HP 415E User Manual

Section HI
Paragraphs 3-25 to 3-32
3-25.
LOW
SWR,
Standing
wave
ratio
between
1.0
and
1.24
canbe
read
quiteaccurately
onthe
EXPAND
scales
of
the
meter
when
the
EXPAND
switch
is
set
to
any
position
other
than
NORM.
3-26.
MODERATE
SWR,
HIGH
RESOLUTION.
The
EXPAND
and
-DB
scale
can
be
used
together
with
the
EXPAND
switch
to
read
any
SWR
with
high
resolution
in
DB.
Figure
3-5
and
3-6
are
used
to
convert
DB
to
SWR.
The
reference
level
(full
scale
meter
deflection
ata
voltage
maximum)
can
be
used
with
the
EXPAND
switch
at
NORM
(since
0
db
NORM
and
0
db
EXPAND
correspond)butgreater
accuracy
is
obtained
by
setting
the
reference
level
with
the
EXPAND
switch
to
0.
30
20
STANDING WAVE RATIO
o
о 4 8 12 6 20 24 28
DECIBELS (SWR)
415E-A-2
Figure
3-6.
Converting
Decibels
to
SWR
3-27.
HIGH
SWR.
High
standing
wave
ratios(greater
than
30,
or
sometimes
10)
present
problems
because
of
excessive
probe
penetration
(to
lift
the
minimum
above
the
noise
level)
and
departure
of
detector
behaviour
from
square-law.
Both
problems
are
lessened
or
elim-
inated
by
measuring
only
the
standing
wave
pattern
near
the
voltage
minimum,
where
probe
loading
effects
are
least
disturbing.
3-28.
TWICE-
MINIMUM
POWER
METHOD.
The
basis
for
this
method
(andthe
TEN-TIMES-MINIMUM
POWER
METHOD)
is
the
fact that
for
a
high
SWR,
the
standing
wave
pattern
approximates
a
parabola
in
the
vicinity
of
avoltage
minimum.
The
slotted
line
carriage
must
have
a
good
scale
or
dial
indicator.
Measure
the
distance
(AX)
between
positions
on
the
standing
wave
pattern
where
the
voltage
is
3
db
above
the
voltage
at
the
min-
imum.
Alsomeasure
the
transmission
line
wavelength
^g
(standing
wave
pattern
minima
are
one-half
wave-
length
apart
and
the
sharp
minima
resulting
from
3-6
Model 415E
short-
circuiting
the
transmission
line
are
easy
to
lo-
cate
accurately).
Compute
the
SWR
from
the
following
formula:
swa = Ул Sx).
3-29.
TEN
-ТІМЕЅ-
MINIMUM
POWER
METHOD.
Ап-
other
convenient
"level
above
minimum
method"
to
use
for
computing
SWR
is
alevel
10
db
above
minimum,
The
separation
(A X)
between
these
positions
Should
be
put
in
the
following
formula:
3,
(А
SWR=
Ут
(
gax)
For
standing
wave
ratios
as
low
as
15
(о
1,
the
accuracy
of
this
method
is
within
1%.
3-30.
SWR
MEASUREMENT-SOURCES
OF
ERROR.
Several
possibilities
have
already
been
mentioned:
excessive
frequency
modulation
of
source
(smears
out
sharp,
deep
nulls
of
high
SWR
pattern),
harmonics
of
signal
frequency
from
source,
departure
of
detector
from
square-law
behaviour,
and
excessive
probe
pen-
etration.
Also,
reflections
in
the
transmission
line
between
the
slotted
line
and
device
being
measured
must
be
minimized.
3-31.
ATTENUATION
MEASUREMENT.
3-32.
The
415E
may
be
used
for
high
resolution
in-
sertion
loss
measurements
simply
by
inserting
the
device
to
be
measured
between
signal
source
and
de-
tector
and
noting
the
change
in
DB
indication
on
the
415E.
A
typical
measurement
is
shown
in
Figure
3-7.
The
continuous
coverage
of
the
EXPANDscales
allows
any
attenuation
measurement
to
be
made
on
the
EX-
PAND
scales.
For
accurate
results,
both
the
signal
source
and
the
detector
should
be
well
matched.
Im-
pedance
match
of
source
and
detector
can
beimproved,
if
necessary,
with
padding
attenuators,
isolators,
ОГ
tuners,
dj MODEL 415Е
SIGNAL
SOURCE
о
IMPEDANCE MATCH
HERE
ATTENUATOR
Figure
3-7.
Attenuation
Measurement
Setup
02152-2

HP 415E Specifications

General

Brand	HP
Model	415E
Category	Measuring Instruments
Language	English