2.11 Measuring Radio
Frequency Power
Variable
transformer
0
Electronic Wattmeter
Chapter 2
Power at frequencies outside the range of the
EW604 can
be
measured using a photometer
as
in
fig
2.1
0.
To measure the power output of a radio frequency circuit, the
switch is set to position
1 and the location of the grease spot
photometer adjusted
so
that the illumination of lamp L
1
(radio
frequency
load) equals L
2
. When this occurs the grease spot
disappears.
The switch is then set to position 2 and the autotransformer
adjusted
till the grease spot again disappears. When this occurs
the
EW604 gives the same indication
as
the power output from
the radio frequency source.
Amps
•
Voltse
00
::():: u
supply
Reference
lamp
EW604
~
Radio frequency
circUit
Fig
2.
10
Measuring radio frequency power
20
l2
Grease
spot
photometer
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