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  • Q2652

    Q
    The skip zone of HF-transmission will increase when the following change in circumstance occurs:
    A
    Higher frequency and higher position of the reflecting ionospheric layer

    Should the answer not be,

    "Lower frequency and higher position of the reflecting ionospheric layer"

    Thanx in advance,
    Anton

  • #2
    Re: Q2652

    No, the answer is correct.

    Why do you think the opposite?
    Best Regards,

    Tony Pike

    Give Sergei back his dignity......Simples!

    Comment


    • #3
      Re: Q2652

      The higher position of the reflecting layer "yes" because the signal travels further along given a higher reflective layer, but higher frequency means a shorter wavelength, thus a shorter skip distance.

      A lower frequency would give a higher wavelength and thus a greater skip distance.

      Or do I have it wrong?

      Thanx,
      Anton

      Comment


      • #4
        Re: Q2652

        Basically with a higher frequency more and more of the signal escapes the ionospheric layer, so for any of it to be reflected you have to increase the angle (from vertical) to make it reflect off the ionosphere.

        Like UHF and up will hardly have any reflection at all. As you lower the frequency, you will eventually find a frequency that will be reflected at quite a big angle, while low frequencies will be reflected at very low angles (to the vertical), hence the problems with NDBs etc (which operate on low freq).

        That's my take on it, any instructor correct me

        Comment


        • #5
          Re: Q2652

          My version of the notes (Issue 5) says on Radio Navigaion page 2.5:
          The distance from the transmitter to the point where the first returning sky wave is received is called the minimum skip distance. This also decreases with frequency.
          I believe this should say increases with frequency.

          I haven't found any previous reports of this so I thought I'd let you know.
          Last edited by jon h; 18-08-2011, 07:39. Reason: notes are from Radio Nav

          Comment


          • #6
            I also think the answer here should be

            Lower frequency and higher position of the reflecting ionospheric layer....

            The Lower HF bands "come alive" after dark with longer skip distances being obtained.... hence your NDB gets effected at night time and all those MW radio stations from Europe come in on your domestic radio receiver.....

            A quick look at this Ham Radio PDF says a similar thing: http://www.arrl.org/files/file/Techn...df/8501031.pdf (table 1 on the 3rd page)

            Also the IAA Shanwick Atlantic HF operations portrays the same thing:

            https://www.iaa.ie/air-traffic-manag...communications

            Daytime frequencies of 5.5, 8.9 & 13.2MHz i.e. higher during day...
            Nighttime frequencies of 3.4, 5.5 & 8.9MHz .... i.e. lower at night...

            Comment


            • #7
              The answer is correct. It is important to note that the question is asking about skip distance and the part under question is the effect of frequency on skip distance.

              If you use a higher frequency it is more prone to escape out into space; this means the transmissions at a steep angle do escape so do not return to earth. The technical expression for this is to say, with a high frequency the critical angle increases. If the critical angle increases, then the skip distance must increase.

              If I could comment to jon h who was using our books; he quotes, "The distance from the transmitter to the point where the first returning sky wave is received is called the minimum skip distance. This also decreases with frequency." What we mean here is that the skip distance follows the change in frequency, so frequency down - skip distance down, frequency up - skip distance up.

              I hope this helps

              Comment


              • #8
                Originally posted by John CTKI View Post
                If you use a higher frequency it is more prone to escape out into space;
                Hello!
                This means that radio waves in the VHF, UHF and SHF bands are not reflected from the ionosphere and escape into space?And what about the so called Atmospheric Ducting that is described in the notes? Does it depend on the angle of transmission, as you wrote?
                Thanks for your time!

                Comment


                • #9
                  In short, yes. If you have an omni-directional transmission only a part of it would be captured by the atmospheric duct.

                  Comment

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