Equalized Delay Lines

An improved design of signal delay lines is discussed in which phase distortion is held within the narrow limits required. The decrease of time delay at higher frequencies due to decrease of effective inductivity is compensated by a rise in effective capacitance due to distributed bridge capacities. In some high-impedance lines the natural coil capacitance will sufflice for this compensation; in other cases a controlled amount of bridge capacitance is introduced by means of floating patches of metal foil along the coiled conductor, insulated from it, from each other, and from ground. Echoes, due to mismatch of the lines at high frequencies, may be suppressed by dividing the winding into sections, each too short to yield an echo component within the transmitted frequency range. The design of typical delay lines for 400, 1000, and 3000 ohms impedance is discussed and their delay, attenuation, and impedance characteristics are shown. A delay line with lumped iron-dust cores is described. A practical design is presented for the lumped-parameter low-pass filter m= 1.27, as used for delay lines with very low impedance and for very high voltages.