# ROVL Channels Mk II Autosync units with receiver software after August 9, 2021, can be set to receive on either or both ROVL channels simultaneously, allowing you to track up to two transmitters simultaneously. When in this mode a $USRTH message is sent for each channel once per second. CeruleanTracker provides an option to select which channel is to be the “active” channel. The active channel is used for the combined ROVL/DVL ROV position solution and/or the unfiltered ROVL position. $USRTH messages received from the channel that is NOT active are ignored, except they are sent to the Cerulean Map application to be displayed as a secondary item. ![The active ROVL channel is selected using the radio buttons on the ROVL Command Window.](/files/95kdqRBehPaiRFlC5A2l) {% hint style="info" %} Note: if you are using a Mk I unit or a Mk II unit without autosync, selecting channel B as the active channel will make your ROV effectively invisible. {% endhint %} ### DVL Command Window --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.ceruleansonar.com/c/ceruleantracker/overview/operating-ceruleantracker/input-device-configuration-panels/rovl-channels.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.