What is the relation of distance of propagation of EM wave and operating frequency?

as we known that frequency is directly proportional to distance each other but we consider an example, AM operates with low frequency range when compared with WiFi frequency but it is operated at larger distances. how it happens?

Replies

  • Ramani Aswath
    Ramani Aswath
    Praveen Kantipudi
    as we known that frequency is directly proportional to distance each other
    What has distance to do with frequency?

    This tutorial may be of help:
    #-Link-Snipped-#

    This video explains the process of propagation:
  • Jeffrey Arulraj
    Jeffrey Arulraj
    Praveen Kantipudi
    as we known that frequency is directly proportional to distance each other but we consider an example, AM operates with low frequency range when compared with WiFi frequency but it is operated at larger distances. how it happens?
    Frequency is not proportional to distance.

    Frequency is related to velocity of a signal only
    WiFi signals are meant only for short range and this is done by deliberately limiting the power of the signal.

    Check the power of the signals here in the link dBm - Wikipedia

    The Wattage of Wifi is no way comparable to that of AM signals. That is why we have lesser range for WiFi than AM.

    If we use the same Voltage and Current (Electric Field and Magnetic field Intensities) ratings which we use for AM signals, WiFi will be a lot stronger and can travel a longer distance than AM.
  • Shashank Moghe
    Shashank Moghe
    Jeffrey Samuel
    Frequency is related to speed and velocity of a signal only
    Speed AND velocity? Please explain that. I think signals are emitted isotropically. What has velocity got to do with frequency? I think speed is enough.
  • Jeffrey Arulraj
    Jeffrey Arulraj
    Sorry about that error and thanks for pointing it out. #-Link-Snipped-#

    RF sources are ideally isotrophic But they have directional nature. So its better to stick to Velocity than speed here
  • Shashank Moghe
    Shashank Moghe
    By having a directional nature, do you mean the "waves" by themselves have a directional nature? I know little about EM, but still unable to understand the relation between velocity and frequency. Do we have a formula that relates the two?
  • Ramani Aswath
    Ramani Aswath
    Shashank Moghe
    velocity and frequency
    In vacuum, irrespective of frequency all EM radiations have the same velocity - c.
    Unless the source is a collimated one (like a LASER), all waves are emitted spherically (in all directions).

  • Shashank Moghe
    Shashank Moghe
    A.V.Ramani
    In vacuum, irrespective of frequency all EM radiations have the same velocity - c.
    Unless the source is a collimated one (like a LASER), all waves are emitted spherically (in all directions).

    Exactly my point when I said "isotropically". And I just didnt mean EM waves, but waves in general, hence refrained from limiting the 'speed' to 'c'. So, coming back to the orihinal question, what frequency has to do with velocity?
  • Ramani Aswath
    Ramani Aswath
    Shashank Moghe
    what frequency has to do with velocity
    As Shakespeare says,"None, Brutus, none."
    As an aside, in still water a pebble dropped will set up concentric ripples. However, in the sea the waves are in one direction.
  • Shashank Moghe
    Shashank Moghe
    A.V.Ramani
    However, in the sea the waves are in one direction.
    It might appear the waves are in one direction because the sampling set for a human being is a very small length of the sea shore. It can be said that the wave-front is so large in diameter, any small section of the front appears to be a straight line. In other words, if you dropped the island of Manhattan from a considerable height in a still Arabian Sea, midway between the African continent and the Indian subcontinent, a person observing the waves on the Alibaug beach will still say they are in one direction. So will a person on a shore in Mauritius.
  • Ramani Aswath
    Ramani Aswath
    Not quite. These waves are generated by the wind, which has a broad front. So they can be unidirectional.
  • Shashank Moghe
    Shashank Moghe
    Well, I believed that waves are created by the underwater movement (which makes them isotropic) and that effect is just magnified by the wind. I did not know that waves are a purely wind-induced phenomenon. Early morning eye-opener!
  • Ramani Aswath
    Ramani Aswath
    Shashank Moghe
    waves are created by the underwater movement
    You are right in case of underwater seismic activity causing Tsunamis. These will of course radiate from the epicenter of the disturbance much like dropping Manhattan on the ocean.
  • Jeffrey Arulraj
    Jeffrey Arulraj
    Frequency = Velocity / Wavelength

    F=c/Lambda

    EM waves have some specific modes of propagation TE TM and TEM. These are also hindered by the Antenna used to radiate them into the atmosphere mate
  • Shashank Moghe
    Shashank Moghe
    When you replace Velocity by "c", it implies you are talking about speed. Not velocity, but just the magnitude of velocity.
  • Jeffrey Arulraj
    Jeffrey Arulraj
    Velocity is not always c mate. Only in free space we have speed of light as c

    Generally we write Velocity as
    V=c/sqrt(K)

    Where K = dielectric constants
    k=ur*er
    In vaccum we have K=1 so v=c
    ur(read as mu suffix r)= Relative permeability of the material
    er( read as epsilon suffix r)= Relative permittivity of the medium

    This is the actual equation for velocity of EM

    In different dielectrics and conductors the velocity becomes a complex term depending on the dimensions of the material. Pls google Velocity of EM in Cylindrical or circular wave guide that will give you a small idea
  • Shashank Moghe
    Shashank Moghe
    You are right about the formula for V here. That is not what I am questioning at all. All I am saying is that for frequency measurement, why do you use velocity when all you take into consideration is speed. Where does the directional nature of waves come into picture for calculation of frequency?
  • n1kh1l
    n1kh1l
    Shashank Moghe
    Well, I believed that waves are created by the underwater movement (which makes them isotropic) and that effect is just magnified by the wind. I did not know that waves are a purely wind-induced phenomenon. Early morning eye-opener!
    Hi
    I think waves are result of gravitational attraction of sun and moon. Underwater movements will give rise to swell. ( or is it tides that are result of gravitational pull. confused)
    My thinking. May be wrong. And sorry for diverting from main topic.
    About the main topic I would like to add something.
    US and USSR during cold war had developed a transmitter system to "talk" with their submarines. The transmitter used to transmit in long wavelength of several meters and very low frequency (in Hz) but the speed of propagation was slow. This transmission was done under water and not in atmosphere and the power required for it was enormous.
  • Praveen Kantipudi
    Praveen Kantipudi
    thanks sir , to give clarity on mode of propagation.
  • Praveen Kantipudi
    Praveen Kantipudi
    thanks for clarifying doubt.
  • Praveen Kantipudi
    Praveen Kantipudi
    Micro Strip transmission line is the one the feed element to micro strip patch antenna. As my knowledge is concern, the strip line which is feed to patch is not responsible for radiation where radiating slots of patch element the commonly radiate.
    And my question is it a true? if it is why? or if not why?

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