I know little about this board, although the Interak overview documentation does state that a Tape Interface can be used within an Interak System. Elsewhere, the Interak documentation refers to the board as a "Serial Binary and FM Converter", an indication that it uses frequency modulation to encode/decode a serial stream of binary data.

There is a 1979 Kemitron Electronics booklet “A Guide to SC/MP Programming” that has a description of an assumed earlier but similar TP-A board:

“This board coverts serial binary input data to an audio signal and the converse.” ... “The Kemitron tape board (TP-A) is reasonably sophisticated and uses digital synthesis to produce a near sine-wave output (this is easier to record than a square wave) as well as a majority input gate to reduce the effects of minor tape defects.”