The radio connection for the FPV image between quad and goggles requires analog antenna connectors. There are four different connectors for the screw connections: SMA, RP-SMA, and IPEX. I would like to describe here briefly how I can keep them apart.
SMA vs. RP-SMA antenna connectors
The first thing is to figure out which of the two systems you are using in the first place. To do this, I always look at the male connector. You can recognize it by the internal thread, i.e., it is “screwed” onto the other one:
If I am clear that I have the male connector, then I look inside. If there is a plug, I am with SMA if there is a hole with RP-SMA.
Male vs. Female antenna connectors
As mentioned above, you can’t tell from the inside of the plug (the pin) whether it’s the male or female plug. I found this a bit confusing at first. Only the thread is responsible for this distinction.
If the antenna connectors are screwed on, i.e., it has an internal thread, it is the male connector. On the FPV goggles, it is usually what comes out of the receiver module.
As a mnemonic: SMA is the “right” system because there the male connector also has a pin inside.
Other antenna connectors for VTX
There are other plug-in connections for video transmission. These are mostly used on smaller 20x20mm boards.
IPE-X are another coax antenna connectors. It is often a bit fiddly to the plugin: The plug has to be really flat parallel when connecting — small wrong angles will hardly be forgiven. But afterward, you have a quite flexible connection because it can be rotated.