is: Where is the resistance per unit length, is the inductance per unit length, is the conductance per unit length of the dielectric, is the capacitance per unit length, and is the frequency. The "per unit length" dimensions cancel out in the impedance formula. At DC the two reactive terms are zero, so the impedance is real-valued, and is extremely high. It looks like . With increasing frequency, the reactive components take effect and the impedance of the line is complex-valued. At very low frequencies (audio range, of interest to telephone systems) is typically much smaller than , so the impedance at low frequencies is , which has a phase value of -45 degrees. At higher frequencies, the reactive terms usually dominate and , and the cable impedance again becomes real-valued. That value is , the characteristic impedance of the cable: . Assuming the dielectric properties of the material inside the cable do not vary appreciably over the operating range of the cable, the characteristic impedance is frequency independent above about five times the shield cutoff frequency. For typical coaxial cables, the shield cutoff frequency is 600 (RG-6A) to 2,000 Hz (RG-58C). The parameters and are determined from the ratio of the inner () and outer () diameters and the dielectric constant (). The characteristic impedance is given by Attenuation (loss) per unit length, in decibels per meter. This is dependent on the loss in the dielectric material filling the cable, and resistive losses in the center conductor and outer shield. These losses are frequency dependent, the losses becoming higher as the frequency increases. Skin effect losses in the conductors can be reduced by increasing the diameter of the cable. A cable with twice the diameter will have half the skin effect resistance. Ignoring dielectric and other losses, the larger cable would halve the dB/meter loss. In designing a system, engineers consider not only the loss in the cable but also the loss in the connectors. Velocity of propagation, in meters per second. The velocity of propagation depends on the dielectric constant and permeability (which is usually 1). Single-mode band. In coaxial cable, the dominant mode (the mode with the lowest cutoff frequency) is the TEM mode, which has a cutoff frequency of zero; it propagates all the way down to DC. The mode with the next lowest cutoff is the TE11 mode. This mode has one 'wave' (two reversals