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reference channel, the amplitude
of the standing-wave max
voltage is made
equal to that of the reference voltage.
And therefore the
max-to-min standing-
wave ratio may be obtained by comparing
the standing-wave
min
voltage
to the
reference voltage.
With the circuit
maintained
as set up by the calibration
procedure, the standing-wave min
voltage will
undergo the same degree of
loss or gain as the standing-wave
max voltage, and
therefore a condition of
true ratio is maintained.
To obtain the standing-wave min
volt?-ge,
the probe in the slotted line
is moved along the line until the point of standing-wave minimum amplitude
is found.
With the probe at the node,
the indica.tion
given on the Model 416A
meter is the ratio of the standing-wave
maximum (
11
l11
by virtue of the cali-
bration) to the standing-wave minimum (node
voltage
in the Model 416A probe
channel).
For instance, if, with
the
probe at
the
standing-wave node, the
voltage in the probe channel is
O.
2
volt, the Model 416A (on the SWR scale)
will indicate 5, which is the ratio of
NOTE:
1
{voltage proportional to
standing1
-wave max)
O.
2
(voltage proportional
to
standing-wave min)
When the ratio meter
is
used
in
a slotted-line system, the
indication on the PERCENT REF.I,,ECTION (REFLECTOM-
E TER) scale is
irreleva
nt, does
not
indicate the reflection
coefficient of the load under measurement, and cannot be
used to calculate the standing-wave ratio from the formula
1
+
IP
I
1
-
IP
1 •
There
is no connection between
the indications on
the PERCENT REFLECTION and SWR scales as each is
calibrated for use only in its particular type of system.
-hp·
X421A
WAVEGUIDE
CRYSTAL DETECTOR
-hp-
416A
RATIO
METER
MOUNT
'--..,~~~~--~~~~
-hp-444A
BROADBAND
PROBE,UNTUNED
-hp-
X281A
WAVEGUIDE·
TO-COAX.
ADAPTER
·
hp-
809B CARRIAGE
-hp
·
xa10
B
SLOTTED
SECTION
-hp-
620 A
SHF
SIGNAL
GENER ATOR
'x'
Fig. 16.
Typical Slotted Line System
Model 416A Used as
SWR Indicator
Block Diagram
-40-
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