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Microwave Transmission

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  • #38343 Reply
    shamsul haque rubel
    Guest

    why we use in some cases vertical polarization & horizontal polarization.pls answer me

    #38344 Reply
    Alex, South Australia
    Guest

    Hi All,

    some comment about size of the dishes and Space Diversity:

    The limiting factors for choosing size of dishes could be:

     Size of the supporting structure and its current loading level
     The need to design link to a specific reliability parameters (eg 99.999%)
     Certain regulations of Licensing Authorities in a particular country (for instance antenna minimum size and minimum path for certain frequency bands)
     Chosen frequency band – generally on higher bands smaller antennas could be used
     Capacity of the transmission traffic (generally higher capacity links require higher reliability therefore bigger antennas)
     Other factors

    A space diversity technique is used to overcome multi-path propagation issues – eg during abnormal propagation radio rays can be reflected and also bended away from direct path therefore signal loss is present due to this. In simple terms, without going much into theory by having 2 antennas in space diversity configuration, separated say by 15metres, you would have better signal in one antenna, while the other is fading. So the output (resultant of the 2 signals) would be always better than in the situation with the single antenna. Also important that say for a particular case without space diversity you would need say 3m dish to achieve required availability, but if you use 2 x 1.8m space diversity antennas not only you would get better link availability, but also you could spread the loading on the structure more evenly…

    Frequency diversity is using similar principle – when link fades on one particular frequency – you get another frequency as a back up.

    #38345 Reply
    manju
    Guest

    hi in nokia wicrowave, by using flexihopper plus we can increase the capacity to 32e1, how to implement his pls come once say or mail me to m_manju01@hotmail.com

    #38346 Reply
    patrick
    Guest

    You must add PCM card in IDU. And i think also changing ODU.

    #38347 Reply
    john
    Guest

    please can anybody tell me how to trobleshoot microwave links from IDU to ODU?i.e alcatel maicrwave link

    #38348 Reply
    john
    Guest

    Can any give me a difference between SDH and PDH?why do we have these links?where can we use them?if you have notes,website where i can get more knowledge please send to me

    #38349 Reply
    met
    Guest

    hi all,

    could u anyone halp me following question.

    what is patloss?

    BR
    met

    #38350 Reply
    Patrick
    Guest

    JOHN

    I give an explanation down.

    You can also searching on the internet, there are a lot of documents
    ex:
    http://en.wikipedia.org/wiki/SDH

    http://en.wikipedia.org/wiki/Plesiochronous_Digital_Hierarchy

    #38351 Reply
    Patrick
    Guest

    MET

    pathloss:

    I think it is a “line of sight”.

    Line between site A and B.

    #38352 Reply
    AbdulHaq
    Guest

    path loss: In a communication system, the attenuation undergone by an electromagnetic wave in transit between a transmitter and a receiver. Path loss may be due to many effects such as free-space loss, refraction, reflection, aperture-medium coupling loss, and absorption. Path loss is usually expressed in dB.

    This can be calculated from the formula

    Path loss (in dB) = 20 Log (F)+20 Log (D) +32.5

    Where F= frequency in MHz D = distance in Km

    #38353 Reply
    AbdulHaq
    Guest

    shamsul haque rubel

    SHAMSUL HAQUE RUBEL

    why we use in some cases vertical polarization & horizontal polarization.pls answer me

    **********************************

    If you know what polarization means then the following will be helpful in undertsnading the reasons for using H or V polarization:

    Ground-wave transmission is widely used at medium and low frequencies. Horizontal polarization cannot be used at these frequencies because the electric lines of force are parallel to and touch the earth. Since the earth acts as a fairly good conductor at low frequencies, it would short out the horizontal electric lines of force and prevent the radio wave from traveling very far. Vertical electric lines of force, on the other hand, are bothered very little by the earth. Therefore vertical polarization is used for ground-wave transmission, allowing the radio wave to travel a considerable distance along the ground surface with minimum attenuation.

    Sky-wave transmission is used at high frequencies. Either horizontal or vertical polarization can be used with sky-wave transmission because the sky wave arrives at the receiving antenna elliptically polarized. This is the result of the wave traveling obliquely through the Earth’s magnetic field and striking the ionosphere. The radio wave is given a twisting motion as it strikes the ionosphere. Its orientation continues to change because of the unstable nature of the ionosphere. The relative amplitudes and phase differences between the horizontal and vertical components of the received wave also change. Therefore, the transmitting and receiving antennas can be mounted either horizontally or vertically. Although either horizontally or vertically polarized antennas can be used for high frequencies, horizontally polarized antennas have certain advantages and are therefore preferred. One advantage is that vertically polarized interference signals, such as those produced by automobile ignition systems and electrical appliances, are minimized by horizontal polarization. Also, less absorption of radiated energy by buildings or wiring occurs when these antennas are used. Another advantage is that support structures for these antennas are of more convenient size than those for vertically polarized antennas. For frequencies in the vhf or uhf range, either horizontal or vertical polarization is satisfactory. These radio waves travel directly from the transmitting antenna to the receiving antenna without entering the ionosphere. The original polarization produced at the transmitting antenna is maintained throughout the entire travel of the wave to the receiver. Therefore, if a horizontally polarized antenna is used for transmitting, a horizontally polarized antenna must be used for receiving. The requirements would be the same for a vertical transmitting and receiving antenna system. For satellite communications, parallel frequencies can be used without interference by using polarized radiation. The system setup is shown in figure 4-8. One pair of satellite antennas is vertically polarized and another pair is horizontally polarized. Either vertically or horizontally polarized transmissions are received by the respective antenna and retransmitted in the same polarization. For example, transmissions may be made in the 3.7 to 3.74 GHz range on the vertical polarization path and in the 3.72 to 3.76 GHz range on the horizontal polarization path without adjacent frequency (co-channel) interference.

    #38354 Reply
    ivan
    Guest

    hi to all,

    can anyone explain to me the difference between horizontal and vertical polarization? and what to consider what are you goin to choose in designing?

    Thanks!

    #38355 Reply
    Samrat
    Guest

    Hi,
    Can anyone help with the practical significance of these parameters.
    Error Second
    Severly Error Second
    Frequency Synchronization Loss
    Baseband Block Error
    Background Error

    #38356 Reply
    S.H.Rubel
    Guest

    Why we use -48v in telecom sector?
    why not +48v?

    #38357 Reply
    S.H.Rubel
    Guest

    1.What is the difference between PDH & SDH?

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