This read-write UpstrmFreqKhz attribute holds the ComPort's RF transmit frequency; changing it causes the unit to hop to a different receive card, with the ComController validating the change and performing the actual RX-card interface, and the real change applied to the ComPort via a GO_SET message. It's the mechanism used to move an individual STU off a congested or faulty upstream receiver onto a different one without a physical reconfiguration. For example, an engineer rebalancing load after adding a new RX card would write a new stuXmitFrequency to a subset of STUs to shift them onto that card's upstream channel.