B.2 Measurement set ups for TX intermodulation

3GPP51.021Base Station System (BSS) equipment specificationRadio aspectsRelease 17TS

The following test set‑ups are examples for possible solutions for the measurements according to subclauses 6.7 and 6.8. These measurements are very difficult to perform due to the extreme requirements of the dynamic range. To get reproducible measurements precautions should be taken, so that non‑linearity’s in the test set‑up do not influence the measurement results.

NOTE 1: Care should be exercised in creating the test set‑up and good quality cables and connectors should be used. Cables should be physically secured and not disturbed unless necessary.

NOTE 2: Connectors should be free of ferro‑magnetic substances. Different surface materials on both connectors as well as the applied torque of the connection have an influence on the intermod‑performance.

NOTE 3: Power attenuators normally have an insufficient intermod‑performance at high power in­put levels. Therefore it is recommended to use long cables for attenuation where high power is applied.

B.2.1 Test set‑up for Intermodulation Attenuation (6.7.)

It is necessary to use different set‑ups for the measurement of IM‑products in the RX band and outside the RX band.

B.2.1.1 RX‑Band

A recommended test set‑up for the intermodulation attenuation in the receive band is illustrated in figure B.2-1. A directional coupler is used with the measurement performed on the primary line connector. Sufficient filtering is provided by the duplexer so that the spectrum analyser operates in its linear range. The injected signal is amplified and filtered to provide sufficient isolation to inhibit self generated intermodulation products in the test set‑up.

Figure B.2-1: Test set‑up for Intermodulation Attenuation (6.7.) RX‑Band

B.2.1.2 Outside RX Band

A recommended test set‑up for the intermodulation attenuation outside the receive band is illustrated in figure B.2-2. The coupling device shall be specified to operate over sufficient bandwidth to comply with the measurement requirements.

Figure B.2-2: Test set‑up for Intermodulation Attenuation (6.7.) outside RX‑Band

B.2.2 Test set‑up for Intra BSS Intermodulation Attenuation (6.8.)

It is necessary to use different set‑ups for the measurement of IM‑products in the RX band and in the TX band.

B.2.2.1 RX‑Band

A recommended test set‑up for the intra base station intermodulation attenuation in the receive band is illustrated in figure B..2-3.

The stop band attenuation of the duplex filter has to be high enough to guarantee that the spectrum analyser is working in its linear range.

Figure B.2-3: Test set‑up for Intra Base station Intermodulation Attenuation (6.8.) RX‑Band

B.2.2.2 TX‑Band

A recommended test set‑up for the intra base station intermodulation attenuation inside the transmit band is illustrated in figure B..2-4. To decrease the dynamic range requirement of the spectrum analyser external filters should be used.

Figure B.2-4: Test set‑up for Intra Base station Intermodulation Attenuation (6.8.) TX‑Band

Annex C (informative):
Number of samples needed for statistical testing