Connector Basics

Contributors:

SFUptownMaker, bitsmashed

SMA Antenna Connectors

Next up is the explanation of the confusing naming conventions for SMA connectors. If you would rather not understand why the convention is the way it is, you can just look at the 4 pictures and move on. Otherwise, have fun with the read!

RF Connector Conventions

SparkFun uses SMA-type connectors on a few boards that need a 50 Ohm impedance connection to an external antenna (GPS, Bluetooth, cellular, Nordic, and XBee). However, some of these boards use different genders and polarities of the SMA connector. Therefore, we need different antennas to match the specific gender or polarity of the RF connections.

There are 4 different types of SMA connectors using a combination of gender, which refers to the center pin and polarity, which refers to…..uh, this is where it gets confusing. Wikipedia tries to explain it. But from what I have found there was an original “old” design for SMA connectors.

SMA Connectors

The original SMA design called for two compliant connectors:


SMA Male Center Pin, Inner Threads	SMA Female Center Hole, Outer Threads

The above two connectors were designed to be used together, but there was a problem with this configuration and the FCC started moving towards Part 15 compliance. All this means is that all the SMA RF connectors are changing gender (center pin). Really annoying for those of us who need to mate an antenna to an RF device. The FCC gender change was instituted to prevent home users from damaging RF equipment (think home WiFi) when screwing on an antenna. If all antennas are female, there is no way to damage the center connector.

There is one consistency however; all antennas, cables or anything was being attached to a potential stationary object used an outer nut or inner thread design and all stationary devices used the outer thread design. This applies for all SparkFun products. All of our antennas are either SMA male or RP-SMA female. All of our boards are either SMA female or RP-SMA male.

RP-SMA Connectors

The only thing that changed with the Part 15 compliance was the center pin, thus reversing the polarity of the connection and forming a “new” standard; the reversed polarized SMA (RP-SMA). The RP (reverse polarity) is named after its “thread gender” and has an opposite-gender pin.

The next two photos are considered reversed polarized (RP-SMA).


RP-SMA Male Center Hole, “Male” Inner Threads	RP-SMA Female Center Pin, “Female” Outer Threads

If the board does not have a u.FL connector to attach an external antenna, SparkFun RF boards and antennas will use a combination of the old (SMA) and new (RP-SMA):

Cellular and GPS (900/1700/1800MHz and 1.57542GHz respectively) generally use the old convention: SMA male for the antennas and SMA female for the modules.
Anything 2.4GHz (Bluetooth, ZigBee, WiFi, and Nordic) generally use the new convention: RP-SMA male on the antennas and RP-SMA female on the modules.

Really, you can ignore the gender descriptor. If you have a RP-SMA board or module, you need a RP-SMA antenna and so forth for SMA. Pretty simple, right?! Just make sure to match the antenna frequency with the your board.

And just in case if you happen to find the old and new mixing, we sell a SMA male to RP-SMA male and a RP-SMA female to RP-SMA male connector that will most combinations of antenna and connector to be mated.