
34-11Microwave Measurement
34.3.4 Tracking Preselection
For small input signals, the spectrum analyzer can be considered a linear device. However, if the input
le
vel
in
creases,
ha
rmonics
an
d
IM pr
oducts
ar
e
ge
nerated
du
e
to th
e
no
nlinearities
of a mi
xer
. e
se
pr
oducts
re
sult
in sp
urious
sig
nals
on th
e
sc
reen
of th
e
sp
ectrum
an
alyzer
. In ad
dition,
im
age
fr
equen-
cies
wi
ll
ap
pear
on th
e
sc
reen,
as de
monstrated
ea
rlier
. To av
oid
th
ese
sp
urious
re
sponses,
a tr
acking
pr
eselection
l
ter
is em
ployed
at th
e
in
put
of th
e
sp
ectrum
an
alyzer
. A tr
acking
pr
eselection
l
ter
is an
el
ectronically
t
uned
b
and-pass
lter
u
sually
r
ealized
u
sing
a y
ttrium
i
ron
g ...