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Figure 13. Dynamic
Bias
Switching
Waveform
..
'.
..":
','
,
,/
" , '
I ~
level with
the
.same PIN Modulator. This can
be'
, accomplished
by
simply
setting
up
a closed loop
leveling
system
~~d
adjusting
the
reference
atten-
uation
level
£0
a
point
equal
to
the
peak
amplitude
of
the
d~sir~d
modulating signal.
For
.this
type
of
.
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,
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..".,
) '.,
MUL
TIPLEFUNCTION"
FQr"
c~rtain
applic;.ations, /it .may be desirable
to
level and amplitude.
modulate
a given RF power
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Page
10
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lor
a/maxinlum
attenuation.
',Once
.'
maximum
at-'.
',; "
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~
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'....
~,'
"
tenuation
.level is established,'
the
RFpowe,r
may
\, .,
'.
.
".
.
..
:be' pulsed
"on"
by applying .aconstant +5
to
,6
.,' '
'::volts'
to
the
"BIAS
input
(voltage'
,ntist'
b~
refer,; , :
".'
e~ce(r>to'PIN,Moduiator
ground).At~the·~~l(i
'o'f", .
. desired pulsewi,d,th,
the
,+5
to
6,
voltdepotential
'
must
beswitchedto.a
-0.8
volt levelwithratedv
.
'.
.
'.
.
.,
I
.bias
current
to
switch
the
RF
off.
' i :
SrGNALSEPARATION
(GATING)
, j • " 'I ,
;'\
Figure
14!
illustrates
u~,
of
the
rI~{
.Modulator as'
...'
an·
RF gating device
for
eliminetlng' spurious or'
" "gh'ost"'signals, in
antenna
range receivers.'
",
'r
,~
.
, .
. '
,>
',i
,'"
i'
,
.t
:'
To"
obtai~"p~lsing
with
rise'and
fall
'time~
in
~h~/
, , ) '.
order
of
15
'to
40
nanoseconds,
the
PIN Modulator
rnust be biased with
the'
HP
'Model
8403A
or
from, :
,",
,;!,,'
,I~
specially shaped' impulse
waveform'
sho~n"
in', '
",F~gure
-13.
However,
if
rise
,and
fall times in
the
, 'I. '
.order
of
100
to
300
nanoseconds
aresatisfactory
,a'
, " \
'setup
such as is shown
in
Figure
10
may be used.
;i:',
~l'Q'te:
in
any
modulating system,'modulating capa-
bility depends upon
the
modulating waveform'
at
the
BIAS
'input
·cQnnectQf. Hence,
lead,
lengths
. 1 . ,
I'
should-be as
short
.aspossibleto
avoid capacitive
,.cable effects. .i. ' .
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..
II,
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,
RECEIVER.
.
PUt'MODULATOR
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2
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,.nu.
::
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DESIRED
:<',)
S'IGN1AL
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RF
,
II"
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PULSED"
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SYNC ' (
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,j,j?igure,14.
Typical'U~eof
PIN
~odu.latpr
as
an'R.-F'"
Gating
Device
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