A system and method for protecting a cable modem's receiver from transmitter overload when using a splitter/combiner device in place of a conventional (diplex) filter. Instead of a diplex filter to separate transmit and receive bands, a terminal device can use an isolation device, such as the splitter/combiner, or a circulator. This provides an ability to use a frequency band for either upstream transmissions or downstream reception, but creates a problem of receiver overload when the isolation device has insufficient isolation or a back-reflection occurs. Use of agile local oscillators allows the direction of the signal in the band to change very rapidly. Likewise a receive frequency can by dynamically reassigned by retuning a LO, which may employ direct digital synthesis.