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7370Re: [loopantennas] Loop Capacitance

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  • richard
    Apr 1, 2010
    • 0 Attachment
      On Thu, 01 Apr 2010 07:11:43 -0000
      "ozzy_1kw" <ozzy_1kw@...> wrote:

      >
      >
      > If the tuning is done by the small loop for best swr then for a single band hf cb i can put the
      > exact capacitance required or is the tuning too sharp to cover the entire cb band??
      >
      > what is the purpose for the variable capacitor ,is it multiband usage ?
      >
      > TY Rob
      >
      >
      > PS, i see on youtube the guy that sells loops.his appear to be upside down with the tuning
      > capacitor on the bottom that he tunes with his thumb. is there any issues feeding it from the top
      > and running the coax down the side of the loop ?
      >
      > Cheers Rob
      >
      Rob
      If you would bother to use the spreadsheet program of OH7SV, you would see that on a loop diameter
      roughly the same as a bike wheel, the 3dB point is about 50 KHz, whats that 4 CB channels ?

      Come on you should know that you will never learn anything if you don't try.
      Use the spreadsheet that I've now sent you twice.
      All you have to do is alter the value in the left hand column, that's frequency , length of the
      loop, the conductor diameter( how thick it is) and how much power you are going to put in it.

      Results
      Inductance (uH) 1.580
      Capacitance (pF) 21.2
      XL = XC (ohms) 273.0
      Distributed C (pF) 5.4
      Tuning capacitance (pF) 15.8
      Main loop diameter (m) 0.637
      Feeding loop diameter (m) 0.127
      Radiation resistance (ohms) 0.227
      Loss resistance (ohms) 0.067
      Parallel resistance (kohms) 127
      Efficiency (%) 77.2
      Compared to ideal loop (dB) -1.12
      Loaded Q 465
      Bandwidth -3dB (kHz) 59.2
      Capcitor rms voltage (V) 2519

      Thats what you get roughly for what you are using.

      If you can't get enough decimal places in the left hand column you can change the cell properties,
      details of how to do this are in the "help" column in EXCEL and Open office.

      If you really want to become a Ham you will have to learn some basic theory
      Google is your friend.
      If you go to your local club you will probably get given a ARRL or RSGB Handbook where someone has
      bought a new one , and doesn't want the old one.
      The process of learning is not asking questions to which you have already been given the answer.
      but being able to understand what's in front of you.









      --
      Best wishes

      Richard Bown

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