An apparatus includes a transceiver configured to generate a signal and receive a plurality of reflected signals for measurement of a level of a process fluid in a tank. The apparatus also includes a waveguide comprising a probe and a buoyant part. The probe is configured to guide the signal from the transceiver and the plurality of reflected signals to the transceiver. The buoyant part is configured to move with the level of the process fluid at an end of the probe and produce a secondary signal representing the level of the process fluid when a level signal of the process fluid is within an end signal representing the end of the probe.