Twin Rod Probes

The relationship of the Twin Rod probe to a Coaxial is similar to that of older, twin-lead, antenna lead-in to modern, coaxial cable. 300 ohm twin-lead cable simply does not have the efficiency of 75-ohm coax. The parallel conductor design is less sensitive than the concentric coaxial. This translates to Twin Rod GWR probes measuring dielectrics of only ƒÃr .1.9. The "open" design also allows more accurate measurement where coating/buildup is possible. A film coating has little effect on performance. However, bridging of material between the rods or buildup on the spacers can cause improper measurement and should be avoided. With a twin-rod probe the electromagnetic field develops not only between the rods, it also expands outward making it more sensitive to proximity effects of objects located immediately around it.