Question
Define critical frequency denoted by $f_c$, maximum usable frequency denoted by MUF in vertical radiation, and inclined radiation and specify their equations.
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The critical frequency is the highest frequency that can be reflected back to Earth when a radio wave is transmitted vertically (at 90° to the Earth's surface) toward the ionosphere. Show more…
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If the critical frequency is 10 kHz in sky wave propagation, what is the best critical frequency to use assuming a 30° radiation frequency angle?
35.18. An FM radio station has a frequency of 107.9 $\mathrm{MHz}$ and uses two identical antennas mounted at the same elevation, 12.0 $\mathrm{m}$ apart. The antennas radiate in phase. The resulting radiation pattern has a maximum intensity along a horizontal line perpendicular to the line joining the antennas and midway between them. Assume that the intensity is observed at distances from the antennas that are much greater than 12.0 $\mathrm{m}$ (a) At which other angles (measured from the line of maximum intensity) is the intensity maximum? (b) At which angles is it zero?
DATA Short-wave radio antennas $A$ and $B$ are connected to the same transmitter and emit coherent waves in phase and with the same frequency $f$. You must determine the value of $f$ and the placement of the antennas that produce a maximum intensity through constructive interference at a receiving antenna that is located at point $P,$ which is at the corner of your garage. First you place antenna $A$ at a point $240.0 \mathrm{~m}$ due east of $P$. Next you place antenna $B$ on the line that connects $A$ and $P$, a distance $x$ due east of $P$, where $x<240.0 \mathrm{~m}$. Then you measure that a maximum in the total intensity from the two antennas occurs when $x=210.0 \mathrm{~m}, 216.0 \mathrm{~m},$ and $222.0 \mathrm{~m}$. You don't investigate smaller or larger values of $x$. (Treat the antennas as point sources.) (a) What is the frequency $f$ of the waves that are emitted by the antennas? (b) What is the greatest value of $x$, with $x<240.0 \mathrm{~m}$, for which the interference at $P$ is destructive?
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