The development and characterisation of an interferometric radio-frequency spectrum analyser based on two surface-acoustic-wave (SAW) Bragg cells illuminated by a semiconductor laser are reported. The local oscillator reference waveform is generated by a repetitive 31 bit pseudorandom noise sequence driven at 250Mbit/s, biphase modulated onto a suitable carrier. Spectrum-analyser measurements demonstrate a channelisation accuracy of 8MHz and a two-signal resolution of approximately 16MHz. For a collimated laser power of 11 mW, a dynamic range of 53 dBhas been achieved for signal pulses with 100 ns duration.