A choke is the cocktail weenie-looking thing that surrounds an electrical supply wire near the device end. It magically captures stray emissions, and many power supplies come with them. I ended up with 3, so I put one on the wire that comes from the little iFly battery to the 740, and I put two on the power supply that comes from the cigarette plug to the iFly battery. I'm sure two is overkill but the extra one would've lived its entire life in the back of a drawer.
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