Application Note

Is It Safe To Mate SMA And 2.92mm Connectors?

By Brian Baxter

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Is it safe to mate SMA and 2.92mm Connectors?

This question comes up frequently enough that I thought I’d write a short article on it. The short answer is, maybe. At Marki, we generally treat SMA and 2.92mm (K-Type) connectors as mating connector types. However, there are a number of reasons why you should use caution when mating SMA and 2.92mm connector types.

To understand where the issues are, we need to take a look at the mechanical specifications for these different connectors. These specifications can be found in MIL-STD-348B, a military specification document created and maintained by the United States Defense Logistics Agency for the purpose of “standardizing Radio Frequency connector interfaces”.

We will reference the following figures in MIL-STD-348B:

Figure 310-1 contains drawings and dimensions defining the SMA pin contact interface.

Figure 310-2 contains drawings and dimensions defining the SMA socket contact interface.

Figure 323-1 contains drawings and dimensions defining the SMK pin contact interface.

Figure 323-2 contains drawings and dimensions defining the SMK socket contact interface.

Now, lets look at some of the differences between the SMA and 2.92mm connector types:

  • 1) SMA connector pins are allowed by MIL-STD-348 to be slightly longer than K-type. (See 310-1 dimension H vs. 323-1 dimension E) If these longer pins become damaged or are not installed perfectly straight, they can more easily damage the fragile 3.5 and 2.92mm sockets. This is especially true if the pin side is “accidentally” rotated while connecting.
  • 2) SMA connectors are often manufactured to lower tolerances and as such you are more likely to encounter SMA parts that are at the EDGE of MIL-STD-348 tolerance (being generous here). This could exacerbate the above pin length issue and result in socket damage to 2.92mm connectors.
  • 3) Note that the 3.5 and 2.92mm use an air dielectric around their sockets. SMA connectors use a solid PTFE (Teflon) dielectric per MIL-PRF-39012. Again, related to the extended pin length of the SMA, repeated insertions of the SMA pin into a 3.5 or 2.92mm socket are more likely to deform the socket over time vs that of an SMA socket having a solid PTFE dielectric insert.

The above notwithstanding, Marki treats SMA and 2.92mm connectors as mating connectors.

We are regularly asked about swapping connectors on our modules. As a rule, we don’t do connector swaps for mating connectors with LOWER frequency performance. (i.e. swapping out a 2.92mm for an SMA). However, we will swap to HIGHER frequency connectors and also perform a sex change as required.

Connector changes are considered custom parts and should be requested through the following request-for-quote link at https://markimicrowave.com/company/rfq/. We will post a detailed example of how to request a custom connector configuration in an upcoming Tech Note. In the meantime, if you have any questions, please contact support@markimicrowave.com for assistance.

Marki Microwave