The invention encompasses a digital radio transmitter (2), a digital radio receiver (2) and a method of randomising data for digital radio transmission. A first digital signal (S1) contains voice and/or data. A second digital signal (S2) comprises different short pseudo-random data sequences, the second digital signal (S2) changing between different short pseudo-random data sequences at pre-defined time points. Both the order of the short pseudo-random data sequences and the timing of the pre-defined time points may vary in a pseudo-random manner. The first (S1) and second (S2) digital signals are combined to produce a third digital signal (S3) for transmission. A digital radio receiver (2) is adapted to generate the second digital signal (S2), and to use this extract the first digital signal (S1) from the received radio signal.
