Abstract: Disclosed are digital data receivers, methods and circuitry for differentiating between signals and data packets of varying physical layer protocols and frequencies transferred over a digital burst mode communications system, such as a packet-based LAN. Transitions in a received input signal to a squelch circuit start a counter which asserts one or more signals at various predetermined times from the transition. The absence or presence of the signal when the next transition in the input signal occurs indicates whether the input signal is less than or greater than a frequency associated with a particular predetermined time interval. When a predetermined number of transitions meeting a particular frequency requirement are received, the input signal is determined to be received at a particular frequency.