I inadvertently ordered the wrong pigtail for my setup. So, a few notes for future reference…
A WRT54GL router uses RP-TNC connectors. The TNC (threaded Neill-Concelman) connector is a threaded version of the BNC connector. The connector has a 50 ? impedance and operates best in the 0–11 GHz frequency spectrum. It has better performance than the BNC connector at microwave frequencies. Invented in the late 1950s and named after Paul Neill of Bell Labs and Carl Concelman of Amphenol, the TNC connector has been employed in a wide range of radio and wired applications.
Reverse-polarity TNC (RP-TNC) is a variation of the TNC specification which reverses the polarity of the interface. This is usually achieved by incorporating the female contacts normally found in jacks into the plug, and the male contacts normally found in plugs into the jack. RP-TNC connectors are widely used by Wi-Fi equipment manufacturers to comply with specific local regulations, i.e. those from the FCC, which are designed to prevent consumers from connecting antennas which exhibit gain and therefore breach compliance. This is the case for the popular Cisco line of Wi-Fi products. RP-TNC can also be abbreviated as RTNC.
The N connector (in full, Type N connector) is a threaded RF connector used to join coaxial cables. It was one of the first connectors capable of carrying microwave-frequency signals, and was invented in the 1940s by Paul Neill of Bell Labs, after whom the connector is named. The N connector follows the MIL-C-39012 standard, defined by the US military, and comes in 50 and 75 ohm versions. The 50 ohm version is widely used in the infrastructure of land mobile, wireless data, paging and cellular systems. The 75 ohm version is primarily used in the infrastructure of cable television systems. Connecting these two different types of connectors to each other can lead to damage due to the difference in diameter of the center pin. Unfortunately, many type N connectors are not labeled, and it can be difficult to prevent this situation in a mixed impedance environment. The 50 ohm type N connector is favored by enthusiasts who create their own Wireless LAN antenna systems, which run at 2.4 GHz or 5 GHz. The Cantenna is one such design. The enthusiasts have settled on using the N connector as a standard connection for homebrew antennas. By using a cable with an N connector one can easily interchange homebrew antennas. 50? N connectors are also commonly used on amateur radio devices (e.g., transceivers) operating in UHF bands.
Pictures and descriptions can be found at: http://wireless.gumph.org/content/3/7/011-cable-connectors.html