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Model 415Е
3-52.
А system
error
occurs
when
making meas-
urements on lower 415E ranges due tonoise, For con-
venient reference,
a graph
(Figure 3-12)
is shown to
allow correctionto meter reading forany given meas-
urement.
To use this graph, make a signal measure-
ment, then turn RF power
source
off or disconnect
detector from RF source andnoteaverage meter read-
ing due to noise.
Тһе
difference
between these two
reading is used to obtain the proper correction factor
from Figure 3-12.
For example: if the average noise
level is 9.5 db and the measured signal level is 3.5 db
then the difference is 6 db.
Refer to Figure 3-12, 6 db
corresponds
to an
error
of 0.1
db.
This 0.1 db
correction factor is always added to measured signal.
Hence, 3.5 + 0.1 = 3.6 db (corrected meter
reading).
3-53. USE OF CRYSTAL DETECTORS.
3-54.
The input impedance of Model415E must always
be higher
than the output
or source
impedance
of a
02152-1
Section ПІ
Paragraphs 3-52 to 3-56
bolometer or crystal detector connected to the INPUT
connector (see Paragraph 4-21 for discussion). For low
output
impedance
devices,
such
as
100 to 200 ohm
detectors,
use 415E XTAL IMPED/LOW
switch posi-
tion.
For high output impedance
devices,
such as hp
Models 420B, 423B, 424B, or 786D, use 415E XTAL
IMPED/HIGH position. If improper input impedance is
selected, the crystaldetector may depart from square-
law for which
415E is calibrated.
Paragraph
3-55
gives method of checking and calibrating а detector for
square-law response.
3-55. CHECKING
SQUARE-LAW
RESPONSE.
3-56.
Increase the power leveltothe crystal detector
by known
increments
and note
detector
response
on
415E.
Note: a deviation in square-law response may
be due to excessive
RF power to the crystal detector
(see
Operating
literature
for
specified
response
characteristics of crystal detector in use).
3-11/3-12
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