N Type vs PL-259

Do you feel perplexed by the hub-bub concerning the difference N Type connectors and the venerable PL-259? What is all the fuss about, anyhow?

What We Know

The problem with the PL-259 is that it does not have a continuous characteristic impedance. It has what has been termed a “surge impedance.”

Wikipedia has a nice brief explanation of this as:

Virtually all of the impedance bump and loss is in the UHF female. A typical SO-239 UHF female, properly hooded, has an impedance bump of about 35 ohms. The length of the bump is typically 12 inch, where the female pin flares to fit over the male pin. This bump can be mitigated by using a honeycomb dielectric in the female pin area. Many VHF/UHF amateur operators use special UHF females that maintain a 50 ohm surge impedance

UHF connector – Wikipedia

Those numbers as reported by Wikipedia should not be taken as Gospel but the underlying qualitative physics are correct. The PL-259 connector center pin has a distance change for about a half-inch which causes an change in impedance. The use of the term “surge impedance” is also probably not the best descriptive term as this implies a dependence on the input signal to temporarily change the impedance.

Let’s Look at Experimental Results

We found a nice article by a blogger who calls himself IZ2UUF.net. In this blog post, he pits the PL-259 against an N-type connector. You can read the entire post if you like, but the significant item of information is the illustrative nature of the “bump” as shown by the figure on the right.

This figure compares a PL-259 (the black “bumpy” curve) with an N-type connector for characteristic impedance (Zo) as a function of frequency. In the figure, you can see that the N-type connector’s Zo remains constant while that of the PL-259 dips noticeably at about 430 MHz. The dip is about 5 Ohms.

What Does This Mean?

It means that the “impedance bump” does not amount to a whole hill of beans affecting overall transmitter station effectiveness. Therefore, it is clearly not worth your while to change out your PL-259 connectors for this reason alone. But if given a choice on what systems to base a new station upon, N-types should be looked upon with favor.