# What are the differences between the electrical length, the physical length, and the insertion length of an adapter?

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What are the differences between the electrical length, the physical length, and the insertion length of an adapter?

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Generally, the overall length of an adapter is considered to be its physical length from connector end to connector end. The insertion length is the length an adapter will add when inserted between two connectors. The electrical length depends on the size and type of dielectric material used in an adapter. It is measured at the mating plane of the outer conductor and is the length of the adapter as it appears to the signal traveling through it. In many instances, the electrical length, the insertion length, and the physical length are very close to each other. In an adapter that has no dielectric, the length of the adapter (measured at the mating plane of the outer conductor) is its electrical length. (The dielectric of air is close enough to “1” that its effects can usually be ignored.) This is not the case with most adapters which contain some dielectric material. The electrical length of the adapter needs to be calculated for that portion of the adapter that contains the dielectric.