6. Required Power Gain is graphed in this display, for 50% reliability. The middle curve is the same as that of the SNR display and shows the coverage limits at 0 dB added power gain. Power gain is the sum of the transmitter output power plus the gain of the circuit antennas, diminished by any transmission line and/or matching circuit loss. The other two curves are for power gains of plus and minus 10 dB with respect to the center curve. The red curve defines the further limits of areas that could be covered if 10 dB of transmitter power or antenna gain could be added, and the area gained is shaded red. The green curve shows the smaller coverage area that would result if the combined power gain of the transmitter or antennas was reduced by 10 dB. These displays are useful for planning station design modifications. For example, the effects of changing from a simple horizontal dipole antenna to a directional beam with significant additional gain can be seen at a glance in the Required Power Gain coverage displays.