I strongly recommend that all anticipating a build of the Kepp design endeavor to obtain or build full-size antennas from the original RCA theremin design. Drawings for the machine work are available on the internet. Thin, telescoping, or stiff "Coathanger" style aerials are a pure waste of time and a sure path to the land of wailing and gnashing teeth. If you want extreme responsiveness with a large playing field (which can be adjusted down to suit your preference), then this is a no brainer. Also, go with the "Concert" and not the "Bass" version of the schematics if you want a large octave range.
Just my 2.439 cents worth.
Fleep
Philip Neidlinger