FAQ on antenna connectors and connectors for beginners

FPV hobby cannot be imagined without the use of signal transmitting antennas. Over time, many different types of antennas have been connected to electronic components. Let's analyze the types of connectors and discuss the difference between them.

SMA - RP-SMA connectors

The most popular connectors used in many types of model building. They are metal connectors with internal or external threads. Secure nut connection eliminates accidental disconnection of the antenna in flight. The contact is a copper core in the center of the connector, can be differentiated as a pin or hole. The resistance of the connector is 50Ω. Connector width is 8 mm. The connectors differ in the type of screw connection and the type of connection of the contact core.

The standard SMA connector type is categorized into two types, SMA Plug and SMA Jack.

• Plug refers to the type of threaded connection in the form of a nut with threads inside. In the SMA Plug connector, the contact core is always in the form of a pin.
• Jack, on the other hand, is a connector with a thread on the outside for screwing on the Plug connector. With an SMA Jack connector, the contact core is always in the form of a hole.

Some manufacturers identify them as SMA Male and SMA Female, according to the type of contact core design.

However, connectors labeled RP-SMA have the reverse type of contact core design. RP stands for reverse-polarity, but this refers only to the appearance of the connector's contact core, not the physical properties of the signal. Thus, the connectors change the type of contact core design, but the name remains the same, but with the prefix RP. The SMA Plug(Male) connector has a hole instead of a core pin, the nut and thread type remains the same, and it is called RP-SMA Plug(Male). In the RP-SMA Jack connector, on the contrary, the core pin appears, i.e. it becomes "Daddy", but with the same male thread as shown in the picture:

There is no compatibility between SMA and RP-SMA, you must choose connectors with the same labeling.

The following table shows the ratio of connector name to connector type:

IPEX Connectors

Connectors of this type are used to connect antennas and video transmitters, radio receivers. They are characterized by a quick and easy way of connection, which is done by snapping the connector. They are designed for a small number of connection cycles (about 30), after which it is desirable to replace the connector with a new one. Connector resistance is 50Ω, bandwidth up to 6GHz, connector dimensions on the board are about 4 x 4 mm and 3 mm high, depending on the model the dimensions vary slightly.

In the FPV hobby, U.FL and MHF series connectors are mainly used. They are also categorized into different models that have different dimensional characteristics.

• U.FL connectors are mostly used to connect antennas to video transmitters. They have a Male version, which is mounted on the board, and a Female version, which is crimped directly to the antenna or cable.
  
• To connect the antenna to the signal receiver from radio equipment such as Frsky R-XSR or use MHF4 connectors. They have a smaller size and a different type of design, also divided into Male and Female. Connector height is 1.2mm, compatible cable sizes for Female connector are 33AWG and 36AWG.
  
  
  

The pictures show the visual difference of the connectors and their sizes (clickable):

MMCX connectors

Manufacturers of electronic components listened to the advice of FPV community and started to use MMCX connector for video transmitter antennas. It is a snap-in connector with stronger contacts than IPEX and with the ability to rotate the contact in the connector 360 degrees. The connector is available in straight and 90 degree angled versions for easy connection to different video transmitters. Connector resistance is 50Ω, bandwidth up to 6GHz, the declared number of open-circuits more than 500. Compact and easy to use connector is becoming popular in FPV components. It is divided into Male (Plug) and Female (Jack) connector. Female connector is soldered to the electronics board in most cases, Male connector is crimped to the antenna wire.

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