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Pigure'
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For'faste~
leveled swept frequency rates,
l~~gative
, output detector-and directional couplercombina-
tions
such
'as .the HP Model 7'86D
and
78·7D Direc-
. tional
Detectors
can
be
used insteadof
the
power
.:
meter'
and ,"thermistor
mount
combination
.de-,
scribedabove.'Typically,'
for
the
directional detec-
,
'.,i'
tor
and. leveler campJifier combination, leveled
,
loop
equip~nen(should
be selected.
onthebasis
of. ' power can be
held
constant
within ±0.2'idB (plus
.main "line
R.F·
power. .levels and' leveling: .require-
fr~quency
'.'
response
hf
directional detector).
ments.
III
the closed-loop system. shown in-Figure 9 Note:I the,'
f~quency
response
of
the
directional
:the".~atnes~o..~
lev~1iIlg'i3
deteririi'n~d
primarily by
detector
includes coupling
;:variation,a~d,
RF
re-
,,'.:' the,',co.\1plirig' variation
of
the
directional coupler spouse
of
the
crystal.
For
the
~~~~Jel
7,'86D
(0.96.
,,"
:used. l'he
powermeteris
usetr,Q'ecause
it
provides
to
2.11 GHz)
this
,is
I±O,;2"dB.
,,'
".
i ,
extra
190P gain. In' addition,
with
output
coupling
,'l(nQwl\;"'t,he' main
line'.output.power
can
be read
directly
on
the
powermeter allowing
for
coupling'
AMP~ITUDE
MO'DULATI'ON .
'variation.
The
'leveler
~pIU~.er
used
has
a, 0 to,
'The
PIN' Modulator can be, used
to
amplit~de-'
-27,
Vdc
output..c~p~l,)i1ity
WIth
output
impedance modulate
the
RF' signal with
.almost
any
'time-
.""
of
about
20
'kn,
hence'
the
20
k,Q
"series resistor 'varYing signal. Modulation
'~~accompl,ished
with
a"
•
::'"
'i,
makes it 'a
biascurrentsource
providing a
'maxi-dcblas'
'current.
to
obtain
a, specific attenuation
mum, L3S'
rnA'
decurrent
(referring
to
~igltr.e
4,
"1'
"level and
thensuperimposi~ga
.time varying cur-
.-
'.
this means
tha,t'the
maximum control range
po~:
.'
rent upon the bias current,
Th~
specific
attenua~
"
'.
,sible
using 'an'
"A"
model
8730
is' between
l~'and
tion
level
~.tpon~"which
the
'modulating
signal
is
.
..
",
20 dB depending
upon
the
individualB'[Sf) used).. '.
"sllperHnp6$~d'
must
be equal
to
or
'greater..
than
the
Typically, with
the
power
meter
and
leveler
ampli-'
peak
amplitude
of
the,
modulating signal,
or
peak
fier combination,
leveled
power
can be, held con-, ' 'clipping will
QC,<;\1r
."A
'¢ontroi
instrument
designed:
stant with ±0.2 dB,(plus coupler variation) for R'F
fQr,
I
use
'.
'tn
modulating
applications with
~he
PH~"
swept 'frequency rates
equal
to
orlonger
.than
30'
Modulators is
the'
HP Model
8403A
M,odulator
',seconds/o,ctave.
'In
practice, slowest swept' fre- which provides'
frequency
compensation'
for
ex-
..
.'
;'.
tending ·the.PIN Modulator AM frequency response .
. )
':':",
tolD
MHz. However, a typical
setup
for modula- '
J; , , ting applications, without. the use
or
the
HJi'
Model'
~1*P3A
Modulator.Isillustrated in Figure
10.'
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