50 Ohm Waterproof BNC Bulkhead Adapter With Dust Cap

For an amateur radio application (7 MHz - 28 MHz) I am seeking a 50 Ohm Waterproof BNC Bulkhead Adapter that I could place through a hole drilled in a Pelican case.

I have located this adapter that looks perfect in every way except that it is 75 Ohm instead of 50 Ohm.

Is anyone aware of something similar at DigitKey for 50-Ohm applications? And if not here… anywhere else?

I love that this one was BNC to BNC so I won’t have to solder or crimp any custom cables inside the box, just a BNC cable from the back of this to the radio.

The documentation on that one states:

50 ohm and 75 ohm BNC connectors will mate with each other.
At frequencies under 10 MHz the impedance mismatch will not have
any affect. If you are above 10 MHz the chances of signal distortion
become more significant.

So it would likely cause problems with my uses on 20-meters (14 MHz) and 10-meters (28 MHz) but would work fine on 40-meters (7 MHz).


The nature of the BNC connector isn’t all that amenable to weatherization, making systems of the sort somewhat uncommon. N or TNC styles are a bit more robust there and may offer a better slate of options. Whether protection in the mated or un-mated condition is of greater interest may also weigh on the matter.

Regarding the impedance mismatch issue, information of the sort referenced is the kind one should take with a (large) grain of salt. Natural phenomena operate on a continuum; “work/no-work” demarcations applied to conveniently-round numbers in that way are a hallmark of loose approximations based on assumption and generalization. A 75 ohm feedthrough in a 50 ohm system will have some adverse effect on performance, it’s simply a question of how much and whether or not it’s tolerable in context. Better to avoid it if possible.

Thank you so much for your reply, I really appreciate the details. I’ll keep looking for options and alternatives, but to answer your question:

I was mostly interested in it being fairly watertight when un-mated. I liked the idea of the screw-on waterproof cover both to keep things dry and almost as importantly, to protect the connector during transport.

Once I select a solution I’ll post my chosen item here just in case it helps anyone else in a similar situation in the future.

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Protective caps for N & TNC are available, with GradConn’s offerings being rated to IP67 when used with their connectors. Depending on what you’re connecting to inside the box, there may even be a cable assembly available, and it looks like customs can be had. Might be worth a look…