noted above the prior art receive aperture control system has a significant drawback in that it requires three separate firings of the elements of row 14a in order to accumulate the necessary elevational information referring now to fig4 a receive aperture control system of this invention is illustrated that overcomes this inadequacy of the prior art as with the prior art receive aperture control system of fig3 the control system of the invention may be disposed within the transducer 12 or the receiver 22 or may be distributed between these two structural elements particularly the receive aperture control system comprises a single high voltage multiplexer 46 coupled in series with a pair or multiplicity of parallel connected low voltage multiplexers 42 44 the low voltage multiplexers 42 44 are coupled to the elements of rows 14b 14c respectively the low voltage multiplexers are capable of switching at a much faster rate than the high voltage multiplexers of the prior art with much less of a switching glitch notwithstanding this benefit the low voltage multiplexers are far less robust than the high voltage multiplexers and are not capable of withstanding the high voltage differential produced by firing of the active row elements 14a accordingly the high voltage multiplexer 46 is used to protect the low voltage multiplexers.