Antenna connectors used in the FPV hobby

In the FPV hobby there are different styles of antenna connectors - let’s take a look at all of them, what their pros and cons are and in which situation you might prefer one over the other.

First let’s take a look at how to quantify an antenna connector - what makes an antenna connector a good antenna connector? The single most important thing with antenna connectors, basically with any connector is, that it has a reliable connection. But how do we define reliable? Reliability depends highly on context.

In regards to antenna connections in FPV we want the following qualities:

Tight fit - The antenna should not unplug too easily. You do not want to have to search for the antenna after every crash.
Lossless - or at least as little loss as possible. Every connection that is introduced into a system brings some kind of loss with it - the signal coming out after the connector is slightly worse than it was before it entered the connector. The material used should be as conductible as possible - gold contacts are optimal. Often times antenna connectors are gold plated to improve their conductivity and keep losses at a minimum.
Easy to swap - we want to be able to easily swap an antenna once it is broken or just to try something different, so the connector should be rated for a decent amount of mating cycles. Generally speaking you want to unplug your antenna connectors as little as possible since even the ones with a higher mating count are still only rated for a couple of hundred times.

SMA/RPSMA

SMA (Sub Minature Type A) and RPSMA (Reverse Polarity Sub Miniature Type A) are very common connector types for video transmitters and receivers. Nearly all of the FPV goggles use this kind of connector and most video transmitters that are used on five inch quadcopters also use this connector. The SMA connector is also a very popular choice on radio transmitters for attaching external antennas.

With SMA connectors the male part of the connector has the threads on the inside and thus the female part is the one with the threads on the outside.

The difference between SMA and RPSMA is the position of the pin - with SMA connectors, the male part of the connector has the pin, with RPSMA the female part of the connector has the pin. When buying antennas - make sure you buy the right one for your system - I highly recommend choosing the same system for transmitter and receiver and then sticking to it in order to avoid confusion.

There is nothing worse than screwing a male RPSMA connector on a female SMA connector - it does fit - but you will not have a proper connection and in the worst case you might burn out your transmitter.

SMA connectors are usually made from brass or stainless steel and are often gold plated.

Pros

rigidity - SMA male and female parts are screwed together and the connection is thus very rigid - you most probably will not simply lose a SMA antenna during a crash.
Relatively high amount of mating cycles - about 500. From this number you can see, that you should better leave your antennas plugged in if at all possible.
Just one type of antenna for transmitter and receiver - as mentioned before, most FPV goggles use this connector, so you can use your antennas on either transmitter or receiver.

Cons

Chunky - you most probably will not use a SMA connector on a whoop style build - they are relatively big and heavy - at least in comparison to the other options.
It is easy to mix up SMA and RPSMA - you always need to double check when ordering, that you get the proper version for your setup.

U.FL

The U.FL connector is known under many different names: I-PEX, IPAX, IPX, MHF and UMMC, but it is all the same connector. This connector was initially designed by Hirose for applications where space is of critical concern, for example the WiFi antenna inside of notebooks. Other companies copied this style of connector under different names but they are all basically compatible with each other.

Those connectors are also made from brass and are gold plated for better conductivity.

The male connector is the one that is mounted to the PCB and has the pin in the center. The female connector is the one on the antenna.

Those connectors are often used for video transmitters on the smaller models.

Pros

Size - this connector is very small and lightweight.

Cons

Very few mating cycles - about 30. This connector was not designed with re-connection in mind. It was rather designed to be used with a pigtail that adapts to something more rigid like a SMA connector.
Little rigidity - the connector is very delicate and can be damaged easily - handle with care when swapping antennas.
They can be easily confused with MHF-n connectors like MHF-2, MHF-3 or MHF-4 which look all very similar but differ in mating height and diameter of the actual connector.

W.FL

This is a smaller version of U.FL. basically the same pros and cons apply as with the U.FL connector. The newer FrSky receivers use this connector.

MMCX

MMCX was designed in the 90ies but is relatively new in the FPV hobby. It is gaining popularity very quickly since it provides a very solid connection with very little weight.

It lies somewhere between SMA and UFL. It is much more rigid than UFL, but since you do not screw the connector on it is not as rigid as SMA, but it is still very safe during crashes. The amount of mating cycles is very comparable to SMA - it is kind of the best of both worlds.

Especially on video transmitters I highly prefer this kind of connector over the U.FL connector.

Pros

Rigid connection - you need to apply some force to connect and disconnect this connector.
Size - quite a bit smaller and lighter than the SMA connector.
Relatively high amount of mating cycles - about 500.

Cons

Not widely spread yet.

Which connector should I use?

I would highly encourage you to go with SMA, simply for the ease of use, interchangeability and availability of different antennas - except if you are going for a small build.

MMCX vs. U.FL

If you are planning a smaller build I recommend to go with an MMCX transmitter, except if it is going to be a very light weight build, then go with the lightest option - a U.FL connector.

Sources:

Chris is a Vienna based software developer. In his spare time he enjoys reviewing tech gear, ripping quads of all sizes and making stuff.

Learn more about Chris, the gear he uses and follow him on social media:

Also check out

Holybro Atlatl VTX

Tinyhawk RTF Review