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The properties of three terminal positive and negative impedance convertors are defined in terms of the cofactors of the indefinite nodal admittance matrix, the special cases of the ideal transformer, power amplifier, and voltage and current inverting negative impedance convertors being considered in detail. The nodal admittance matrix of a six-node resistive network with two infinite gain amplifiers embedded in it is discussed, and element values are obtained to realize the required analog circuits with a minimum number of components. The analog circuits obtained are simple to set up and are ideal for demonstrating and testing applications of impedance convertors to filter network realizations. Of particular interest is the circuit obtained for the case of a loaded, phase-reversing, positive impedance convertor, which employs only one operational amplifier and four resistors in a bridge circuit, which is thought to be novel, and which can be extended by the introduction of a second amplifier and three resistors to produce a simple realization of a negative impedance invertor (NIV).