A new class of microwave comb generator featuring formerly unattainable output power levels, low jitter, and spectral content programmability has been introduced. Based on a custom ultra-high-repetition-rate GaN differential pulser IC, the palm-sized Ultracomb-8G is powered from any USB3.0/3.1 port through which the user can program comb amplitude, comb picket spacing, and low/high-frequency spectral weighting. Comb picket spacing can be software-programmed to any frequency from 10 MHz to 2 GHz in single-ended-output mode (10 to 50 MHz in differential output mode) in 0.01 Hz steps, generated by an on-board LMX2594 synthesizer driven from an internal 150fs-jitter reference clock or external 10 to 500 MHz reference. The unit can also be programmed in 1:1 clock mode, enabling the pulse repetition of the comb generator (and the comb tooth spacing) to be the same as the external reference/clock input. Its differential outputs enable direct antenna connections without the use of a BALUN and 3 dB higher total output level.