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Q&A

Discussion in 'General CB Services Discussion' started by C2, Mar 19, 2007.

  1. C2

    C2 Sr. Member

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    I would like to know what happens with a capacitor after its series resonance. Could it still be used as a DC block in an amplifier beyond its series resonance?


     

  2. Hamin' X

    Hamin' X Active Member

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    I assume that you mean the "series resonant frequency"?

    Yes, the capacitor will still block DC, up to it's rated voltage.

    Resonance has to do with the point at which the reactance of the capacitor and the inductor that it is in series with, cancel each other out and reach an effective impedance of zero. It only occurs in AC circuits.

    Rich
     
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    It will still block DC but it will start to appear as an inductor to the AC in the circuit it is in.
     
  4. C2

    C2 Sr. Member

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    I was told you could not use it as a DC block above its series resonant freq.


    New question:

    Q: What is a loop antenna?

    -A large circularly-polarized antenna
    -A small coil of wire tightly wound around a toroidal ferrite core
    -Several turns of wire wound in the shape of a large open coil
    -Any antenna coupled to a feed line through an inductive loop of wire
     
  5. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Is this a test?

    What is a loop and why use it?
    1). A loop antenna is a small multi turn loop of less than 1/10th wavelength in length. The loop is wound on a form, which may be either box (solenoid), or spiral (pancake) wound. The core material can either be air, or a powdered iron compound (Ferrite). The gain of a loop is much less than a longwire, but it has much less noise pickup. A properly designed Loop primarily responds to the magnetic component of the radio wave. Note that noise resides primarily in the electrical component. A vertical antenna responds mainly to the electrical component.

    The above was from Here
     
  6. C2

    C2 Sr. Member

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    That appears to be so, but then why do we have terms like delta loop and the like?

    So that HF slinky thing is really a loop antenna and that long wire that I form into a rectangle, or whatever shape, is not really a loop antenna? Am I just missing the "full wave" part of loop antenna?
     
  7. C2

    C2 Sr. Member

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    One other thing, when I was making a helical antenna for GPS, I figured it was somewhat like an array of full-wave loops, at least the circumference was near 1-wl long.

    And why not call it a helicoil antenna?
     
  8. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    The slinky is not a loop antenna. Neither is the helical antenna.A loop radiates in a plane perpendicular to the plane of the antenna.A helical antenna like you built for GPS is actually a helix and radiates off the end.A loop must have both ends connected to the feedline and fully enclose space. I thought you were talking in general terms about what a loop antenna is.If you take anything and form a circle or other reasonably regular polygon then one could say you have formed a loop. If it is wire and connected to a RX/TX then it becomes an antenna hence a loop antenna. A delta loop is so named because it is shaped like the Greek letter Delta,a triangle.

    Now how badly did I explain that one? :? :LOL:
     
  9. C2

    C2 Sr. Member

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    well, for the test question above, which would you pick, since none of them seem entirely correct?
     
  10. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    You tell me. I already passed my tests a long time ago. :LOL: None may seem 100% correct but by process of elimination you can easily rule out three of them. ;)

    1- Does a loop antenna HAVE to be circularly polarised?

    2-Does a loop antenna HAVE to have a ferrite toroid core?

    3- Is just any type of antenna a loop antenna simply because it is connected to a feedline by an inductor? I'm picturing a 1/2 wave vertical with a link coupler BTW :? ;)
     
  11. C2

    C2 Sr. Member

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    Yes, I passed it too, once. And I'll do it again. I just found that interesting.
     
  12. Moleculo

    Moleculo Administrator
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    That question is from the FCC Extra pool. The answer they're looking for is C
     
  13. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    That's why I did not discount that one. ;)
     
  14. C2

    C2 Sr. Member

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    yes, even though it meets the same criteria as your number 2.

    Does a loop antenna HAVE to have a ferrite toroid core--no!

    Does a loop antenna HAVE to have several turns of wire and be wound in the shape of a large open coil?

    What am I missing? The correct answer seems closer to the definition of an inductor than the previous wrong answer.

    But, oh well.

    :D
     
  15. Moleculo

    Moleculo Administrator
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    Something I had to learn a long time ago in college: Learn how to take the test; don't just learn the material they're teaching. Often the exercise of taking tests is learning more about what they're getting at, or learning what they're looking for than it is to actually understand every right / wrong answer scenario.
     

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