I dont know if this link is to a legal copy of Practical Radio-Frequency Handbook by I Hickman.. But this is a great PDF book - have a look at it before you buy a copy (I have a genuine copy bought in 2004)
It can be a bit heavy, and most of the RF subjects are about RF - Theremins are almost operating at audio ;-) ... Nonetheless, extremely useful topics relevant to Theremins are discussed... But dont get misled by the Antenna theory - Almost none of this applies to Theremins, where the "antennas" are 99.99999% simply capacitive sensors.
Radio-Frequency Handbook by I Hickman (http://zone-gnostik.org/bd/Sciences-Arts-Conscience/Electronics/Collection/HICKMAN,%20I.%20(2002).%20Practical%20Radio-Frequency%20Handbook%20(3rd%20ed.).pdf)
It can be a bit heavy, and most of the RF subjects are about RF - Theremins are almost operating at audio ;-) ... Nonetheless, extremely useful topics relevant to Theremins are discussed... But dont get misled by the Antenna theory - Almost none of this applies to Theremins, where the "antennas" are 99.99999% simply capacitive sensors.
Radio-Frequency Handbook by I Hickman (http://zone-gnostik.org/bd/Sciences-Arts-Conscience/Electronics/Collection/HICKMAN,%20I.%20(2002).%20Practical%20Radio-Frequency%20Handbook%20(3rd%20ed.).pdf)