To answer your questions,
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Apparently this is called an “M4 70 Pitch” connector.
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According to Dakota Alert, this is a proprietary connector that they chose when they originally designed the M528-HT and as far as they know there is no antenna or adapter on the market that will fit it other than the one included with the radio.
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The Wouxun KG-805M is a powerful MURS radio that is loaded with features, including channel scan, CTCSS tones/DCS codes and customizable channels. It’s part of the KG-805 series, so the battery, charger and other accessories for the KG-805F FRS and KG-805G GMRS versions are fully compatible with it. We have a video on it in the forum as well. Plus, it’s $5 less than the M538-HT.
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The short answer is, I wouldn’t try a BNC adapter on it. I’ve been told some hams have modified the M538-HT by replacing the factory installed connector and soldering in a BNC or SMA connector, but I wouldn’t recommend this either myself.