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POWER
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A~~LITtJ)DE. '~1ODUb,~r.I()N:'\t)M9~EL6!5IB
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9.
'.,Typical Clqsed L~)'op t~veling S;istem',
.,' Figutlj"l O)Typical ,Genera/Modulation ~etup
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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-
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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
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response
hf
directional detector).
ments.
III
the
closed-loop system. shown in-Figure 9
Note :
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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-
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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. ,,'
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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"
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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-
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' . this meanstha,t'the maximum control range
po~:
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rent upon the bias current,
Th~
specific
attenua~
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,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- . .
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tending ·the. PIN Modulator AM frequency response .
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tolD MHz. However, a typical setup for modula- '
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ting applications,
without. the
use or
the HJi'
Model'
~1*P3A
Modulator.Isillustrated in Figure 1 0 . '
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