Binary phase shift key modulator with programmable level control

A BPSK modulator for modulating a data signal onto a carrier signal comprises first and second transistors connected in a mirror configuration and a center tap transformer. The collectors of the first and second transistors are coupled to a first winding of the center tap transformer and the BPSK modulated carrier signal is provided at the output of the transformer. Unmodulated data is input to each of the bases of the first and second transistors. The emitters of the first and second transistors are coupled to the collector of a third transistor whose base receives the carrier signal. A programmable gain control circuit is also coupled to the base of the third transistor for step-wise adjustment of the transmit level of the BPSK modulated carrier signal. In this manner, the transmit output level of the modulator may be adjusted when necessary in the event of changing environmental or other considerations.