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HP 416A - Page 45

HP 416A
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Most
of
the
more
important
errors
resulting
from
various
factors
general-
ly
will
be
apparent
when
calibrating
and,
as
seen
on
an
oscilloscope,
will
appear
either
as
ripple
or
curvatureo
ao
Ripple
may
result
from:
(I)
Small
residual
spurious
signals
which
combine
in
random
phase
relations
0
Generally
the
fact
or
which
is
the
greatest
contributor
of
spurious
signals
is
mismatch
between
the
detectors
and
the
tra
nsmission
system
0
(
2)
In
broadband
operation,
variations
with
frequency
of
the
RF
power
input
to t
he
detectorso
b.
Curva
tu
re
may
result
from:
(I)
Lack
of
tracki
ng
between
the
power=in/voltage-out
characteristic
'
of
the
two
de
tect
ors,
if
ope
rating
outs
i
de
the
linear
region
of
the
det
ector
square-law
characteristic
0
(2)
La.ck
of
trackin
g
between
difference
with
frequency
in
rectification
efficiency
(in
db)
of
the
two
detec
t
ors
.
(3)
Lack
of
tracking
between
the
differences
in
coupling
characteristics
(in
db)
of
the
two
couplers.
In
the
following
paragraphs.
factors
which
may
contribute
to
error
are
discussed
briefly
o
NOTE
:
For
a
more
comprehensive
discussion
of
these
factors,
see
the
Hewlett
=
Packard
Journal
(Vol.
6,
No
.
1-2)
Possible
Errors
if
Input
Power
to
Detector
Too
High
-=
Square
-
Law
Characteristics
=
For
operation
in
the
X
band
,
presently
available
detectors
(Model
X421A
Waveguide
Crystal
Detector
Mounts)
are
crystal
diodes
equipped
with
matched
resistive
loads
.
When
the
Model
X4Z
lA
is
operated
at
an
input
power
of
0
dbm
or
less
,
the
relation
of
input
rf
power
to
output
audio
voltage
follows
a
linear
characte
ristic
,
as
in
dicated
in
Fig
.
8-L
If
,
however
,
when
calibrating(generally
performed
under
a
condition
of
100%
reflection)
,
the
level
of
the
input
to
the
detectors
is
above
that
at
which
there
is
a
square-law
relation
between
the
output
voltage
and
the
rf
voltage
atthe
input
to
the
detector,
an
error
will
be
introduced
i
nto
the
measurement.
The
error
introduced
into
a
measurement
because
of
detector
variati
on
from
square
=
law
is
a
function
of
the
power
level
applied
to
the
detector
when
the
system
is
calibrated.
This
relation
between
magnitude
of
error
and
level
at
which
calibration
was
performed
is
indicated
in
Fig
.
11-1.
Operating
Cons
i
derations
=
Operating
the
incident
detector
within
the
linear
region
of
the
crysta
iu
s
input
-
output
characteristic
generally
is
possible
because
even
in
broadband
operation
the
dynamic
range
over
which
the
incident
detector
=3 0 -

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