Plat earth effect of a typical antenna is 25dB to 45dB over an isotropic antenna, depending on the size of the antenna and the operating frequency. Thus with reasonable transmitter power and receiver Straight ray sensitivity, satisfactory transmission may be achieved. We may now determine the signal at the microwave receiver input for a typical path. Figure 50.9 is a graphical representation of the factors to be considered in this calculation. At the left side of the Flat earth figure, the transmitter output power is shown. The loss of the transmission line is shown as a decreasing signal between the transmitter output and the input to the antenna. The antenna pro- Figure 50.8 Three methods of drawing path profiles vides a gain, shown as a signal increase. The path loss, representing the largest single contributor, is shown as a decreasing signal as the path is traversed. represent each curvature or use of a curved template to draw the path line over a flat earth base line are two methods. With the advent of the modern scientific calculator, the easiest method is to use a Transmit antenna Receive antenna straight earth line and a straight path line with the necessary clear- ance over each obstruction calculated and shown by a symbol. Both Waveguide the earth curvature and the desired Fresnel clearance must be calcu- lated and added in order to plot the clearance target above each obstruction. Transmitter Receiver 50.1.3 Field path survey Transmitter Free space loss In most cases, the path design derived from the map study must be antenna gain Receiver confirmed by a field survey. Investigation of the potential micro- antenna gain wave sites is usually necessary, and information on man-made obstructions as well as confirmation of natural obstructions should Transmitter Receiver waveguide loss be obtained. Potential reflection points may also be determined. waveguide loss A microwave path designed and installed without the benefit of a Transmitter power Received signal field survey is a high risk except for the obv