The inherent precision and ambiguity in the measurement of ionospherically reflected echoes by digital ionosondes, which utilize interferometric receiving arrays, depends on the transmitted pulse set pattern, the receiving array configuration, and the data analysis scheme. Building on earlier work carried out for the National Oceanic and Atmospheric Administration HF radar <Grubb, 1979> by Pitteway and Wright <1992>, we use six phase parameters (&PHgr;o, &PHgr;x, &PHgr;y, &PHgr;i, &PHgr;p, and &PHgr;f) to derive echo location, Doppler shift, and wave polarization. We have applied the method of least squares to determine the precision and a ''zero-freedom'' technique to derive the ambiguity associated with each of the phase parameters. Three criteria can be specified which lead to an optimum design of the system parameters: (1) the phase parameters must have aliasing values equal to 2&pgr;; (2) the relative confidence limit factors of the derived phase parameters should be as small as possible; and (3) there must be no aliasing of echo location. By varying the array configuration, frequency pattern, the number of pulses per pulse set, and the number of parallel receivers and receiving dipoles, various designs have been analyzed, and an improved configuration has been obtained. We have shown that various arrangements of the four-pulse, two-receiver configuration can reduce the sum of the relative uncertainties in the phase parameters found for the WERPOL array by up to 33% and improve the ambiguity in each of the derived phase parameters to 2&pgr;.