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Патент USA US3051939

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Aug. 28, 1962
J. F. SULLIVAN
3,051,928
PULSE PAIR DECODER
Filed June 30, 1959
l
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2 Sheets-Sheet l
301‘15
FALSE DECOD/NG PULSES
E: ÜATA‘LINK PULSE, /8405 SPHC'ING
I:|= DME PuLsE, /aqs smc/N6,
INVEN TOR.
JÜHN F. öULL/VAIY
BY
AGENT
Aug. 28, 1962
J. F. SULLIVAN
3,051,928
PULSE PAIR DECODER
Filed June 30, 1959
2 Sheets-Shee’rl 2
United States Patent O
ICC
3,051,928
Patented Aug. 28., 1'962
l
2
3,051,928
pulses is the given pair of pulses, and means to produce
an output when the detected pair of pulses is the given
PULSE PAIR DECODER
John F. Sullivan, Bloomfield, NJ., assigner to Interna
tional Telephone and Telegraph Corporation, Nutley,
NJ., a corporation of Maryland
Filed June 30, 1959, Ser. No. 823,967
6 Claims. (Cl. 340-167)
This invention relates to signal decoders and more
particularly to a decoder for generating an output signal
upon occurrence of a given pair of pulses spaced a pre
determined tirne interval having particular utility in, but
not necessarily restricted to, TACAN (Tactical Air Navi
gation System).
TACAN is a polar-coordinate navigational system by
means of which an aircraft measures its bearing and dis
tance with respect to a surface beacon to which it is
tuned.
p
For distance measurement, the airborne trans
mitter transmits interrogating pulses. The surface beacon
receives these pulses and transmits replies automatically
over the ground-t'o-air channel and by measuring the time
elapsed between its transmitted pulse and the received
reply, the airborne receiver computes the radio travel
time and hence the line-of-sight distance between the air
pair of pulses.
Another feature of the present invention is a decoder
of the type described wherein the means to detect the
pair of pulses spaced a predetermined time interval in
cludes a delay line having a plurality of taps spaced
therealong at given time intervals.
Still another feature of the present invention is a
decoder of the type described wherein certain taps along
the delay line are coupled to a means to produce an out
put signal in response to the detected pair of pulses, and
certain other taps along the delay line are coupled to a
means which will detect Whether the detected pair of
pulses is said given pair of pulses and will produce a
control signal in the absence of said given pair of pulses
to prevent the production of said output signal.
The above-mentioned and other features and objects of
this invention will become more apparent by reference
20 to the following description taken in conjunction with
the accompanying drawings, in which:
FIG. l is a series of waveforms illustrating the false
decoding problem relative to this invention and useful
in explaining the operation of the embodiment of FIG.
craft and the surface equipment. The transmission in
2; and
both- directions is by pulse pairs with 12 microsecond 25
FIG. 2 is a schematic diagram of an embodiment for
spacing, hereinafter referred to as DME (distance meas
a decoder for detecting a given pair of pulses in accord
uring equipment) pulses or pulse pair.
ance With the principles of this invention.
The precise location in time of roughly 50 percent of
The TACAN receiver is capable of receiving DME
the pulses transmitted from the surface beacon does not
pulse
pairs and data-link pulse pairs. The DME pulse
30
affect bearing and distance measurement. Thus, a small
pairs have a time spacing of 12 microseconds on centers
percentage of the surface beacon pulses may be arranged
while the data-link pulse pairs have a time spacing of 18
into code groups to provide additional information. The
microseconds on centers. Since it is possible for the
additional information can be transmitted from or to the
TACAN receiver used by the TACAN data link to re
aircraft and may be altitude, air speed, identity, or land
ceive both DME pulse pairs and data-link pulse pairs,
ing instructions. The communication mode of TACAN 35 there is a probability of a false 18 microsecond pulse
is called TACAN data link. The data-link transmission
pair existing at the input to the decoder employed to
from air to ground is by pulse pairs with 18 microsecond
recover the data-link pulse pairs through combinations
spacing, hereinafter referred to as data-link pulses or
of DME pulse pairs and data-link pulse pairs or com
pulse pair.>
»
binations of DME pulse pairs with each other. This re
One of the components required by TACAN data-link 40 sulted in false decoding since prior art decoders are in
ground receivers is a decoder which filters out interfer
capable of determining whether the detected pulse pair is
ence and provides an output only upon the reception of
Vfalse or true. Referring to FIG. l, a series of ten pulse
an 18 microsecond pulse pair. 'The decoder output is
combinations are illustrated which result in the formation
then employed to start a master time base generator for
of a false 18 microsecond pulse pair. These ten pulse
use within the system. Prior art pulse pair decoders in 45 combinations are the only possible ways in which a false
clude 18 microsecond delay lines which detect the pres
pulse pair can be formed from clashes between DME
ence of a data-link pulse pair among the many pulses
and data-link pulse pairs. The pulse combination illus
received. A disadvantage of these decoders is that it is
trated by curve A demonstrates how the trailing pulse of
possible that a pair of pulses spaced 18 microseconds may
a DME pulse pair and the leading pulse of a data-link
be received and decoded, and yet not he a true data-link
pulse pair may occur at an 18 microsecond time lspacing
pulse pair. The occurrence and characteristics of these
and appear as a false data-link pulse pair. Curve B illus
false pulse pairs will be discussed further hereinbelow as
trates how the leading pulse of a DME pulse pair and
the discussion of the improved decoder of this invention is
a leading pulse of a data link pulse pair may appear as a
developed.
false
data-link pulse pair. Likewise, curves C and D illus
55
One object of the present invention is to provide an im
trate the two remaining Ways in which DME and data-link
proved decoder forV decoding a given pair of pulses.
pulses could combine to produce a false data-link pulse
Another object of the present invention is to provide
pair. Curves E, F, G, H, I and- J illustrate the possible
.a decoder for decoding a given pair of pulses overcom
ways in which two DME pulse pairs could combine to
ling the above indicated false decoding problem.
produce a false data-link pulse pair. The numerals ap
Still another object of the present invention is to pro 60
pearing on the pulses denote whether they are the first
vide a decoder for decoding a given pair of pulses pro
or second DME pulse pair. Itis to be noted that curves
ducing a control signal to prevent a false decoder output.
>E and l, F and I, and G and H illustrate the same physi
VA feature of the present invention is a decoder for
cal pulse spacing and differ only in time of occurrence
generating an output signal upon occurrence of a given
pair of pulses spaced a predetermined time interval com 65 of the respective DME pulse pairs which forrn the false
Vpulse pair combination.
prising a source of a plurality of time spaced pulses
where the plurality of pulses include the given pair of
‘If the ten possible pulse combinations illustrated by
pulses and other time spaced pulses, certain ones of which
may be spaced said predetermined time interval, means
to detect a pair of pulses spaced said predetermined time
curves A to I lare considered, a rule may Ibe formulated
_which can )be stated thus: if there is a pulse present 12
vmicroseconds before or l2 or 18 microseconds «after the
interval, means to detect whether the detected pair of
.second pulse of the 18 microsecond pulse Vpair concurrent
3,051,928
3
4
with the occurrence of a pulse 6 or 30 microseconds be
10 which may be in the form of »a ñip-ñop circuit to pro
fore the said second puise, or when there is a pulse pres
ent 36 microseconds before the said second pulse concur
duce a control signal to prevent the false pulse pair of
curve A, FIG. l, -at taps 5e and 5k from producing an
output from “not-and’ gate 4. Thus, lthe master time
base generator 6 is not falsely started.
rent lwith the occurrence of a pulse either 12 microseconds
before or 12 microseconds after said second pulse, then
the 18 microsecond pulse pair is not a true data-link
Similarly if a false pulse pair of the type illustrated by
pulse pair and the «decoder should be prevented liìrom
producing an output signal.
curve B is received, when the false pulse pair appears at
taps 5e and 5k, a pulse 6 microseconds occurring before
Referring to FIG. 2 there is illustrated an embodiment
of the decoder of this invention which will overcome the
the trailing pulse of the false pulse pair will :appear at
problem of false decoding. In the broadest sense, the
decoder will generate an output signal upon occurrence
of a given pair of pulses spaced a predetermined time in
false pulse will appear at tap 5a at the same instant of
tap 5g and a pulse 18 microseconds after the second
time. The pulse from tap 5g will be applied to “or” gate
7 producing an output therefrom which will be applied
terval and comprises a source of a plurality of time spaced
to “and” gate 8. The pulse from tap 5a will be `applied
pulses 1, said plurality of pulses including said given pair 15 to “and” gate 8 simultaneously with the pulse from “or”
of pulses and other time space pulses, certain ones of
gate 7 causing an output signal from “and” gate 8 which
which may be spaced said predetermined time interval,
is applied to “or” gate 9. The output from “or” gate 9
means 2 to detect a pair of pulses spaced said predeter
will trigger control signal generator 10 which in turn will
mined time interval, means 3 to detect Whether the de
prevent an output signal from “notaand” gate y4 and the
tected pair of pulses is said given pair of pulses, and means 20 master time base generator 6 will not start.
4 to produce an output signal when the ydetected pair of
'If the combination of pulses illustrated by curve C,
pulses is said given pair of pulses.
FIG. l are considered, the false pulse pair will -again
More specifically the `decoder illustrated in =`FIG. 2 is
occur simultaneously at taps 5e and 5k. At the same in
designed to include logic circuitry which operates in lac
stant of time la pulse 12 microseconds before the trailing
cordance ywith the aforesaid rule to produce a control 25 pulse of the false pulse pair will appear at tap 5i and a
signal to prevent :an output upon the occurrence of `a
pulse occurring 36 microseconds before said trailing pulse
false pulse pair. Source of signals 1 represents a source
of a plurality of time spaced signals which may be re
ceived by the TACAN receiver used by the TA'CAN data
link. The plurality of signals may include data-link 30
will appear at tap 5p. The pulse pair occurring at taps Se
and 5k will again tend to trigger gate 4, however, the
pulse pairs, DME interrogating pulse pairs, or random
pu-lse lfrom 5i will cause an output from “or” gate 11,
and that output will be applied to “and” gate 12. The
pulse from tap 5p will cause an output from “or” gate 13
combinations of the two. The signals are fed to a delay
which will also be applied to “an ” gate 12 producing an
line 5 including, in sequence from the input end of delay
output therefrom which will be »applied to “or” -gate 9.
“Or” gate 9 will produce an output which will trigger
35 control signal generator 10 and prevent the occurrence of
line 5, delay line portions 5b, 5d, 5f, 5h, 5j, 5L and Sn.
Delay ¿line portions 5b, 5f, 5h, 5j and Sn each have a 6
microsecond delay and delay line portions 5d and 5L each
have a 12 microsecond delay. Output taps 5a, 5c, 5e,
5g, 5i, 5k, 5m and 5p are disposed at the junction of the
delay line portions as indicated. When »a true data-link
pulse pair spaced 18 microseconds is present, each pulse 40
of the pulse pair will `apear simultaneously at delay line
tap 5k and delay line tap 5e, taps 5k and 5e being sepa
rated by the 18 -microsecond delay contributed by delay
line portions 5f, 5h, 5j of 6 microseconds each. The
pulses are coupled directly to inputs 4a and 4b of “not 45
and” gate 4. The action of gate `4 is to produce an out
put due to the simultaneous occurrence of the two pulse
inputs coupled thereto.
The output signal from gate 4
an output signal from “not-and” gate 4 thereby prevent
ing the starting of master time 'base generator 6.
It will be evident to one skilled in the art that by fol
lowing ythe procedure outlined above with respect to
curves A to C, FIG. 1, the remaining possibilities illus
trated Aby curves D to J, FIG. 1, will also cause the de
coder to operate to produce a control signal from genera
tor 10 to prevent -a false output from “not-and” gate 4.
By employing a decoder of the type described herein
above, Ithe problem of a false decoding occurring due to
combinations of data-link pulse pairs and DM-E pulse
pairs or combination of DME pulse pairs forming false
data-link pulse pairs will be overcome, and the accuracy
and reliability of the TACAN data link operation will
is an indication that «a data-link signal is present and is
used to start at least the system master time base genera 50 be improved.
tor 6. If the pulse pair spaced at 18 microseconds is
While I have described above the principles of my in
due to one of the false combinations of pulses illustrated
vention in connection with specific apparatus, it is to be
in curves A to J, FIG. 1, an output signal due to pulses
clearly understood that this description is made only by
appearing at taps 5e and 5k will be produced, however,
way of example and not as a limitation to the scope of
detection means 3 will detect that Ithe pair of pulses is 55 my invention as set forth in the objects thereof yand in
not a true data-link pulse pair and will produce an in
the accompanying claims.
hibitor control signal which is coupled to “not-and” gate
I claim:
4 at inhibiting terminal 4c to prevent an output signal
1. A decoder for generating an output signal upon
from gate 4.
the occurrence of a given pair o-f pulses spaced a pre
vConsider the occurrence of a false pulse pair as illus 60 determined time interval comprising: a source of a plu
trated in curve A, FIG. 2. When the false 18 microsec
rality of differently timed spaced pulse pairs including
ond pulse pair appears at taps 5e and 5k, a puise will oc
-said given pair `of pulses, such that pulse pairs other
cur 30 microseconds before the trailing pulse of the false
than said given pulse pairs may occur spaced said pre
pulse pair land therefore appear at tap 5m at the same
determined time interval; a delay line circuit coupled to
instant of time that the pulses appear at taps 5e and 5k. 65 said source to detect any pair of pulses spaced said pre
Another pulse will occur 18 microseconds after the trail
determined time interval, said delay line comprised of
ing pulse of the false pulse pair and appear at »tap 5a
integral multiple time delay sections; a logic circuit net
at the same time.
All four pulses will appear at their
respective taps at the same instant of time due to the
work means coupled to said source and to a plurality of
said time delay 'sections of said delay line, said logic cir
action of delay line 5. 'Ilhe pulse from tap 5m is applied 70 cuit network means comprised of interconnected “and,”
to “or” gate 7 causing an output therefrom which is ap
plied to “and” gate 8. The pulse from tap 5a is Iapplied
simultaneously to “and" gate 8 thereby producing an out
put from “and” gate `8 which is fed to “or” gate 9. The
“or” gates effective to produce an inhibit signal upon the
occurrence of any pulse pair spaced said predetermined
time interval, other than said given pulse pair; gating
means coupled to said delay line circuit; and means cou
output from “or” gate 9 triggers control signal generator 75 pling said logic circuit network means to said gating
3,051,928
5
means yfor inhibiting said gating means upon the occur
from the input end of said delay line a first delay line
rence of -any pulse pair spaced said predetermined time
interval other than said given pulse pair.
portion having a predetermined value of time delay equal
from the input end of said delay line, a first delay line
portion having a predetermined value of time delay equal
to one third of said predetermined time interval, a second
delay line portion having a value of time `delay equal to
twice said predetermined value, a third delay line portion
having a value of time delay equal to said predetermined
value, a fourth delay line portion having a value of time
delay equal to said predetermined value, a fifth delay line
having Ia value of time delay equal to said predetermined
value, a sixth delay line portion having a value of time de
lay equal to twice said predetermined value and a seventh
delay line portion having a value of time delay equal to
to one third of said predetermined time interval, a second
said predetermined value, ya pair of signal paths coupled
2. A decoder for generating an output signal upon oc
currence of a `given pair of pulses spaced a predetermined
time interval comprising a source of a plurality of time
spaced pulses, said plurality of pulses including said given
pair of pulses and other time spaced pulses, certain ones
of which may Ibe spaced said predetermined time interval,
a delay line coupled tot said source including, in sequence
to the junction of said second and third portions and the
delay -line portion having a value of time delay equal to
junction of said fifth »and sixth portions, respectively, to
twice said predetermined value, a third delay line portion
derive an output signal on each of said paths upon the oc
having a value of time delay equal to said predetermined
currence of a pair of pulses spaced said predetermined
value, a fourth delay line portion having «a value of time
time interval, a “not-an ” gate coupled to said pair of sig
delay equal to said predetermined value, a fifth delay line
nal paths to produce an output signal in response to said
portion having a value of time delay equal to said pre
determined value, a sixth delay line portion having a 20 detected pair of pulses, means to produce a control signal
in the presence of pulses of said plurality of pulses in a
value of time delay equal to twice said predetermined
predetermined time relationship with respect to the pulses
value and a seventh delay line portion having a value of
of said detected pair of pulses including a first “or” gate
time delay equal to said predetermined value, a pair of
coupled to the junction of said first and second portions
signal paths coupled to the junction of said second and
third portions and the junction of said fifth and six-th 25 and the junction of said fourth and fifth portions, a sec
ond “or” gate coupled to the junction of said third and
portions, respectively, to derive an output signal on each
fourth portions and the junction of said sixth and seventh
of sa-id paths upon the occurrence of Ia pair of pulses
portions, a third “or” gate coupled to the junction of said
spaced said predetermined time interval, a “not-and” gate
third and fourth portions, the junction of the sixth ‘and
coupled to said pair of signal paths to produce an output
seventh portions and the end of said seventh portions re
signal in response to said detected pair of pulses, means
moved from said last-mentioned junction, a first “and”
coupled to said delay line to produce »a control signal in
gate coupled to said source and the output of said second
the presence of pulses of said plurality of pulses in a pre
_“or” gate, a -second “and” gate coupled to the outputs of
deter-mined time relationship with respect to the pulses of
said first and third “or” gates, la fourth “or” gate coupled
said `detected pair of pulses, and means to connect the
output of said control signal producing means to said 35 to the outputs of said first and second “and” gates, means
coupled to the output of said fourth “or” gate responsive
“not-and” gate to prevent the production of said output
to Signal output therefrom to generate a control signal,
signal therefrom in the presence of said control signal.
and means to connect the output of Said control signal
3. A decoder for generating an output signal upon oc
generator means to said “not-and” gate to prevent the
currence of a given pair of pulses spaced a predetermined
production of said output signal therefrom in the presence
time interval comprising a source of a plurality of time
of said control signal.
spaced pulses, said plurality of pulses including said given
5. A decoder for generating an output signal upon
pair of pulses and other time spaced pulses, certain ones
occurrences of a given pair of pulses spaced a predeter
of which may be spaced said predetermined time interval,
a delay line coupled to said source including a plurality
mined «time interval comprising -a source of a plurality of
of output taps spaced therealong a-t given time intervals, 45 time spaced pulses, said plurality of pulses including said
given pair of pulses and other time spaced pulses, certain
a pair of signal paths coupled to a first selected two of said
ones of which may be spaced said .predetermined time
taps spaced said predetermined time interval to derive
an output signal on each of said paths upon the -detection
interval, :a delay line coupled to said source, -a plurality
of output taps «spaced :along said :delay line including in
of `a pair of pulses spaced said predetermined time in
terval, means coupled to said pair of signal paths to pro 50 sequence an output tap spaced .a given distance from the
input of said delay line to provide a v'alue of time delay
duce an output signal in response to said detected pair of
equal .to one-third said predetermined time interval, a
pulses, means to produce a control signal in the presence
second «output tap spaced from said first output tap a dis
of pulses of said plurality of pulses in a predetermined
tance equal to twice said given distance, a third output
time relationship with respect to the pulses of said de
tected pair of pulses including `a first “or” gate coupled 55 tap spaced from said second output tap a distance equal
to said given distance, a fourth output tap spaced from
to a second selected two of said taps, a second “or” gate
said third output tap a Idistance equal to said given dis
coupled to a third selected two of said taps, a third “or”
France, la fifth out-put tap spaced from said fourth output
gate coupled to -a selected three of said taps, a first “and”
tapa distance equal to said given distance, a sixth output
gate coupled to said source and the output of said second
“or’” gate, a second “and” gate coupled to the outputs of 60 tap spaced from said fifth output tap, a distance equal
to twice said given distance and a seventh output tap
said first and third “or” gates, a fourth “or” -gate coupled
spaced from said sixth output tap a distance equal to
to the output-s of said first and second “and” gates, means
sai-d given distance, a pair of signal paths coupled to said
coupled to the output of said fourth “or” gate respon
second output tap and said ñfth output tap, respectively,
sive to signal out-put therefrom to generate a control sig
nal, and means to connect the output of said control sig 65 to 'derive an output :signal on each of said paths upon
the occurrence of a pair of pulses spaced said predeter
nal generator means to said output signal producing
mined time interval, a “not-and” gate coupledv to said
means to prevent the production of said output signal
pair of signal paths to produce an output signal in re
therefrom in the presence of said control signal.
spense to said detected pair of pulses, means to produce
4. A decoder ‘for generating an output signal upon oc
currence of a given pair of pulses spaced a predetermined 70 a control signal in the presence of pulses of said plurality
of pulses in a predetermined time relationship with respect
time interval comprising a source of a plurality of time
to the pulses of said detected pair of pulses including a
spaced pulses, said plurality of pulses including said given
first “or” gate coupled to said first and fourth taps, a
pair of pulses and other time spaced pulses, certain ones
second “or” gate coupled 'to said third and sixth tap, a
of which may be spaced said predetermined time interval,
a delay line coupled to said source including in sequence 75 third “or” gate coupled to said third, sixth and seventh
3,051,928
7
8
taps, a first “and” gate coupled yto said source and the out
delay line portion and said sixth delay line portion, a sev
put of said second “or” gate, a second “and” gate coupled
to the outputs of said first and third “or” gates, a fourth
“or” gate coupled to the `outputs yof said first and second
“and” gates, means coupled .to the output of said fourth
“or” gate responsive to signal output .therefrom to gen
enth output tap disposed between said sixth delay line
portion and said seventh delay line portion and an eighth
«output tap disposed at the end of said seventh delay line
portion, a pair of signal paths coupled to said third output
erate a control signal, and means to connect the output
of said control signal generator, means to said “not-and”
gate to prevent the production of said output signal in
the presence of said control signal.
6. A decoder for generating an output signal upon oc
currences of a given pair of pulses spaced an 18 micro
second »time interval comprising a source of a plurality
of time spaced pulses, said plurality of pulses including
tap land said sixth output tap, respectively, to derive an
«output sign-al on each of said paths upon occurrence of a
pair of pulses spaced said 18 microsecond time interval,
a “not-and” gate coupled to said pair of signal paths to
produce an output signal in response to said detected pair
of pulses, means to produce a control signal in the pres
ence of pulses of said plurality of pulses in a predeter
mined time relationship `with respect to the pulses of said
detected pair of pulses including .a íirst “or” gate coupled
said given pair of pulses and other pulses, cer-tain ones
to said second «and fifth taps, a second “or” gate coupled
of which may be spaced said 18 microsecond time inter
to said fourth and seventh taps, a third “or” gate coupled
val, a 'delay line coupled to said source including in se
to sai-d fourth, seventh and eighth taps, a first “and” gate
quence from the input end of said delay line a first delay
coupled to said first tap and the output of said second “or”
line portion having a 6 microsecond delay, a second delay
gate, a second “land” gate coupled to the output of said
line portion having a 12 microsecond delay, a third del-ay 20 ñrst and third “or” gates, :a fourth “or” gate coupled
line portion having a 6 microsecond delay, a fourth delay
to the outputs of said first and second “and” gates, means
line portion having a 6 microsecond delay, a `fifth delay
coupled .to the output of said fourth “or” gate in response
line portion having la 6 microsecond delay, a sixth delay
to signal output therefrom to generate a control signal,
line portion having a 12 microsecond delay and a seventh
and means to connect the output of said control signal
delay line portion having a 6 microsecond delay, a first 25 generator means to said “not-and” gate to prevent the
output tap disposed between said source and said first
production of said output signal therefrom in the presence
of said control signal.
delay line portion, a second output tap disposed between
said source and said first `delay line portion, .a second out
References Cited in the ñle of this patent
put Itap `disposed «between said first del-ay line portion
and said second delay line portion, la third output tap 30
UNITED STATES PATENTS
disposed Ibetween said second delay line portion and said
third delay line portion, a fourth output tap disposed
between said third delay line portion and said fourth
delay line portion, a fifth output tap disposed between
said fourth delay line portion and said ñ-f-t-h delay line
portion, a sixth output tap disposed between said ñfth
2,522,609
Gloess _____________ __ Sept. 19, 1950
2,641,698
2,706,810
2,779,933
2,800,584
Gloess ______________ __ June 9,
Jacobsen ___________ __ Apr. 19,
Bradburd ___________ __ Jan. 29,
Blake ______________ __ July 23,
2,884,615
Garñnkel ____________ __ Apr. 28, 1959
1953
1955
1957
1957
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