In radio navigation systems located in areas that are rich with interrogation reflections a variable dead time provides smearing of replies during the interrogation time window generated by the interrogation reflections. A radio navigation system of the type described receives a pair of interrogation pulses which are decoded into a single pulse for operation of a reply transmitter. The interrogation pulse receiver decodes the interrogation pulses only during the active time span thereof and when received interrogation pulses are spaced over the required time span. The transmitter generates position determining signals in response to the decoded interrogation pulses. To block-out or smear the position determining signals emitting from the transmitter generated by interrogation pulse reflections, a variable width blanking pulse is generated for deactivating the interrogation pulse receiver. This variable width blanking pulse is generated in an anti-synchronous circuit responsive to the decoded interrogation pulses and timed clock pulses.
ANTI-SYNCHRONOUS REPLY CIRCUIT