OPTION 008 RF PROFILES AND COMPLEX SWEEP
Annex-B-15
Suppressing attenuator changes
In addition to being used with RF profiles and RF offsets, sequence sweeps can also be used in
conjunction with Extended Hysteresis. Sweeps generated with the Extended Hysteresis mode
enabled, will use the modified electronic control facility to apply the RF profiles and to vary the
RF output level. Provided the required level does not exceed the Extended Hysteresis electronic
control range the mechanically actuated attenuator will not be operated.
Tutorial example for immunity testing
Example: Immunity testing in a GTEM cell
Problem:
A device is to be tested to check its immunity to electro-magnetic fields using a GTEM cell. The
test requires that the device is tested for field strengths of 10 V/m at frequencies from 1 MHz to
100 MHz and 3 V/m from 100 MHz to 400 MHz. The tests call for checks to be made at 10 kHz
intervals from 1 MHz to 30 MHz, 12.5 kHz from 30 MHz to 100 MHz and 100 kHz intervals from
100 MHz to 400 MHz. The GTEM system requires a nominal signal of -10 dBm to drive an
amplifier that provides a 10 V/m field strength in the cell.
Solution:
The test requires a combination of the sequence sweep, RF offset and RF profile facilities. In this
case the "RF Levels" required at the remote point are field strengths of 10 V/m and 3 V/m. The
RF offset facility can be used to convert a nominal signal of -10 dBm to a displayed 10 V PD by
using an offset of +43 dB (10 V PD is approxi33 dBm).
Use a field probe to check the field strength in the GTEM cell. With the generator set to 10 V PD
use the RF profile facility to obtain a 10 V/m reading on the field probe for frequencies between
1 MHz and 400 MHz. While creating the RF profile remember that the signal generator software
interpolates between profile points so points need to be entered only when the profile slope
changes. Store the RF profile produced and check that the field strength is substantially constant
as the frequency is changed.
Set up a sequence sweep using segments providing the following characteristics:-
START
STOP
STEP SIZE
RF LEVEL STEP TIME
Segment Number 0
1 MHz
30 MHz
10 kHz
10 V PD
100 ms
Segment Number 1
30 MHz
100 MHz
12.5 kHz
10 V PD
100 ms
Segment Number 2
100 MHz
400 MHz
100 kHz
3 V PD
100 ms
Select a sequence sweep using Segment Numbers 0, 1 and 2. With the RF profile and RF offset
enabled and the device under test inserted in the GTEM in place of the field probe a swept test can
now be undertaken.
The test can be repeated at higher or lower field strength by simply redefining the RF level in the
sweep segments.
When the -HYST flag is displayed the RF level of the generator is not as accurate as normal
modes of operation.
In this example it is assumed that the RF amplifier is capable of generating a field of 10 V/m
at all frequencies and that the amplifier is working in the linear region.