Allied Radio Knight KG-640 운영자 매뉴얼 - 페이지 11

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HOW
TO MEASURE
DB (Decibles)
AC output voltages are often measured in units called Decibels,
which are used to indicate power levels in amplifiers or general
telephone work. The DB
scale
(bottom
meter
scale)
is based
on the voltage developed across a 600 ohm line when .001 watt
is dissipated.
This
voltage
is assigned
the
reference
0 db.
Such a voltage deflects the pointer to .775 volts on the 0-2 volt
AC range. Therefore, a direct meter reading in terms of deci-
bels can be made
only when
the meter
is connected
across
a
600-ohm
resistive
load. Otherwise
only
relative
db measure-
ments
can be obtained. However,
in a large number
of cases,
relative
measurements
are
appropriate,
since
reference
con-
ditions are defined by other factors and only relative variations
are important.
To measure
DB, proceed as follows:
[] Plug the black test lead
into the jack marked
—COM.
Plug
the
red
test
lead
into
the
jack
marked
OUTPUT.
NOTE:
When
no DC
voltage
is present,
the VOA
jack can
be used since the DC blocking capacitor is not required.
(] Rotate the selector switch to the highest AC range
and
work
down
to one
which
will provide
a reading
at the
right hand side of the scale.
[J The meter pointer will indicate a reading in DB.
AC VOLTAGE
RANGE
21