AWT PIM-P, Руководство пользователя, Страница: 87 / 110

10-3
PIM-P Analyzer User’s Manual
Copyright AWT-Global, LLC. All rights reserved.
10.2
How to test PIM
PIM testing for field applications requires the injection of two CW signals (f1 and f2)
into a system under test. Intermodulation products (IM) of the 3rd, 5th, 7th… order, caused
by faulty components, appear immediately. The strongest intermodulation product is
usually that of the 3rd order (IM3). Frequencies of these intermodulation products can be
calculated as follows:
f
IM3L
= (2 x f
1
) – f
2
f
IM3H
= (2 x f
2
) – f
1
The picture below shows an example of passive intermodulation. Frequencies f1 (869
MHz) and f2 (894 MHz) are located in the Tx range, causing intermodulation f
IM3L
(844
MHz) and f
IM3H
(919 MHz). Both IM products can cause serious interference.
A visual example of intermodulation is caused by two CW signals. Ideally, test
frequencies f1 and f2 should be at the edge of the transmit guard bands, so that the IM3
products f
IM3L
and f
IM3H
fall at the edge of the receive band(s), usually utilized as guard
bands. This minimizes interference within the system under test and also eliminates
potential interference in other wireless bands
IM3 serves as an example. With IM3 as a result of PIM, other IM products (IM5, IM7,
IM9, IM11, …) will be present as well, and can impact base station performance
significantly.