Not to usurp Earl's reply but a banjolin would be double strung tuned gdae just like a mandolin or violin.

As an experiment in resonator instrument building, and the start of what I hope will be a longlasting and satisfying hobby I built a resonator mandolin with a pie tin as the resonator, a maple laminated pot encased in a steel body, a maple bridge and neck with a rosewood fingerboard. It sounds surprizingly good considering I got the pie tin for a quarter. I hope to build more instruments - a banjo, a resonator guitar, a harp for my eight-year-old daughter - but I've got a house to finish remodeling first.

PS my wife says she saw Andy Griffeth playing a resonator mandolin on Matlock.