Receiver Adjacent Channel Rejection Testing

Test Description

The adjacent channel rejection testing is an extension of the receiver weak signal performance. The test configuration is similar to the previous discussion on BER testing basics in my last post.. This time, we will look at  verifying the sustainability of  receiver performance while an interferer signal is introduced.

Test Setup

The general setup is shown in in the lead in figure. Depending on how the DUT is specified, the receiver should have the ability to reject an adjacent signal of a given strength. We are not looking for the same performance as the DUT’s path-loss with no other interference. In this case it’s usually looking for a acceptable threshold of BER at about +10 to +15  dBm from the previous floor. For instance, you may allow your DUT to insure no BER at -75 dBm  while an adjacent channel is interfering at -60dBm in proximity.

In order to emulate this on the bench you still need to take the the cable and connection losses into consideration. With the AP set for 12 dBm, and the losses to the DUT through the system equal -7.5, to have the DUT experience -75 dBm path loss, the attenuator needs to be set to – 70.5  ( AP Tx – Connection losss -75 dBm). This can be monitored on the power meter in the set up.

Initialization parameters

Set the test channel on for the DUT on the Telemetry AP Unit and adjust the variable attenuator to a transmitted power level of –75dBm @ test channel as read on the power meter.  The external signal generator ( ESG)  transmitted power level will be –60dBm @ adjacent test channel frequency. Set the ESG signal generator to the center frequency of Channel +1 and Channel -1  around the test channel and measure it’s power at the meter. Adjust the power at the ESG to read -60 dBm at the meter.

Test Procedure

The Adjacent Channel Rejection of the DUT shall be tested by means of measuring the BER of the receiving signal sourced from the telemetry’s AP Unit in the presence of an interferingsignal provided by an ESG operating continuously using the same modulation scheme. Check to make sure the BER measured passes under the above mentioned condition.

For each channel tested, set the ESG to +/- 1 channel away, testing twice for each channel.

I hope you found this helpful. Feel free to drop me a comment.