Loop Antenna Connector

Problem

We sometimes use a loop antenna for EMI investigation. One of these antennas is older than me and the BNC connector tip pulled out of the connector when unplugging the antenna. The solder joint had snapped where the conductor joined to the centre contact.

Diagnosis

Unfortunately, the BNC connector shell was screwed onto the body of the antenna and covered with a plastic dip coating. We had to cut away a band of the coating and peel it away from the connector. The connector was clearly threadlocked or glued in place. We decided to try heating the connector to release the thread-lock. Using a damp rag to protect the antenna body from the heat and the vice jaws holding it, we pointed a blowtorch at the connector shell for a few seconds.

Solution

After a couple of tentative cycles of heating and testing whether it would unscrew, the connector came unstuck and easily unscrewed. Due to the construction of the antenna, the centre contact is poorly supported and the solder joint is a mechanical fixing as well as electrical. We were then able to re-solder the centre contact and reassemble the connector, this time without threadlock for the next time we inevitably need to look at it.

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