Equipment and materials

The 2120 frequency analyser is a constant percentage bandwith analyser for use in the frequency range 2Hz to 20kHz with provision for the connection of external filters extending the range to 180kHz. It consists of a measuring amplifier combined with a built‐in active RC filter complex which is continuously variable and can be switched into four basic modes. It can be used as a constant relative band‐width filter having four selectable bandwidths of 1 per cent, 3 per cent, 10 per cent and 1/3 Octave; as a tunable bandstop filter which will suppress any chosen frequency more than 60dB, suppression at 0·5fo and 2fo being less than 1dB; as a tunable high pass filter, or as a tunable low pass filter.