This read-only UpstrmFreqKhz object reports whichever frequency -- primary, alternate A, or alternate B -- the RX port is presently using, and the description notes it always matches the primary on initial deployment and returns to this active value after a reboot. An admin reads it to find out in real time whether the port has hopped away from its primary frequency. For example, seeing hcxUpstrmActiveFreq differ from the configured primary frequency tells the admin a hop event occurred and prompts them to check the RF analysis counters for the cause.