FPV Connectors: SMA, RP-SMA, MMCX, U.FL

SMA (RP-SMA), MMCX and U.FL are the three main types of connectors used in FPV transmitters, receivers and antennas. This guide explains the differences to help you avoid getting incompatible equipment. The gender of SMA and RP-SMA connectors are just as confusing.

Some people find it difficult to get their heads around the different types. Even manufacturers could sometimes get it wrong. When buying FPV equipment with a SMA connector, we urge you to double check if the product description matches product image. If not, confirm with the seller to avoid surprises.

Table of Content

Differences of RP-SMA and SMA Antenna Connectors

SMA and RP-SMA connectors are the original connectors used in FPV equipment. They are still very common thanks to their robustness and versatility. However they are also fairly bulky and heavy.

Another advantage of SMA is the 500+ mating cycles, which a lot more than MMCX and U.FL. All the receivers I’ve come across use SMA or RP-SMA and rarely use other connectors, because weight and space is not really an issue on the receiving side.

SMA stands for Sub-Miniature Version A. These are coaxial RF connectors developed in the 1960s.

RP-SMA stands for Reverse Polarity SMA). It is a variation of the SMA connector which reverses the gender of the interface.

There is no difference with video/signal quality between these connectors, but you’ll read further down why we even have these 2 different types. Generally speaking, SMA appears to be more popular choice of connector especially in the mini quad (racing drone) industry.

Here is a comparison table of the SMA antenna and RP-SMA antenna connectors.

SMA Female

SMA Male

sma-jack sma-plug

Female SMA connectors have a female contact body (ground) and a female inner hole sleeve contact (signal).

Male SMA is opposite to the Femaile SMA.

RP-SMA Female


rp-sma-jack rp-sma-plug

Female RP-SMA connectors have a female contact body (ground) and a male inner pin contact (signal).

A male RP-SMA connector is the opposite in both respects — male body (inside threads) with a female inner sleeve contact.

For most of us, it would take some time to get to know which was which off the top of our heads. For those who are still getting used to remembering them, an SMA antenna basically has the pin in the middle while the RP-SMA antenna is the exact opposite with a small hole in the centre. It’s not that hard so I’m not coming up with a nursery rhyme to remember it like some others do. :-)

SMA to RP-SMA Adapter – Angle Connector

If you happened to have antennas of the wrong connector, you can get an adapter for it. Some even come with angle to make antenna mounting more flexible.

However note that there is some performance loss to every adapter you use. So avoid it whenever possible.

Removing/Changing SMA Connectors

Many will often replace the connector with the ones they prefer or may choose to add a “pigtail”extension” on the video transmitter to save the components from breaking off.

Whether you are just adding a pigtail or directly soldering the antenna to the VTX, the same steps apply to both. This is a very useful trick and quite easy to do with a bit of soldering skill.

For replacing RP-SMA to SMA or vice versa (on video transmitter), simply cut off the bulk of the connector with some wire cutters or dremel cutting wheel, and use your iron to remove the remaining little legs off the VTX surface. If you’re really handy with an iron or have a heat gun, you can remove it without needing to cut anything off.

The signal line runs inside along the middle separated from the ground shielding by a silicone or plastic layer. Do not accidentally short signal and ground when soldering.

When doing the pigtail mod

  • Cut off the end you don’t need and strip back approximately 3-5mm of the outer coating exposing the first ground shield layer
  • Pull the few mm of ground wires back to expose the middle section of the cable
  • Strip just the tip of the signal coating about 1mm to expose just the tip of the signal wire
  • Tin both the ground and signal separately, you can split the ground into 2/3/4 separate strands depending on how many ground pads there are to solder to.
  • Be sure there is enough length so the grounds won’t touch the signal wire; Be sure to note which pins/pads are the grounds and the signal
  • Solder the signal first to the corresponding pad (usually the centre pad) and then start soldering on the surrounding grounds.
  • Last step is to find a suitable place for the connector, most usually mount it to the frame away from the receiver antenna on the quad. Voila, a crash proof VTX connector!

VTX’s that come with pigtail

If you’re not so handy with the soldering iron or don’t even want to consider such a task, there are many vendors out there now that sell VTX’s with pigtails already installed or have a variety of mounting and connector options to suit your builds.

U.FL Connectors

As known as IPEX connectors sometimes, U.FL has been a popular connector choice in many small size video transmitters and antennas. They are also very popular in radio receivers due to their compact sizes.

The connector has no thread, it’s attached by popping them together. They are a lot more fragile than standard SMA/RPSMA connectors and they have a very limited mating cycle, only about 30+, according the datasheet.

But in the never-ending search for shaving weight, this can be a great choice. Current options with this type of connector including the TBS Unify Pro HV and the Immersion Tramp HV.

UFL to SMA Adapter

MMCX Connectors

SMA is too big and heavy, U.FL is too fragile, and the MMCX is the great balance of the two!

MMCX connectors are slightly smaller and lighter than SMA connectors, but much tougher than U.FL. Rated for 100+ mating cycles, more and more VTX and antennas are picking up this connector and we can only expect it to play a bigger role in FPV.

MMCX to SMA Adapter

Some Interesting History about the RP-SMA Connectors

The intent behind creating RP-SMA was to comply with specific local regulations. The manufacturers had to make a new non-standard antenna connector for their WiFi devices that was hard to find replacements for (as they were all regular SMA before that), to prevent consumers from connecting antennas with gain and therefore breach compliance (from Wikipedia). So they just simply swapped the locations of the centre pin and hole between the male and female connectors.

The term “reverse polarity” here basically means the change of gender. It might confuse those who are not WiFi engineers, as polarity elsewhere in radio frequency literature can refer to the electromagnetic polarity, not to a change of gender.

Hopefully this helps clear up the differences and provides some useful tips. If you have any suggestions or comments please leave them below. Thanks for reading and happy flying!

Edit History

  • Jan 2014 – Article created
  • Aug 2016 – Added UFL connector info
  • Jul 2017 – Added adapter options

27 thoughts on “FPV Connectors: SMA, RP-SMA, MMCX, U.FL

  1. Mark

    Is there a connector similar to RP-SMA, but smaller?

    I have an antenna that looks exactly as RP-SMA, but it is only half the diameter

  2. Pravin

    Hello sir,
    Thank you for this article.
    But still, I have a question that, If there was an SMA connector in the market then why they discovered this RP-SMA connector?
    is there any difference between the data rate or in any technical specification? (Other than the physical appearance).

  3. Chris

    I see SMA-K connectors appearing when searching for RMA connectors. Where, if at all, do these come into play in a build?

  4. McB33ZY

    Hey Oscar,
    I have a question about replacing my vtx antenna cable on my Tramp VTX. The stock antenna connector was torn apart after a heavy crash – in order to avoid this in the future, I’m planning to use a 15cm SMA->IPX connector with additional strain relief points on my frame. Is 15cm too long for 5.8 gHz or will my Video Signal still be good?

    1. Oscar Post author

      It’s a shielded wire, as long as you are using good quality wire, 15cm shouldn’t be a problem :)

  5. rinozen

    Hi, how about the pigtail’s cable? Is the black one like in your picture good enough? Or should i buy like in banggood from your link?

  6. Jason

    I have sma connection on my true D and noticed that antenna A the pin hole has gotten a lot bigger than antenna B if the hole is to wide would it make a difference? I’ve been getting really bad performance from my true D and wondered if that could be the reason.

  7. Lacey Lake

    Just saved me from a wrong purchase. I have SMA and not RP-SMA connectors. Here is my rhyme to remember.

    Sma is male and female like you and me.
    RP sma is the opposite you see.

    Some would better understand that RP-SMA is the Transgendered version of SMA without a change in reproductive organs. so, ReProductive (RP) the SAMe (SMA)! This could confuse other even further.

  8. Peter Van Gorp

    Ah, so I can swap a UFL Rp-SMA pigtail with UFL Sma pigtail.. or the other way around. I thought so. Awesome

  9. Patrik

    Hey Oscar.

    I am citing your articles in my final paper I’m doing about (quad)copter Racing. So I just wanted to ask where you source your information form and if there is anywhere I can check those out? They’re really nitpicky about citing and stuff, so while I believe you are a trustworthy source with a lot of knowledge it would still be beneficial to know how you know this stuff.


    1. Oscar Post author

      the info are mostly from what i learned on various forums (probably involves hundreds of posts), and talking to many people in the hobby lol :)
      some info are from wikipedia, so that would probably be the only possible place I can cite

  10. Snebajer1

    So, to remember, SMA is like mainstream sex (no offence intended):
    The female part has a hole and the male part has a pin and wraps around the female.
    Makes sense….

  11. Thai

    Hi Oscar,

    great blog and vids man! Just wondering if you had any signal decrease due to an rp-sma extension cable?


  12. mike

    Sooo… i ordered sma male antenna and my fpv goggle need sma male, can u use the sma male to rp sma female to get a connection, just the stinger right? For that matter put a stinger in the sma female to bridge the connection, hmmmmm

  13. Jesse

    Hi, I like the info but I believe there is a mistake. I work in the plumbing industry and deal with male and female threads all day and I believe you have them mixed up. Short of a lesson in the birds and the bees, but a male thread goes inside a female thead. So the male body has the outside threads and the female has the inside thead.

    1. Oscar Post author

      I don’t think I have. Google image of each thread and you will find they match my description.

      1. Nope

        No, he’s right.


        In mechanical design, the prototypical “male” component is a threaded bolt, but an alignment post, a mounting boss, or a sheet metal tab connector can also be considered as male. Correspondingly, a threaded nut, an alignment hole, a mounting recess, or sheet metal slot connector is considered to be female.

        Male connector pins are often protected by a shell (also called a shroud, surround, or shield), which may envelop the entire female connector when mated. RF connectors often have multiple layers of interlocking shells to properly connect the shields of coaxial and triaxial cable. In such cases, the gender is assigned based on the innermost connecting point.

    2. Nathan

      Hi Oscar.

      The ‘male/female’ of SMA connectors refers to the pin gender, not the thread, so in the case of normal SMA connectors you have it spot on.

      However I’m not sure if RP SMA connector genders are swapped because of this, or if they just keep the gender of their original SMA counterparts.

  14. Daniel

    I believe it was meant as a compliment. As in the only web addresses in his browser history are pages from your incredibly informative site. However I could be wrong.


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