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Because HF frequencies were being used the power was kept very low to minimize interference to other services during the early tests. At the time of writing it is believed that a full-power relocatable OTHR system situated in Virginia is being used in the anti-drug war. As can be seen from the map this ROTHR can cover a vast area of 1.6 million nautical miles, straddling the whole Caribbean.
And as the parallel rays are merely perpendiculars to the waves which fall on the concave surface, which waves are parallel to AD, it will be found that as they come successively to encounter the surface AB, they form on reflexion folded waves composed of two curves which originate from two opposite evolutions of the parts of the curve AFE. So, taking AD as an incident wave, when the part AG shall have met the surface AI, that is to say when the piece G shall have reached I, it will be the curves HF, FI, generated as evolutes of the curves FA, FE, both beginning at F, which together constitute the propagation of the part AG. And a little afterwards, when the part AK has met the surface AM, the piece K having come to M, then the curves LN, NM, will together constitute the propagation of that part.
Now it must be noted that the same ellipse HME serves to find the refractions of any other ray which may be in the plane through RC and CK. Because every plane, parallel to the straight line HF, or TK, which will touch the spheroid, will touch it in this ellipse, according to the Lemma quoted a little before.
Of course, strong solar activity can virtually make over-the-horizon HF radar unusable. A Spectrum Analyser display shows all the frequencies between 5 and 28 MHz.
"Tell this gentleman what you know of the Bayou Manchac," said Mr. Walker, addressing the negro. "Well, sah!" the darky replied, "I jus hab looked at yer boat. Four ob us can hf him ober de levee, an' put him on de cart. Den wees mus done cart him FOURTEEN miles 'long de Bayou Manchac to get to whar de warter is plenty fur him to float in.
And, therefore, the time of the light along HF, supposing that the ray had been OF, would be equal to the time along BG in the interior of the medium C. But the time along AB is equal to the time along OH; therefore the time along OF is equal to the time along AB, BG. Again the time along FC is greater than that along GC; then the time along OFC will be longer than that along ABC. But AF is longer than OF, then the time along AFC will by just so much more exceed the time along ABC.
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I found then that always, when the inclinations of two rays which come from opposite sides, as VK, SK here, are equal, their refractions KX and KT meet the bottom line HF in such wise that points X and T are equally distant from the point M, where the refraction of the perpendicular ray IK falls; and this occurs also for refractions in other sections of this Crystal.
Since then the angle HBF is equal to PBA, and the angle BFG equal to QBC, it follows that the sine of the angle HBF will also have the same ratio to the sine of BFG, as the velocity of light in the medium A is to its velocity in the medium C. But these sines are the straight lines HF, BG, if we take BF as the semi-diameter of a circle.