Note: Descriptions are shown in the official language in which they were submitted.
1322037
~ 1
AIRBORNE RECEIVER IN MICROWAVE LANDING SYSTEM
WITH CHANNEL SELECTION MEANS BY MANUAL INPUT
j OF FAMILIAR ABBREVIATIONS OF AIRPORTS
Backaround of the Invention
1) Field of the Invention
The present invention relates to a microwave
landing system (MLS) and, in particular, to an airborne
receiver for use in the MLS.
2) Description of the Prior Art
As a standard of a landing system for guiding an
aircraft onto a runway with safety, the instrument landing
system (ILS) has been used for a long time. Recently, the
15~ MLS has been~proposed as one which will take the place of
the conventional ILS, and used for practical tests.
Reference is made to "MLS is OPERATIONAL" by W. C. REED,
August 1984, Allied Bendix Aerospace (Reference 1) and
"Introduction to MLS", October, 1987 by United States
Department of Transportation Federal Aviation
;Administration Program Engineering and Maintenance Service
(Reference 2).
... .
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The MLS comprises MLS ~round stations injtalled
at airports and airborne receiver~ carried on aircraft,
The M~S ground stations transmit MLS signals of
frequency bands or channels individually assigned
5 thereto. The frequency band o~ 5031 ~ 5090.7 MHz and
20Q channels ~f channel Nos. 500 to 699 are provided to
be a-qsigned to individual MLS ground ~tations o~
airports. When an aircraPt approaches a destinat~on
airport, the aircraft receives a particular MLS channel
10 signal from the MLS ground station of the destination
airport by its air~orne receiver which is called "MLS
receiver" so as to kn~w the azimuth, the elevation and
distan~e to the destination airport.
The MLS receiver comprise.q a ~uning circuit or a
lS channel selection circuit and a tuning dial or a channel
selection dial in order to selectively receive a desired
one of the individual MLS channel signals. In a
conventional MLS receiver, the channel selection circuit
is a ~uperheterodyne type which comprises a local
2~ oscillator of a frequency synthesi~er type and a mixer.
The oscillating frequency of th~ local oscillator is
adjuste~ by the channel selection dial. When the
alrcraft approaohes the destination airport, an operator
or a pilot of the aircraft must manually operate the
~: 25 channel selection dial of the MLS receiver to ~elect the
particular MLS channel of the MLS ground station of the
destination airport. As a result, the channel ~elect~on
circuit i8 adjusted to tune the MLS rec~i~er to the
l322n37
particular MLS channel to thereby receive the particular
MLS channel signal. More in detail, the local oscillator
is adjusted by the manual operation of the channel
selection dial to produce a particular local signal of a
particular local frequency which is applied to the mixer.
The mixer combines the particular local signal with the
particular MLS channel signal to frequency convert the
particular MLS signal to an intermediate frequency (IF)
signal of a fixed IF frequency. Thus, the MLS receiver is
tuned to the particular MLS channel and the particular MLS
channel signal is obtained as the IF signal from the
channel selection circuit.
However, since it is difficult for the pilot to
remember the channel numbers and/or transmitting
frequencies of the MLS ground stations of all of the
airports, he must use a list of the channel numbers and
names of the airports prior to operation on the channel
selection dial. It is complicated for the pilot to refer
to the list.
Summary of the Invent ion
According to the present invention, an airborne MLS
receiver is provided wherein the MLS channel selecting
operation of the destination airport can readily be
; performed without use of the list.
According to the present invention, an airborne MLS
receiver is provided wherein the channel selection can
readily be performed by setting an abbreviation of airport
1322037
name of or a station code of an MLS ground station of a
destination airport to the receiver which is familiar to
the pilot.
An airborne MLS (Microwave Landing System) receiver
for use in an MLS environment, according to the present
invention, comprises input means for directly manually
inputting one of a number of different character
abbreviations of destination airports wherein the
abbreviations are commonl~ known by pilots operating the
receiver; storage means for memorizing a table of channel
: .selection codes of MLS channel numbers assigned to
respective MLS ground stations at different airports
together with corresponding character abbreviations of the
airports, the storage means being coupled to the input
means and responslve to the input character abbreviations,
and means for reading a particular one of said channel
selection codes of MLS channel numbers corresponding to an
input character abbreviation from the table; and a channel
selection circuit for selecting a desired MLS channel for
reception of corresponding MLS channel signals from a
particular ground station at a destination airport,
comprising a control circuit coupled to the storage means
and responsive to the particular channel selection code
; ~read from the table, for enabling selection of the desired
: :~25 MLS channel and reception of the corresponding MLS channel
~signals.
13220~7
According to a preferred aspect of the invention,
the channel selection circuit of the MLS receiver comprises
a local oscillator of a variable frequency type for
oscillating a local signal of a controlled frequency and a
mixer circuit for mixing a specific one of the MLS channel
signals and the local signal to convert the specific MLS
channel signal to an intermediate frequency (IF) signal of
a fixed IF frequency and to receive the specific MLS
channel signal, wherein the control means is responsive to
the particular channel selection code and controls the
local oscillator to generate the local signal having a
particular frequency as the controlled frequency, the
particular frequency being equal to a particular difference
frequency between the specific MLS channel signal and the
IF signal, wherein the mixer circuit converts the specific
MLS channel signal to the IF signal.
According to still another aspect, the input means
is a conventional alphabetic keyboard.
Brief Descri~tion of the Dra~in~s
Fig. 1 is a block diagram view of a main part of an
MLS receiver according to an embodiment of the present
invention;
Fig. 2 is a table of airport abbreviations and
channel selection codes memorized in a storage means; and
,
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Fig. 3 i6 a block diagram view of an example of
a local o~cillator.
Descrlption of the Preferred Embodiment
Referring to Fig . 1, the MLS receiver ~hown
5 therein comprises a radio frequency (R~) bandp~
filter ~BPF) 11 for filtering the MLS frequency band
signal from an incoming si~nal through an antenns 10.
The MLS freguency band signal is applied to a channel
~election circuit 12. In the pxesent embo~i~ent, the
10 channel ~election cirouit 12 i6 the 6uperheterodyne
type and comprise~ a local oscillator 13 and a mixes
: 14.
~ n the prior art, a channel selection dtal i6
provided to ad;ust an oscillating ~requency o~ the
15 looal oscillator 13 to:select a desired on~ of the MLS
channelc, and the desired MLS channel signal i~
- obtained a8 the IF ~ignal ~rom the channel selection
~ .
~ . ¢ir¢uit 12, as de~cribed in the preamble.
:: : The IF signal is amplified at an IF ampli~ier
20 ~AMP) 15 apd is therea~ter prooessed at a proo~Jsing
circuit ~not ahown) which ~ known in the prior art.
he ML8 reoeiver acoording to the present
. ~ embodiment comprises an input unit 16 and a storage
u~it 17 in place of the channel selection dlal.
The input unit 16 i~ a key~oardr for example, a
conventional alpbabetic keyboard ~or inputting an
: abbreviation of an airpcrt name or a keyboard
oomprising a plurality o~ keys correqponding to
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airports with identification of the airport name
abbreviations.
The storage unit 17 previously memorizes a table of
abbreviations of airport names and channel selection codes
for selecting MLS channels of the corresponding airports,
as shown in Fig. 2.
Now, operation of the storage unit 17 will be
described in connection with, for example, the Wexford
County Airport in Cadillac City, Michigan, U.S.A. The
airport has an abbreviation of ~CAD~.
Referring to Fig. 2, the abbreviation ~CAD" is
shown in an abbreviation section in a table of Fig. 2. A
corresponding code "m(602)~ is a channel selection code for
selecting the MLS channel (No. 602) of the MLS ground
station of the Wexford County Airport.
The storage unit 17 responds to an airport name
abbreviation from the input unit 16 and converts it to a
corresponding one of the channel selection codes which is
applied to a control circuit 18 in the local oscillator 13.
The control circuit 18 is responsive to the corresponding
channel selection code and controls the local oscillator 13
to produce a particular local signal of a particular local
frequency which is applied to the mixer 14. The mixer 14
combines the particular local signal with a particular MLS
channel signal to convert the particular MLS signal to an
IF signal, in the similar manner as the
,:
,,~
~'~
'
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conventional channel selection circuit of ~
~uperheterodyne type as described in the pre~mble.
Now, it is asjumed that the MLS receiver has
the fixed IF requency of 160~8 MHz. When the
S abbrevistion "CAD" of the airport is set at the input
unit 16, the stora~e unit 17 applles the corresponding
channel selection code "m(602)" to the control clrcuit
1~. The channel number o the airport i8 602 which i5
corr~ponding to a frequency of 5061.6 MHz. In order
10 to receive the MLS ~ignal of 5061.6 M~, the local
oscillating frequency in.the receiver is set at 4900.8
M~z which is equal to (5061.6 M~z - 160.8 MHz).
Therefore, the control c$rcuit 18 controls the l~cal
osclllator 13 to produce a particular local 6i-gnal
15 ~hich has a ~requency of 4900.8 NHz. The particular
local cignal of 4900.8 MRz is applied to the mixer 14,
from which the ~L~ chan~el 5ig~al ~rom the ~CAD"
airport is obtained as the I~ signal. ~he IF signal is
~pplied to the IF amplifier 15.
Re~erring to Fig. 3, the local oscillator 13
may be a frea~uenoy synthesizer which comprl~es a fixed
~re~uency oQcillator 19 for o~cillat~ng an 06aillating
signal of a fixed ~requency of, for exa~ple, 10 M~z, a
counter or fixed frequency divider 20 or frequency
25 dlviding the osciliating signal at a fixed d~viding
ratio of l/M (M = 200) to produce a divided signal, a
phase locked loop, and a multiplier 21 with a
multiplyinq ratio of, for ~xample, 6.
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I
The PLL comprises a voltage controlled
oscillator ~VCo) 22 ~or oscillating a VC0 signal, a
variable frequency di~ider 18' as the con~rol circuit
for frequency dividinq the vco signal at a dividing
5 ratio set thereat to produce a ~ariahle frequency
divided signal, a phase detector 23 or comparing the
divided signal and the trariab~ e frequency divided
signal to detect a phase difference therebetween as an
¦ error signal, and a loop ~ilter 24 for re~oving a high
10 frequency signal component to derive the erxor signal
which i~ applied to the VC0 22 so as to stabili~e a
frequency of the VC0 signal.
~ he variable frequency divider 18' i9 a
pro~rammable counter to which a variable dividing ratio
15 is Qet as the channel sele~tion codes by the ~torage
, unit 17. In re~pon~e to input of an airpor~ name
; abbreviation at the input unit 16, a corresponding
dividing ratio i~ delivered ~rom the storage unit 17 to
set it in the frequency divider 18'. The dividing
20 r~tio is applied to the frequency divider 18' from the
storage unit 17 to control a frequency of the VC0
signal~ Then, the VCO signal is fr~quency multiplied
by 6 at the multiplier 21 to produce the local ~ignal.
In this aonne~tion, th~ dividing ratio~ as the
25 channel selection codes are previou~ly determined with
refer~nce to the fixed frequency of the fixed frequency
: oscillator 19, the ~LS chann~ls, the IF frequency,
~' 1 1 . ' : .
i,~,,.,~
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dividlng ratio, and the multiplying ratio, as shown in
the following table.
TABEE
Channel ~umber S00 ¦ 602 .
5 Frequency ~MHz) 5031 ~ 5061.6 5090.7
_
Fixed Freq~enoy (MHz) 10
~ixed Dividing Ratio ~Mj 200
Varl ble Dividing _ 16Z34 ¦16336 ~16433
VCO Frequency ~MHz) 811.7 ¦ 816.B ¦ 821.65
10 Multiplying Ratio 6
Controlled Frequency 4~70.2 ¦ 4900.8 ~ 29.9
_ IF Frequency (MHz) 160.8
Alrport name abbreviations are used in the
above-mentioned embodiment, but alphabetic station
15 codes of the MLS ground station6 of the airports, whioh
are ~a~iliar to pilots, can be us~d in plac~ of the
airport name abbreviations. For in tanoe, the MLS
ground statlon at the "CAD~ airport has an alphabetic
station code "MAJ~ herefore, ~MAJE" is described
20 ad~acent "CAD" but with a parenthe~is in the ta~le o~
Pig. ~.
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