Fluke 9640A Series, Instruction Manual

Page: 225 / 324

Calibration
Performance Test
5
5-35
Level Accuracy – 75
Ω
Equipment required for this test:
•
AC Measurement Standard
•
Precision 75
Ω
feedthrough termination
•
75
Ω
Type-N female-to-BNC male adapter
•
Power Meter
•
Power Sensor, 75
Ω
•
Precision Adapter, Type-N female-to-female, 75
Ω
•
75
Ω
to 50
Ω
impedance-matching pad
•
Spectrum Analyzer
•
75
Ω
Leveling Head (supplied with UUT)
Use the following procedure to verify the absolute level accuracy of the UUT 75 Ω
output. The procedure makes use of an AC Measurement Standard, followed by a power
meter and sensors, and finally, a spectrum analyzer/measuring receiver. At various points
within the process values previously measured using one reference device are required
for subsequent use with another device. It is recommended that the users familiarize
themselves with the entire absolute level accuracy verification procedure before
commencing.
Note
Unwanted interference from signals at 10 MHz due to the frequency
reference outputs of equipment operating in the vicinity of the test setup or
the equipment used during the tests can cause erroneous results. In order to
avoid such problems, it is recommended that for test frequencies from 10
MHz to 300 MHz a small offset (50 kHz) is added to the listed nominal
frequency if the test frequency is a multiple of 10 MHz.
1. Connect the 75
Ω
Leveling Head to the INPUT 1 connector on the AC Measurement
Standard using a precision 75
Ω
feedthrough termination. (If a Type-N feedthrough
termination is not available, use a BNC 75
Ω
feedthrough termination and
appropriate adapters. Ensure that BNC connector contact resistance and repeatability
does not significantly degrade measurement uncertainty) Select INPUT 1. See Figure
5-9 for equipment connections.
Note
It is recommended that a common mode choke is used to obtain satisfactory
noise performance and accurate readings. Insert the common mode choke
in series between the feedthrough termination and the AC Measurement
Standard input, with the ground applied at the choke input. Keep the
ground connection as short as possible and set the AC Measurement
Standard to Internal Guard. A common mode choke of 250 µH is usually
effective. A suitable choke is 6 turns of small-diameter coaxial cable
through a TDK toroid, manufacturer’s part no. H5C2-T28-13-16 (available
as Fluke part no. 474908) Refer to section 4-12 of the 5970A Operator
Manual for additional explanation.
Note
Measurements made on the 5790A 2.2 mV range (at levels below -42 dBm)
require correction for the 2.2 mV range linearity error.