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  • Users: greebling
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  1. greebling

    reflectivity

    Deep inside the water I understand the impeadance is 42 ohms. V pol energy enters the water at 6.4 degrees with an impedance of 377 ohms as the energy penetrates deeper. There must be a transition from 377 to 42 ohms. Any miss match in impedance will cause energy to be reflected. So is the...
  2. greebling

    reflectivity

    Thanks Higgler. Refering back to a previous point of V pol hitting the surface of the sea at an angle of 6.4 degrees where its Z is 377 Ohms, over what distance is the z become 42 Ohms thereby not having a boundry condition, impedance miss match and energy reflected? Or is the energy just...
  3. greebling

    reflectivity

    Thanks Higgler - What happens to the plane of polarisation (V and H) after its has been reflected by the sea?
  4. greebling

    reflectivity

    Many thanks Higgler this is just what I was after. Do you have a reference for the V and H pol Z equations?
  5. greebling

    reflectivity

    I am trying to determine why H pol radars, over a sea path, have a more loby structure than V pol radars. Is it due to different reflectivities of the sea for each plane of polarisation?
  6. greebling

    reflectivity

    could you elaborate on the former please
  7. greebling

    reflectivity

    What is the difference in the reflectivity of the sea for horizontally as opposed to vertically polarised em waves?
  8. greebling

    waveguide beyond cut off

    Consider a pipe of diameter 1.25 lambda and length 10 lambda. At far end of pipe is a larger chamber. At entrance of pipe is a cylindrical blockage approx lambda diameter and lambda long. Will the blockage be sufficient to prevent RF from propogating down the pipe into the larger chamber?
  9. greebling

    canard v rear control surfaces

    What are the advantages / disadvantages of having canard as opposed to rear control surfaces for an aircraft / missile?
  10. greebling

    aerodynamic heating

    Is there a simple formula which will calculate the temperature at the tip of a radome, due to aerodynamic heating, when travelling at supersonic speeds?
  11. greebling

    90 degree hybrid

    how is the 90 degree phase shift achieved?
  12. greebling

    90 degree hybrid

    How does a 90 degree hybrid work?
  13. greebling

    spiral antenna gain

    Thank you photistor, What gain would I expect from a spiral lamba/4 above a cavity as oposed to having an absorbing cavity. Would you expect a cavity to give 3 dB enhancement or 6 dB due to voltage squared being induced for doubling of power due to cavity?
  14. greebling

    polarisation issue

    A horn antenna with its aperture, and launch probe vertical, will produce vertical polarisation (with a small ammount of H pol). However, if the antenna was placed on its back so as to be looking vertically up the launch probe is now horizontal as is its cross pol component. What polarisation...
  15. greebling

    spiral antenna gain

    I was thinking in terms of a cavity 2 * dia, approx Lamda / 4 deep.
  16. greebling

    spiral antenna gain

    How much more gain could I expect to get by placing a spiral above a reflecting cavity as opposed to a cavity backed spiral where the back lobe is absorbed?
  17. greebling

    local oscillator power

    How does local oscillator power effect sensitivity of a receiver?

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