Eirp 1
MBC transmission loss Receiver antenna gain
occurring, of course, toward the end of a trail's useful life. Coding with appropriate interleaving is one method of mitigating these multipath effects.
D-layer absorption often is neglected in link budget analyses of meteor burst links. We discuss D-layer absorption and its calculation in Chapter 12. Another source is CCIR Rep. 252-2 (Ref. 10). D-layer absorption, a daytime-only phenomenon, may exceed 3 dB at 40 MHz at midlatitudes during comparatively high sunspot number periods. It is about half this value at 60 MHz.
Yet another path loss is due to Faraday rotation. The D region and the earth's magnetic field cause a linearly polarized very high frequency (VHF) wave to be rotated both before and after meteor trail reflection. These rotations result in an overall end-to-end loss due to polarization mismatching between an incident wave and a linearly polarized receiving antenna. An excellent paper dealing with Faraday rotation effects on meteor burst communication links was published by Cannon in 1985 (Ref. 11).
As in the case of D-layer absorption, polarization rotation loss is also affected by path length (secant of the takeoff angle), the sun's zenith angle, and the sunspot number. Like D-layer absorption, Faraday rotation losses also disappear at night. Faraday rotation losses decrease rapidly as frequency increases. Cannon (Ref. 11) shows Faraday rotation losses varying from 1 dB to over 15 dB at 40 MHz (very path dependent) and dropping to a maximum of 1.6 dB at 60 MHz on the same paths.
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