Radar System Engineering

386 THE MAGNETRO.V AND THE PULSER [SEC. 10.11
in rate of rise or in flatness of top. Wider-range transformers will be
practical only when higher permeability cores and stronger insulation
with lower dielectric constants are available.
Insulation between windings and adequate cooling must also be taken
into account in design. High-power transformers lend themselves most
readily to oil insulation because of the insulating and convection-cooling
properties of the oil. In the lower-power range (200 kw and down) it is
usually convenient to use solid dielectric materials, with a consequent
saving in weight and size. Figure 10.46 shows the variation in size of a
pulse transformer with power output. As in the case of pulse networks,
FIG. 10.46.—Pulse transformers,
the size and weight of a pulse transformer depends not only upon the
pulse power to be handled, but also upon the~ulse length and the repetition
rate. These, together with the transformer efficiency, determine the
amount of average power which must be dksipated by the transformer.
A pulse transformer contributes a certain amount of undesirable
inductance and capacity to the pulser circuit. Special damping devices
may be necessary to remove unwanted oscillations. Damping resistors
and appropriately phased diodes are ordinarily used for this purpose.
Pulse Cables.—In handling high-power pulses with steep wave fronts,
extreme care must be taken to shield the equipment sufficiently to prevent
the radiation of signals which interfere with the operation of communications
receivers and other electronic equipment. This shielding is espe.
cially necessary when the pulse must be transmitted several yards between
pulser and load. Existing pulse transmission cables and their connectors
provide satisfactory shielding and resistance to voltage breakdown, but
are still rather bulky, hard to assemble, and heavy. Considerable
improvement in their detailed design can be hoped for.