An apparatus comprises a sampling circuit configured to sample transmit and receive signals of a first radio node to be transmitted to or received from a second radio node. Transmit-side and receive-side envelope detectors are configured to produce transmit-side and receive-side envelope signals based on sampled transmit and receive signals. A transmit-side time measurement unit is configured to generate, based on the transmit-side envelope signal, a transmit-side marker signal based on a pre-defined transmit-side threshold, measure at least one first time delay between at least one time start pulse and at least one marker of the transmit-side marker signal and store to a memory and/or output said at least one first time delay. A receive-side time measurement unit is configured to implement the corresponding functionalities as described for the transmit-side time measurement unit in the receive-side.