ln
fact the formula
which
relates
dB. with
watts is
as follows:
Dividing
the
total
dB
by
10
we obtain
the
logarithm
of
the
ratio
between
the
pow.er
output
wl""'*''
of-the"receiver
rni-tnlsiindlio-oie,
*trictr in
the case of
the 680
model
is
I mw.
Once
dB.
:
10
,0,,
#
r
*,il.j,r,}.t
tlflbtr,"T
i,,[
_,Lfi,r"t-_ft1';;il,*,,
H3li,
$..,f;1y..T,1'll'ifl.'J,[fil
ttat.is
ten times.the
logarithm
on a
decimal basis
or the ratio
between
watts
in consideration
-
lrr::lXl#:;:ffi:':#
J:t.iTJ,Xlt'
to be
tested'
(W
l)
and the reference
Watts
(W
0).
is nesative'
measured
on fi,e
-io
'iir[-ouiput
range.
ln the LC.E.
Mod.680R
tester-the
reference
(0
level) marked
on the
scale is,
as already
The K
factor
is calculated
as
follows:
said, represented
by 1 mW
at
600 ohms,
that is the
lnternational
Telephone
Standard
hai
600
been
assumed.
K
-
10xl0g.
-
=
l0xlog.
188.
Normally
however
the load
of
a radio receiver
0r
an amplifier
is
provided
by the moving
3-2
coil..loudspeaker
with
an
_approx.
3
+ 7 ohms, impedance.
Therefor'e
to the
ieading
takei
0n a
logarithmic
table
the
logarithm
of
188 is
2.274
thusz
on the
instrument,
must be
added a certain
factor
represented
by the
letter
K whlch
can
-
10x2.274
-
22.74.
be computed
using
the
following
formula:
600
{
trre totat
dB
wiil therefcre
be;
14
+
22.74
-
36.74.
I
iirioirg
ili" total-dC
ui tO
we
find
the
logarithm
of
the
power
ratio:
36.74
divided
by
K
-
10'
Ioc'
Ioud;;rirtun..
io
=
i.oz+.
read
directlv
on the
scale.
For the
50 volt
range,
add
14
dB
to [he readings.
For
the
-
il;;;;r;ilri
,r.,. output
is
4.72t
mw.
There
is also
a.very
much
simpter
and
quicked
be as follows:
measure
the
output
ioltage
already
describeo,"on
tire
irlmiry-oi
the ou-tput
transformer
.with-
10
vott range
-
dB
reading
f
K. tt-etiiionuary
iilir.o'i,i-ir,,ir-rivi,igioii
ot
ii'.
loudsp'eaker,'alternativelv
on
the terminals
of
50
vott range
-
dB reading
+
K
+
14
dB.
iil
m;vint
coii
"ne?in'i'
ii-riinij
ifi.-irp.dance
valu6
suppbrting
the
measurement
and
then
250voItrange=dBreading+K+28dB.applythefollowingformula:W'
1000
volt
range
=
dB reading
+
K
+
40 dB.
-
Z
92
33
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