SMA Adapters: determining correct gender
Channel: Mountain Parameters
Date: 2020-09-25

The design of SMA terminals often leads to confusion with respect to determining the correct gender. For example we often get an order for an SMA-M antenna to fit a BaoFeng radio, which is incorrect because typically, Chinese budget radios are found with an SMA 'reverse polarity' connection on them. (Because our SMA-M antenna base also has a pin in it, we are looking at a pin on each side of the connection.) At the present time, the BaoFeng's and many budget recreational radios use an antenna that has an RP-SMA-F connection on it. It does not help matters that you never seem to see a seller's listing on Amazon or Ali for a BaoFeng radio that makes it clear that it uses a 'reverse polarity' connection. A common perception is that because the neck of the connection fits into a recess on the opposite side, it is male, and this is strictly correct because gender is based on the threads. To simplify when ordering antennas, the gender we consider when ordering antennas is based on the pin that resides in the neck of the connector. This then means that when ordering an antenna to fit a BaoFeng or other radio with similar 'reverse polarity' mount on it, you will order an antenna with SMA-F base. This video illustrates this concept to make it clear, and may help you to avoid ordering an antenna with the wrong base connector on it. (*Do not apply the gender descriptions in this video for radio base connections to SMA networking connections for cables.)

*Reverse Polarity: For cabling, you will also see a similar SMA-F type of connection shown here with threads on the outside referred to as a 'reverse polarity' connector. But notice it has a pin in the middle, and not a hole. Reverse polarity is also found on a variety of other connectors such as "N' type, BNC, and TNC, and the pin does not define their gender. To figure out if you have a reverse polarity connector, use this rule of thumb: if the threads are on the outside it is female, threads on the inside are male. If the threads are on the outside, and there is a hole in the middle, it is a standard female connector, if the threads are on the outside and there is a pin in the middle, it is an RP-SMA-F. (If the threads are on the outside and it has a pin in the middle, it is 'reverse polarity'.) Many specialists do not favour the use of this term because in fact the polarity of your network is not actually reversed when you use one or the other, but if you are ordering a piece of equipment that says it has a 'reverse polarity connector' on it, then your cable will have to have the threads that correspond. So the bottom line is, if you see the term 'reverse polarity' mentioned when you are buying something, make sure that whatever you are attaching to it has the correct mating form factor because the pin is what defines the 'polarity'. You'll often notice a rant in forums that throws shade on a radio manufacturer for using a connector that requires the use of an SMA-M antenna or cable. The reason the SMA-F adapter has started to take dominance over use of RP-SMA-F on radios is because it has advantages that improves durability and performance, and we discuss this elsewhere.

Note: not all SMA are created equal. For example the pin mating aspect geometry on the Motorola SMA core is different, so when ordering an antenna for a Motorola model that has an SMA antenna base on it, the buyer needs to specify 'Motorola SMA'.

There is a fair bit of confusion when it comes to ordering an antenna base for Icom and selected Motorola radios because some (such as the Icom F1000 for example), use what is called a "J" thread. This is due to the fact that we offer an MX thread, and not a 'J' thread.

Our antennas are made in the United States. UNC (Unified National Coarse) and UNF (Unified National Fine) threads are both types of unified standard threads that are used in the United States. These threads are designated as such because they are standardized by the American National Standards Institute (ANSI).
Our base with MX threads commonly works on the Icom and Motorola radios. MX, also known as Multiplex threads, are a type of unified standard thread that is similar to UNC and UNF threads, but they have a slightly different profile. 

J-threads, on the other hand, are a type of unified standard thread that is used in Japan. These threads are designated as such because they are standardized by the Japanese Industrial Standard (JIS).

Overall, the main difference between UNC/UNF/MX threads and J-threads is the country of origin and the standardization body that defines them. The difference between unified standard UNC/UNF/Metric threads such as the MX and unified standard J-threads is that the minor diameter of J-threads is curved not squared. Until now, we have been finding that the MX base that Smiley is using, has been working for our clients that fit them to their Icom and Motorola radios that commonly specify a 'J' type antenna thread.