FAQs from Rohde & Schwarz

AC CPL displayed on EMI Receiver.


I have a AC CPL issue displayed on the Receiver.

Why does this message appear and what is the lower frequency limit of the device for AC coupling?


This is no device issue. This is a normal behavior of your Receiver. The message does show you, that the AC-Coupling for RF input was selected.

You can change this setting in the Input/Output menu. If it will be set to DC-Coupling, there will be no information in your display.

Please refer to the Specification of your EMI Receiver. For e.g. ESR, ESRP and ESW with AC coupling activated, instrument is specified from 10 MHz. Please download instrument specifications from instrument website for details.With DC Coupling no DC voltage is allowed on RF input, otherwise instrument may become defective. You can understand AC coupling as some kind of capacitor at RF input .It acts as a DC block with high-pass characteristic. It takes more into effect, as lower the frequency is. Therefore you can only have correct level readings from this higher, specified start frequency. In other words: If you need correct level readings for frequencies below, you have to select the DC coupling, but make sure that you do not have any DC on RF input.