Linear Dummy Loads

The need for linear dummy loads is established. It is indicated that nonlinear dummy loads generate predominantly oddorder harmnonics. A theoretical analysis is presented which demonstrates that an ¿infinite¿ coaxial cable with an infinite load (open circuit)at the output has an input impedance equivalent to the cable´s characteristic impedance Z0. An equation is derived relating the voltage standing-wave ratio S, cable length h, and the cable attenuation constant ¿. The linearity of a cable load is compared with the linearity of ¿typical¿ commercially available loads and the commercial loads tested are found to generate 20 to 80 dB more third harmonic. Cable selection guidelines for a linear coaxial cable load are presented.