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52Re: [dxatlas] Newbie questions (tons of them)

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  • Alex, VE3NEA
    Apr 28, 2004

      > 1) What do the light and dark areas mean on the map? Does dark mean
      > that that area on the map is a dead zone? Or does it mean ionization
      > is highest there and thus the best chance of contacting a station?

      If you are talking about the HamCap SNR map, then brighter areas correspond
      to higher SNR.

      > 2) What does SNR mean? What is SNR? Why do I need to know this?
      > How does it affect QSO's?

      SNR is Signal-to-Noise Ratio.

      Three factors affect the availability of the path: 1) MUF. If the MUF is
      below the operating frequency, the path is closed, no matter how much power
      you put in the antenna; 2) path losses. Signal absorption along the path can
      result in a closed path even if the MUF is high enough; 3) noise level. Even
      if the MUF is right and the signal is strong, the path still may be closed
      if the noise in the recipient's area is stronger than your strong signal.
      You can estimate these 3 parameters separately to see if the path is open or
      not, but it is more convenient to just check the predicted SNR, as this
      parameter takes into account all three factors. If the SNR is 3 dB or
      higher, your chances are good.

      > 3) When I move my cursor around the map in DXAtlas, I see the MUF
      > change in HamCAP. Is that the MUF for me trying to reach that
      > location (the location where my cursor is)? Or would I put the
      > cursor over my QTH and go off what it is telling me the MUF is?

      The MUF and other parameters displayed on the status bar in HamCap are for
      the path that starts at your home QTH and ends at the point under the

      > 4) The MUF is the maximum (ie. highest) frequency that, based on the
      > SSN, etc, is best to reach the station?

      Usually the best frequency is about 80% below MUF, but there are exceptions.
      See my answer to question 2.

      > 5) The critical frequency is the highest frequency you can use before
      > the radio waves start going through the ionosphere?


      > 6) How do critical frequency and MUF differ then?

      Critical frequency is just the MUF of a vertical path.

      > 7) From what I understand, you would find a place you would like to
      > work, then find out the MUF and stay below that and the Crit Freq?

      No. You would select the frequency with highest SNR.

      > 8) When I have the 3 apps open at once, there is a little yellow sun-
      > like icon down on the bottom of DXAtlas that displays a number like
      > 8:33-21:15. What does this mean?

      This is the sunrise and sunset time for the point under the mouse cursor.

      73 Alex VE3NEA
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