Backgroud 49) The U.S Navy has long proposed the construction of extremely low f
ID: 1431314 • Letter: B
Question
Backgroud
49) The U.S Navy has long proposed the construction of extremely low frequency (ELF waves) communications systems; such waves could penetrate the oceans to reach distant submarines. Calculate the length of a quarter-wavelength antenna for a transmitter generating ELF waves of frequency 75 Hz. How practical is this
61) What are the wavelenght ranges in (a) the AM radio band (540-1 600kHz) and (b) the FM radio band (88-108 MHz)?
QUESTION: Review problems 49 and 61 from your book. You have computed the wavelengths of AM and FM frequency bands. From those calculations, what can you say about the length of antenna's for transmission/receivers of those frequencies?
options:
The length of antennas is independent of the frequency bands of transmission.
FM band transmission does not require antennas -- only AM band does.
AM band reception does not require antennas -- only FM band does.
The length of antennas is related to the power of transmission of the stations and has nothing to do with the frequency bands. The longer the antennas the stronger the source.
The AM band antennas are much longer than the FM band antennas.
The FM band antennas are much longer than the AM band antennas.
The length of antennas is independent of the frequency bands of transmission.
FM band transmission does not require antennas -- only AM band does.
AM band reception does not require antennas -- only FM band does.
The length of antennas is related to the power of transmission of the stations and has nothing to do with the frequency bands. The longer the antennas the stronger the source.
The AM band antennas are much longer than the FM band antennas.
The FM band antennas are much longer than the AM band antennas.
Explanation / Answer
(49) f = c = 3*10 m/s (speed of light)
= Wavelength in meters
f = frequency in Hz
= c/f = 3.0 *10/75 = 4.0 x 106 meters
1/4 of that is 1.0 x 106 meters or 1000 km
(61) for radio waves wavelength lambda = speed of em waves / frequency
then a) for AM band the range is 555.6 m - 187.5 m
b) for FM band the range is 3.41 m - 2.78 m
Question
The length of antennas is related to the power of transmission of the stations and has nothing to do with the frequency bands. The longer the antennas the stronger the source.
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