4-6
4. Disturbances resulting
from
interrogation signal echoes
are
short-circuited
to
GND.
5.
By
means
of
pulse regeneration the pulses for the decoded
input
receive a
uniform
shape independant
of
the receiver
input
voltage.
The video signal is applied
to
the
suppression
gates
as
long
as
the
signal
is
above the
set
response i:hreshold
and
is
not
an
echo signal. These
gatP.s
havP
the task
of
swit~hing
thP.
rle~orler
OFF under
the
following
criteria :
Mode selector in position
SBY (stand
by)
During a transponder reply (deadtime interval
30-
35J..ts)
DME transmission signal
at
input
Du ring
si
de
lobe interrogation (SLS deadtime interval approx.
35J..ts).
4.2.2 Decoder
Mode A 1 C decoding receives the video signal via the suppression gates. The main task
of
mode A 1 C
decoding
is
to
permit
the transponder
to
reply
on
detection
of
a mode A
or
mode C interrogation. Mode
A
1 C decoding teatures redundant decoder channels,
two
each
of
which
serve
to
decode a mode A inter-
rogation
or
a rr,ode C interrogation. ln addition, the deadtime interval
is
estab!ished in
the
decoder,
it
being approx.
30-
35J..ts.
This deadtime
is
necessary
to
avoid
applying
interrogations
to
the
decoder
whilst
the transponder
is
replying.
Side lobe decoding which
is
also signalled via the suppression gates permits suppression
of
replies
to
side
lobe interrogation.
At
the
same
time
an
SLS deadtime interval
is
formed
and
the
decoder shut
OFF
for
aporox.
35Ms
via
the
suppression gates.
Wh
en
a signal
from
the
decoder
is
established
as
a mode A
or
mode C interrogation,
the
encoder
is
signal led
ON
and
the
reply
Jamp
control
activated
for
the
REPLY
Jamp.
DME
lockout
is
also carried
out
by the decoder. When the decoder produces a reply a voltage pulse
is
simultaneously applied to the instrument connector wh ich
inhibits
a DME transmit signal du ring the
transponder
reply, and
for
the duration
of
a DME
transmit
signal
the
decoder
is
locked
out
via the
same
li
ne, thus preventing a transponder reply.
4.2.3
Encoder
The encoder mainly
has
the
following
tasks :
1.
Capture
and
decode mode A
or
mode C interrogation pulses.
2.
To
generate and propagate reply pulses.
3.
Activate the
transmitter.
The cloc:k generator
is
trigged
by
the decoder and generates the
clock
pulse
(timing
signal)
for
the trans-
ponder
reply in
1he
reply pulse spacing
of
1.451.ls.
This clock pulse
controls
the ring
counter
and activates
Ll1e
mo
du
lator via a
re
ply
pulse shaping circuit and
Jogic
elements. The ring counter
gene
rates the reply
pulses which
are
entered
into
the coding circuit. Coding
is
formed
by
a mode A
reply
by
means
of
the
coding switch
on
the
front
panel
of
the transponder and
by
an
external encoding
altimeter
in a mode C
reply.
The coded response pulses
are
applied
to
the
modulator
input
via the logic elements. The frame
pulses
F1
and F2
are
not
included in coding
of
the
signal
pulses
but
are sent
directly
to
the
modulator
from
the ring
counter
via
the
frame pulse
formation
and the logic elements, the
same
happening
to
the IDE NT
pulse
formation.
On
pressing the
IDENT
button,
the
SPI
pulse
is
applied
to
the rnodulator via logicelements
with
the aid
of
the
!DENT
ti
mer 'for
approx.
30
s.
At
the somc
tirnc
the
rcply
Jomp
control
is
activated
by
the
!DENT
timer.
09/80
<t
0
0
co
co
>
Cl
The document reference is online, please check the correspondence between the online documentation and the printed version.
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