I have a length of RG-316 single shield 50Ω coaxial cable carrying a 5.8 GHz signal that I need to connect to a PCB. While cheap relative to most coaxial connectors, SMA connectors are still quite expensive, take up space and are relatively heavy. The PCB was designed for side mount SMA connectors.
- Could I replace the original SMA connectors with direct soldering joints like this, without causing a large impedance mismatch?
How could I improve the RF performance of the connection?
The mechanical strength of the joint is poor, and the teflon insulator does not bond well with common adhesives. Can I protect the joint with nonconductive adhesives (epoxy, hot glue) without significantly affecting its RF performance? What would be the best way to secure it mechanically?
Answer
Soldering directly to the pads of the SMA connector instead of using SMA connectors should work fine electrically.
The obvious problem is that the cable is no longer removable. If you're fine with that, then go ahead.
It would be good to have some mechanical strain relief if this has a chance of getting flexed. At only 2 inches wavelength, you do need to be careful about impedance changes over only a few mm. I'd stay away from adding any material around the solder joint or the wires outside the shield. However, you can do most anything you want back down the cable a bit from the solder joint and where the shield is still intact. Perhaps you can hold the cable down with cable ties or something further from the board.
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