Table of Contents
Advertisement
;.g. i"
rlz::::;3iiiE!
Example: For
a
Irequency oI
?2
kc,
aet the 0-100 knob
to
?0, the 0-10 knob
to
2 and the
multi-
plier
to
X1000.
Toselect
the
desired output amplitude into a high
impedance
load (10Ke
ormore):
set
the
LoAD
awitch
to internal,
the ATTENUATOR
to
the
nearelt full
scale vatue above the desired outpuq
adjust the OUTPUT control to give the desired output
on
the appropriate
meter
scale.
Example:- Desired voltage ?.3
volts.
Set
ATTENUATOR
to
10
volts
IuIl scale.
Turn
OUTPUT
to give a
?.3
volt
reading on the
O-10
volt
scale.
Example: Desired
vortage .025
volts.
set ATTENUAToR
to
.oB
vorts
rulr scale.
Turn
orrr-
PUT to give a 2.5
volt
reading
on
the
O-B
volt
scale.
To
select.the desired output
amplitude
into
an
external
600
e
load
(1
volt
maximum):
Set the
LOAD switch to external
and
proceed as
above.
USING
THE DB
SCALE
The decibel
is
a
ratio of
two power Ievels
and
is used in
comparative
expressions.
It
may
be
appLied
to voltage levels
iI
the
impedances
are identical.
Itmaybe
used as a quantitative
indic-
ation
for
one power or voltage level
iI
the other
level is defined.
ln this
instrument, the
db
scale
is
based on a relerence
or
standard level o{
0 db = 1
milliwatt in
600
Q. If
used
with
a
600 O
external load,
the
meter
reading
is
expressed
in dbm
and the
reference Ievel
is
auto-
matically
defined.
II
the instrument
is
used
with
loads
difiering from
600
Q
but substantially less than 10KQ,
cor-
rection Iactors
lor
the voltage reduction
in the
attenuator and
Ior the
db
level
may becalculated.
II
the instrument
is
used
with
high impedance loads, the
relation
between two
signal Ievela
may
be expressed as a number of db difference.
Example:
A device
requi.es
a signal
of
.61
volts
on one input
jack
for
a
c€rtain
output.
It
re-
quires
a
signal
of
.012
volts
on another input
jack
for
the sam€ ouiput_ How many db difference
between the two input
jacks?
.61
volts
is
-
2
db (on
meter)
+0
db
(on
attenuator) = -2
.012
volts
is -6
db (on
meter) -30 db
(on
attenuator) = -36
level difference
is
(-Z)
-
(-36)
=
34 db.
NOTE: Theoretically
the input impedances should be equal in the above
example.
The method
described
is generally more
uselul than calculating the power level at each input (using votiage
and input impedance and using the
formula:
P'
Er
z/Ri
db =
l0
log
-'
=
l0
to9
ia2fR'
Ior
equal impedances
this
reduces to:
lE,\Z
Ei
l0
los ---:-
= 20
los
-i
- (Ezl
-
E2
Although
theoreticallycorrect,
erroneous
impressionmay
be
gained
bynsing
the
above approach:
Changing a 10 KO
grid resistor to
10
megohm decreases the power
level by
a
Iactoi of
100
or
20
db.
Yet the input voltage
is
unchanged.
For further information
see:
Langlord-Smith; Radiotron Designer's
Handbook,
4th Ed.
Ch.19
Hide quick links:
Advertisement
Table of Contents
