Identifying hopping radio transmissions - testing on basis of previously used frequencies in search receiver by time filter function for coincidence

摘要

Radio transmissions with certain transmit frequencies only used for a short time period are identified using a search receiver, scanning a larger frequency range in steps. It recognises used frequencies by a level threshold, or measuring the signal to noise ratio. In the search receiver, the frequencies recognised as used are tested by a time filter function for coincidence with criteria of a short time transmission, i.e. the max. period of a frequency use, min. interval of renewed frequency use, max. interval up to renewed frequency use, and fine measuring of the use duration period. USE/ADVANTAGE - Descrambling or decoding secret messages, using low-cost process.