Interferometer Baseline

Most interferometers for radio astronomy are built on an east-west baseline and although this is not strictly necessary the operation of an east-west interferometer is the easiest to visualise. Also it is the easiest to interpret as the fringes recur more rapidly than those of any other baseline.

So how long should the baseline be?
In the vicinity of the meridian a baseline n wavelengths long would produce n/4 fringes per hour when a source on the celestial equator is observed. For example if the wavelength was 4 Meters (e.g. 74Mhz) then a baseline of 80 metres or 20 wavelengths would have a fringe rate approximately 5 fringes per hour or a fringe every 12 minutes.