Abstract: In a first aspect the present invention provides a method of producing an ultra wide band signal in which (I) a carrier signal is modulated by a spreading waveform which is a periodic deterministic wideband signal and (II) the frequency of the carrier signal is changed by a predetermined amount at predetermined intervals (the reciprocal of this interval being the hopping rate), wherein there is a harmonic relationship between the carrier frequency, the predetermined amount of frequency change, and the period of the spreading waveform. In this way, an ultra wide band signal is created using both direct sequence and frequency hopping techniques and the signal so created may be detected using a coherent detector at a receiver. This provides a wide bandwidth signal, or even an ‘ultra wide bandwidth’ (UWB) signal which mitigates the problems of multi-path signals (through coherent combining across a wide bandwidth) and also interference.