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HP 416A - Method of Operation

HP 416A
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A
coaxia
l
-to-waveguide
adapter
to
connect
the
sign
al
s ou.1
·c
e
to
the
wa
ve
-
guide,
such
as
a
Hewlett-Packard
Model
281A
Waveguide
to
C
oaxial"
Adapter
.
..
A
waveguide
attenuator.
This
equipment
is
optiona
i,
but
.for
maximum
ac
-
curacy
an
external
attenuator
is
recommended.
Waveguide
attenuators
such
as
the
Hewlett-P
a
ckard
Model
X382A
Broadband
Precision
Waveguide
At-
tenuato
r,
l\
1odel
37
0
Fixed
Wav
e
guide
Attenuator,
or
Model
375
Waveguide
Variab
le
Flap
.Atten
uator
are
suitab
le
.
A
d-c
oscilloscope
with
a
long-persistence
screen
·
optional).
lv1ethod
of
Operation
- In a
reflectometer
system,
a rn
ic
rowave
oscillator
delivers
to
a
transmission
system
terminated
in
an
unknown
l
oad
a
signal
modu-
lated
by
a
1-kc
square-wa
ve
voltage.
By
means
of
the
two
d
irec
tional
couplers
in
the
transmission
systern
,
bet
w
een
the
source
and
th
e
load
, t
he
i
ncident
and
re-
flected
powers
are
samp
l
ed,
and
each
is
subsequently
dete
cted
by
a
squar
e
-law
crystal
detector,
the
output
from
which
is
transm
it
ted
to
the
Model
416A
Ratio
Meter.
Thus
t\vo
1-k
c v o l
tages
,
on
e p
ropor
ti
ona
l
to
th
e
incident
p o
wer
and
t
he
other
to
the
reflected
pow
er
,
are
deli
ve
red
to
the
Mode
l 4 1
6A
wh
er
e
th
e
voltages
are
combined,
their
ratio
indicated
on
the
meter,
and
a
d-c
volt
age
proportional
to
the
magnitude
of
their
ratio
made
available
for
applica
t ion to a n
osci
llo
scope
.
Advantages
-
In
the
measurem.ent
of
reflection
coefficients,
the
reflectom.-
eter
has
several
advantages:
Range:
Reflection
coefficients
may
be
meas
u r e d n
ot
on
l
y·
a t a
sing
le
frequency
or
over
a
narrow
band
,
but
ov
er
a
wi
de
ba.nd
of
swept
frequencies.
Speed:
Over
a
band
of
swept
frequencies
as
we
ll
as
at
s
in
g
fo
frequ
en-
cies,
visual
indication
of
reflection
coefficient
i s
give
n
a.lrnost
instantly.
Accuracy:
Under
comparable
conditions,
the
reflectomet
er
i s a s
ac-
curate
or
more
accurate
than
the
usua
l
me
di
u
rn
for
s
uch
rnea
s -
urements,
the
slotted
line.
The
calibr
a
tion
feature
of
the
Model
416A
makes
it
possible
to
over
come
s
orne
of
t
he
ina
ccuracy
inherent
in
any
microwave
m.easur
en1e
nt
s
etup.
Me
asurement
of
low
reflection
coefficients
{difficu
l t
to
m
ea
s u
re
under
usual
methods)
can
be
rnade
wi
th
great
a
ccu
racy
at
sing
le
frequencies
by
the
use
of
additional
equipn1ent
{a
slide
s c
re
w tune r
and
sliding
load).
Visual
Plot:
The
a v a
il
ability
of
a d
-c
voltage
pr
oportio
n
al
to
the
'magni-~
tude
of
the
reflection
coefficient
,
fo
r
:ipplication
to
an
osc
illoscope
,
makes
possible
an
accurate
plot
of
re
flectio
n
coefficient
versus
frequency
when
voltage
of
t
he
proper
fre
que
n
cy
is
ap
plied
to
the
horizontal
pla
tes
of
the
oscill
oscope
. (A
si
gna
l s ou
rce
such
as
the
Model
670HM
provides
a
source
of
s u
it
ab le
ho
ri
zonta
l
swe
e p
voltage.)
The
speed
with
which
a
visua
l p
re
sentat
i
on
of
refl~ct
i
on
-10"'

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