Modulator plays crucial role in any pulsed grid tube based system. The design of the modulator becomes very crucial when it is employed for airborne applications. This paper describe the design of the low pulse width (approximately 300 ns) floating deck modulator. As this power supply and modulator was to float at high voltage around 40 KV, this development has also involved the selection of insulating material within the restricted weight and volume for airborne applications. To achieve high electrical insulation special potting techniques were used.