3
dB
Linearity
Check
Use
the
3
dB
linearit y
c
hec
k
k
ey
on
the
RF
preselector
to
c
hec
k
for
o
v
erload.
Press
the
3
dB
LIN
k
ey
and
observ
e
the
amplitude
lev
el
of
the
signals
display
ed
on
the
sp ectrum
analyzer.
The
c
hange
in
the
observ
ed
p eak
lev
el
of
signals
(at
least
10
dB
ab o
v
e
the
noise
o or)
should
b e
less
than
1
dB.
If
c
hange
in
amplitude
o ccurs,
increase
the
RF
preselector
input
attenuation
b
y
10
dB
and
rep eat
the
3
dB
test.
Con
tinue
to
add
attenuation
un
til
the
signals
b eha
v
e
linearly
.
Use
the
least
amoun
t
of
attenuation
necessary
to
cause
linear
signal-amplitude
c
hange.
Narro
wband/Broadband
Signals
The
classication
of
a
signal
as
narrowband
or
broadband
dep ends
on
the
signal's
o ccupied
frequency
sp ectrum
relativ
e
to
the
resolution
bandwidth
of
the
measuring
receiv
er.
Narro
wband
Signals
Emissions
o ccup
ying
a
narrow
frequency
sp ectrum
relativ
e
to
the
resolution
bandwidth
are
dened
as
narrowband.
A
CW
signal
is
an
example
of
a
narrowband
signal.
See
Figure
4-2.
Common
measuremen
t
units
for
narrowband
signals
are
dBV
(dB
ab o
v
e
1
V)
and
dBV/m
(eld
strength).
Figure
4-2.
Narro
wband
Spectrum
4-2
Making
Typical
Measurements
HP
8572A
EMI
Receiv
er
User's
Guide
