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r' cover story. ~
Simplify Your Amplifier
and Mixer Testing
New Network Analyzer Has Nonlinear Measurement Capability.
8y Jim Curran
Hewlett-Packard Co.
When measuring a device's linear and
nonlinear characteristics, multiple test
configurations are typically required. Net-
work analyzers have traditionally been
used to measure the linear reflection and
transmission characteristics of RF com-
ponents, such as filters and cables, byap-
plying a known swept signal and then
measuring the magnitude and phase of
the transmitted and reflected signals. Ac-
tive devices such as amplifiers and
mixers, however, require both linear and
nonlinear characterization. Each device
must be moved between one test set-up The HP 87538 offers new features for nonlinear measurements and direct control of
to measure impedance, amplifier gain external instruments.
and mixer conversion loss and another
loss is added to the contributions of its
set-up to measure harmonics and inter-
modulation distortion. The latest RF net-
work analyzer from Hewlett-Packard Co.,
predecessor, the HP 8753A. In addition,
the HP 87538 offers other new features
A device's behavior is linear when a
sine wave input produces a sine wave
output at the same frequency with only an
the HP 87538, dramatically simplifies and designed to aid manufacturing test ap- amplitude and phase change. Examples
speeds these tests. The ability to measure plications and provides frequency cover- of linear devices are filters and cables.
amplifier harmonics and mixer conversion age from 300 kHz to 6 GHz. The output of a nonlinear device is de-
.-------- --- ----------- ---- ------------ - ---..,,,
, j------------------------------------------' pendent on the power level of the input
,
,
,
,
,
,
,
signal and is usually composed of multi-
, ,
: RF Sowc. : Frequency RF Sowce ple signal components at harmonically-
: : RF
1 ~ RF
related frequencies. Examples of such
! ~~
Output ,. 100 MHz
: : ,__ U" Q
: 1104Hz
'Reference~ devices are saturated amplifiers and
N=2
300kHz to
mixers.
J GHz Figure 1a contains a block diagram
which illustrates how the HP 87538 is nor-
mally configured to make linear measure-
1--'----\ X _l:_A X
ments. The RF source stimulates the
: : =
IF IF _,:,,_A
filtering,
IF=lMHz IF "'.5 MHz amplifier under test (100 MHz in this ex-
lit......
: N= 2 :
-'"'
lklcIef ample). The incident and test signals are
detection
iLO:99M1'~ Too' : lO=99.5~ Test
received and mixed down to a low fre-
, j~
d1~., ~=i':Hz ~~,m'=200MH' quency IF (1 MHz). The 1 MHz IF signal
--
OOJ
-,
i
is filtered to remove unwanted signals and
then measured. The 1 MHz IF signal in
, ==.= ~:"1
N='
LO= 'l99t.ttz the Reference (R) channel also goes to
rv xN i one input of a phase detector. The other
JO-EO 104Hz Humor*:
Generator
:
i input is fed by a stable 1 MHz frequency