
comparison is used to positior. a differ en : ial synchro which transm its beanng
information to the BDHl' s and HSl. When the variable phase and reference
phas·~ ~:u:e !'lOt i:t pi~a.st , t!!€: ~<,tn ~t!=-~~.J~· deYI':l-:>p;; o. ~~;)b.!'iZ i!C D-C c ·.tt~:r-.~:. . '!'1:-?
D-C vo ltage 1s com·erted :o an A-C slgna i whose phase lS d~tl!~mmed by th<:
polarity of the comparator output. The A-C voltage is amplified and used to
drive an A-C motor. The direction of motor rotation is dependent upon the
phase of the applied 'loltage. This gives sense of direction to the loops. The
motor positions the resolver in th~ reference phase channel until the reference
phase and variable phase signals are in phase. As the two signa;s approach an
in-phase condition, the comparator output decreases to zero and the motor stops.
A differential synchro is positioned by the motor and transmits bearing information to the BDHI's and HSl. Assuming •hat a bearing of 90 degrees exists
··-
8-14
VOL. VI
'
I
, <:
0
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COMPOSITE
AUDIO INPUT
9 960Hz
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between the aircraft and VOR station, the variable phase signal then leads the
reference. phase by 90 degrees. Therefore, the comparator circuits develop an
output. This results in the motor driving the reference phase resolver 90 degrees to bring the two signals in phase. The 90 degree shaft rotation is transmitted to ~he bearing pointers of the indicators by a differential synchro. This
synchro is supplied excitation from the compass system; therefore, the synchro
?utput is bearing relative to the indicato·r compass card.
RECEIVER SECTION 51R-6 COLLINS
The. RF section uses a triple conversion. system consisting of oscillators and
mixers to develop a 500 KHz IF. Solid stage switching of oscillator crystals
is used for frequency selection requiring no mechanical switching. The IF
signals are transformer-coupled through four stages. of amplification 'to the de-·
tector. The detector output is applied to the AGC amplifier, noise limiter and
VOR/LOC output terminals.AGC voltage controls the RF amplifier and the first
two IF stages. The noise limiter output is coupled through four audio amplifiers
before going to the aircraft interphone s.ystem. The VOR/LOC signals are sent
to the manual and automatic instrumentation units .
MANUA~
INSTRUMENTATION UNIT
The manual instrumentation unit has two channels, reference and variable. The
composite VOR signal consists of the 9960 Hz FM subcarrier containing the 30
Hz reference signal and the amplitude modulated 30 Hz variable signal. The
composite signal is routed to the inputs of both the reference and variable cllnnels . The variable 30 Hz signal is separated by a low pass filter in t.'le variable
channel. The variable signal is amplified, filtered to remove any 30 Hz barmonies and further amplified to the power level required by the variable channel
inpu~ circuitry of the deviation and to-from phase detectors.
In ~he reference channel :he composite VOR signal goes througb stages oi amplification and limiting. The limiters eliminate all effects of amplitude modulation (variabie signal) from the composite VOR signal. After the amplification
and limiting stages , the 9960 Hz sub- carrier is detected to recover th(' refere:tce
30 Hz si;o~::.: ~rom the r efe rence 3\l Hz detccto:- and one ou:put is ro u:ed to th!!
autoresolver driver for use in the automatic instrumentation unit and the selftest circuits. A second output is routed through the manul!-1 resolver through
the manual resolver driver to the OBS r-esolver in the HSI. The rotor of the OBS
resolver is manually positioned by setting in the selected VOR course (radial)
with the course set knob. Rotating the course knob (resoiver rotor) phase shifts
the reference 30 Hz signal degree per degree with s elected course (Inherent
phase shift of the resolver and associated circuitry is 90 degrees with no deviation from selected course). The phase shifted reference signal is amplified
and filtered to remove any 30 Hz resolver generated harmonics, and applied to
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the deviation and to-from phase comparators.
The deviation phase comparator produces a D-C error voltage proportional to
the pbase difference between the reference and variable signals. The error
voltage output of the pbase comparator is routed to the HSI deviation bar,
driving it left or right depending on the error signal polarity. The reference
and vari,a,ble signals are also summed in the pbase comparator and used as
flag warning. Loss of either or both of the 30 Hz signals will reduce the flag
signal level enough to allow the VOR/LOC flag to appear. The 90 degree phase
shifted reference signal from the OBS resolver is shifted an additional 90 de grees before application to the to-from pbase comparator. The reference and
variable signals are in phase or 180 degrees out of pbase. When the signals are
in pbase,the to-from phase comparator will drive the indicator to a "TO" indication.
A 180 degree pbase relationship wlll pro¥ide a "FROM " indication.
LOCALIZER
When a localizer frequ!_ncy is selected, a diode switch allows the localizer signals to be amplified and applied to the 90 Hz and 150 Hz filters. The two signals
are AM and are compared in the localizer output circuits to produce a deviation
signal. Th.,. amplitudes are summed to produce a localizer reliability flag signal. During localizer operation diode switches turn off the output amplifiers of
the manual and automatic instrumentation units.
AUTOMATIC INSTRUMENTATION UNIT
The reference signal is applied to the autoresolver, amplified and sent to the
VOR phase comparator in the auto-instrumentation unit. The variable signal is
amplified and compared with the reference signal in the phase comparator. T!le
D-C output of the comparator is sent through a filter ;and chopper (D-C t~ A-C
inverter) amplified and drives ~~e servo motor. The servo motor repositio:1s
me autorl!solver rotor until the reference and variable phase sign.31s are in
quadrature (90 degree phase difference). A differential synchro is also pos i tioned mechanically by the motor. The differential syncbro ~om pares magnetic
headir.g with rotor shaft pos ition and se:~ds a syn~h:·o ou~pu~ :o tl:e BDH! ar.d ESI
bearing pointers.
SYSTEM PECULIARITIES
The Localizer deviation signals are sent to the AWLS systeon during an AWLS
approach. The deviation signals are desensitized before being applied to the
flight director instruments. The localizer antenna switch is also activated by the
AWLS system. At localizer beam center the rear VHF anten.na is disconnecbed
from the system and the nose VHF antenna inserted.
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