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Патент USA US2410117

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Oct. 29, 1946.
2,410,117
J. D. WESTON
VISUAL INDICATOR FOR RADIO BLIND APPROACH SYSTEMS
Filéd May 4. 1945
WI
R2
‘
I véntor
£40m
3%:67P?»?;
'
Attorney
2,410,117
Patented Oct. 29, 1946
UNITED STATES PATENT orrics
2,410,117
VISUAL INDICATOR FOR RADIO BLIND
APPROACH SYSTEMS '
J e?'rey Dennis Weston, London, ‘England, as
signor to Standard Telephones and Cables Lim
ited, London, England, a British company
Application May 4, 1943, Serial No. 485,614
In Great Britain May 11, 1942
8 Claims.
1
.
2
,
.
The description‘will be given of the invention
This invention relatesto a method of and ar
rangements for distinguishing visually between
as applied to a radio'blind approach system.
two signals of the same rectangular wave form
but whose variations are of opposite sign and is
‘Referring to Figure 1, the arrangements ac
cording to the invention comprises a recti?er
particularly applicable to visual indicating ar
rangements for radio blind approach systems of
the kind in which an approach path is de?ned
by the intersection of two overlapping lobes, com
plementary signals being transmitted by the two
bridge RB comprising four recti?ers r‘! . . . 74
'
connected as shown, the output circuit of the am
pli?er valve V being in series with a resistance
R2 and the indicating instrument A across one
diagonal of the bridge. The primary winding" L
of va transformer T is connected acrossthe other
radiations so that the signals received on the
approach path constitute a continuous dash, or
no apparent signal.
diagonal of the bridge. The secondary winding
of ‘the transformer T is ‘centre-‘tapped at P so
that two equal'but oppositely phased alternating
One indicatingarrangement for this type of
voltages appear across the two halves‘ of ‘the sec
system'utilises a dynamometer type of indicating
instrument. Such an arrangement is described in 15 ondary Winding relative to the point P. These
two portions of ‘the secondary winding are‘ con
nected in push-pull‘fashicn to a di?erential rec
British Speci?cation No. 526,114. The present in
vention aims at provid'mg an indicating arrange
ment utilising a direct current moving coil in
ti?er system comprising recti?ers WI and W2.
The parallel‘ feed for the 'recti?ers WI and W2
dicating instrument. Previously known indicat
ing arrangements vfor blind approach systems of 20 is provided by the alternating voltage across the
the type speci?ed which utilise direct current
moving coil indicating instruments depend for
satisfactory operation upon a balance between
two recti?ers or two thermionic valves.
resistance R2 and A‘ in series.
Referring now to Figure 2 ‘of the drawing, curve
a and curve I) show graphically dot and dash sig
nals respectively, which would be obtained, one
on each side of the approach path after demodu
lation from the radio carrier-of the received sig
Such a
balance is generally intolerable, since a slight dis
turbance of it, which may be caused by atmos
pheric or other changes gives rise- to a false in
nals.
Curves c and d show the results after the
direct current component has been removed from
dication.
According to the present invention the method
thesignals represented by a and b respectively.
of distinguishing visually between two signals of 30 This vdirect current component is removed by
the same rectangular wave form but Whose varia
means of the resistance RI and capacity Cl which
form a ?lter which passes all frequencies at and
above the dot and dash ‘frequency. The curves
0 and d therefore represent the unrecti?ed cur
tions are of opposite sign comprises developing
from either signal a comparison signal of con
stant sign and combining this comparison signal
with the original signal to obtain a direct cur
rent flowing through the resistance R2 and in
strument A and the recti?er bridge in series with
the latter. It will be observed that the two signals
direct current to obtain an indication of its sign.
represented by c and d of Figure 2 are similar
Arrangements for carrying out this method
but Whose variations are of opposite signs. Curve
comprise means for obtaining from the signals M c Figure 2 represents the voltage produced by the
of rectangular waveform a comparison signal of
full-wave recti?er bridge across its load, winding
constant sign irrespective of the sign of the sig
L of transformer T, and is independent of
nal variations and arrangements for combining
whether dots or dashes are being received, that
the comparison signal of constant sign with the
is‘, it is the same for both currents represented by
original signal in a differential recti?er device,
c and d but the corresponding voltages across R2
rent signal whose sign depends upon the sign
of the original signal variations and applying said
and a direct current indicating instrument sen
will be as shown in c or 41 according as dots ‘or
sitive to direction of current ?ow therethrough to
which the differential output is applied.
The invention will be better understood from
the following description taken in conjunction
with the accompanying drawing in which
Figures 1 and 3 show diagrammatically two em
bodiments of the invention, and
dashes prevail in the received signal.
of the secondary winding of the transformer T
since the transformer acts to pass substantially
all frequencies but zero frequency, i. e. direct cur
rent. The wave in the other half of the second
ary winding of the transformer T will be. curve
Figure 2 shows several curves referred to in
the description.
'
Curve I
Figure 2 represents the recti?ed wave in one half
1‘ reversed about the zero line.
55
I
.
The resistance 32 is preferably adjusted to such
2,410,117
3
a value that the voltage across it has approxi
mately the same amplitudes as that across each
half of the transformer secondary winding.
Thus one recti?er WI or W2 receives the differ
ence between the voltage across R2 and that
across one half of the secondarywinding of T
this diilerence being substantially ’ zero. The
other of the two recti?ers WI or W2 receives the
sum of the voltages across R2 and its associated
half of the secondary Winding of T. Thus the
indicating instrument receives a series of pulses,v
representing the dot signals and will be in one
direction or the other according to the sign of
4
approach path is de?ned by the intersection of
two overlapping lobes complementary signals
being transmitted by the two radiations com
prising means for obtaining from the received.
signals a comparison signal of constant sign and
a differential rectifier arrangementto which the
comparison signal and the original signal are
applied, to obtain a direct current of appropriate
‘ . sign depending upon the sign of the original sig
the Variations of signal 0 or d applied across R2.
When the meter is suitably damped a steady de
?ection on one side or the other of zero is ob
nal variations, and a direct current indicating in
strument sensitive to the sign of the current ?ow
ing therethrough to which the said direct current
is applied.
4. Arrangements as claimed in claim 2 wherein
said means for obtaining a comparison signal
comprises a recti?er bridge across one diagonal
of which the said signals of rectangular wave
form are applied and a load impedance across
tained according as dot signals or dash signals
prevail thereby giving an indication as to which
side of the approach path the receiver is located.
When on the approach path a signal of constant
amplitude or continuous dash is received and the
recti?er system is not energised since the ?lter
formed by RI' and CI does not pass any direct
current, and no de?ection of the indicating in
strument can occur due to signal reception.
25
wave form but whose variations are of opposite
sign, means for obtaining from the signals a
upon an exact balance between recti?ers or other
comparison signal of contant sign irrespective of
the sign of the signal variations, said means for
obtaining a comparison signal comprising a recti
Referring now to Figure 3, an alternative em
bodiment of the invention is shown. The trans
former of the arrangement shown in Figure l is
?er bridge across one diagonal of which said
signals of rectangular wave form are applied and
a load impedance across the other diagonal of
the bridge from the terminal of which the com
It will beobserved that the system according
to the invention does not depend for its reliability
components.
replaced by a resistance~condenser network. The
bridge recti?er Works into the load resistance R3
and the direct current is removed by the two
equal condensers C4 and C5 in conjunction with
the equal resistances R4 and R5 respectively.
These elements provide the push-pullinput to
the differential recti?ers WI and W2 and the
operation is similar to that described in connec
tion with'Figure 1, a repetition of it being con
sidered not necessary in connection with Figure 3.
Whilst two embodiments of the invention have
been disclosed by way of example, other embodi
ments which fall within the scope of the invention
as de?ned in the appended claims will occur to
those skilled in the art.
What is claimed is:
1. In an ‘arrangement for distinguishing visu
ally between two signals of the same rectangular
current wave form but whose variations are of
opposite signs which comprises means for de
veloping from either signal a comparison signal
current of constant sign, means for combining
this comparison signal current with the original
signal current to obtain a direct current signal
whose sign depends upon the sign of the original
signal variations, and means for deriving from
this direct current signal an indication of its
sign.
2. In an arrangement for distinguishing visu
ally between two signals of the same rectangular
waveform but whose variations are of opposite
sign, means for obtaining from the signals of
rectangular wave form a comparison signal of
constant sign irrespective of the sign of the sig
nal variations and arrangements for combining
the comparison signal of constant sign with the
original signal comprising a differential recti?er
device, and a direct current indicating instrument '
sensitive to the direction of current ?ow there
through to which the di?erential output is
applied.
.
-
3. Visual indicatingvarrangements ‘for radio
blind'approach systems of the kind in which an
the other diagonal of the bridge from the ter
minals of which the comparison signals of con
stant sign are obtained.
5. In an arrangement for distinguishing visu
ally between two signals of the same rectangular
parison signal is obtained; means 'for combining
the comparison signal of constant sign with the
original signals comprising a differential recti?er
device, said recti?er device having a resistance
and a direct current indicating instrument sen?
sitive to direction of current flow therethrough
included in series with the rectifier bridge and in
parallel with the arms of the di?erential recti?er.
6. Arrangements as claimed in claim 5 wherein
said load impedance comprises a transformer,
the secondary Winding of which is centre-tapped
and the two halves of said secondary winding feed
respective arms of the differential recti?er.
I
7. In an arrangement for distinguishing visu
ally between two signals of the same rectangular
wave form but whose variations are of opposite
sign, means for obtaining from the signals a com
parison signal of constant sign irrespective of the
sign of the signal variations, said means forob
taining a comparison signal comprising a recti
?er bridge across one diagonal of which said sig
nals of rectangular wave form are applied and a
load impedance across the other diagonal of the
bridge from the terminals of which the compari
son signal is obtained, said load impedance com
prising a resistance, means for combining the
comparison signal of constant sign with the origi
nal signals comprising a differential recti?er de
vice, means for applying the voltage changes at
the ends of said resistance to the respective arms
of the differential recti?er device, said recti?er de
vice having a resistance and a direct current in
dicating instrument sensitive to direction of cur
rent ?ow therethrough included in series with the
recti?er bridge and in parallel with the arms of,
the differential recti?er device.
.
.
8. Arrangements as claimed in claim 7, wherein
said last mentioned means comprises series con
nected capacity and resistance combinations in
shunt across the respective ends of said load re
sistance and a reference point.
-
JEFFREY DENNIS WESTON. '
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