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8425Re: [loopantennas] Re: What type of capacitor is used for loop antenna?

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  • Tim Hills
    Apr 2, 2011
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      I did some work with VLF/ELF years ago, 60KHz and down to 6.8 Hz. What I
      found was that below about 20KHz forget about tuned loops. They can be
      built but to get any directional gain they would have to be huge and
      heavy. The more wire used the larger the gauge needed to gain any
      benefit from it. Look up the resistance/Q formulas. Very large
      capacitors (Relative to RF) and electrolytics don't work very well
      either because of the low EMF involved. The best results I got were with
      Tantalum Caps. with a 3V
      bias applied.

      Other than man-made noise there really isn't much in the 1KHz range
      other than produced by thunderstorms and Solar flares. From 70 to 200 HZ
      there's submarine coms. with very slow CW or FSK 5 letter groups, my
      main interest at the time. 6.8Hz is the resonance of the Earth's
      magnetic field, vertical with a capacitance hat, or a big loop laying on
      the ground with low noise audio/instrumentation optimized op-amps with
      filtering/amplification and you can watch it on a scope but it takes
      DAYS to see changes in signal.

      Then again you could mix the 1KHz signal with a 13KHz then use WinRad......

      That Grumpy Old Man..

      On 4/1/2011 19:41, Ray Phillips wrote:
      > Is it possible that you are confusing MHZ (millions of cycles per second) with KHz (thousands of cycles per second)? If you are trying to build a loop to receive MHz transmissions but plugging KHz figures into formulas, then your calculations will be wildly inaccurate.
      >
      > As frequencies fall below 500KHz (0.5MHz) the amount of man-made signals reduce. At 1KHz I would expect all signals to be either natural or man-made noise rather than coherent signals. At 1KHz I, personally, would be using audio techniques not radio techniques. At 1MHz, however, I would definitely use radio techniques such as a loop and capacitor.
      >
      > Don't give up. Let the forum know what signals you are looking for and I am sure you will get help aplenty. If you are definitely looking for VLF signals then there are websites devoted to that pursuit. Take a look at http://www.vlf.it/harald/strangerec.htm or http://abelian.org/vlfrx/ for starters.
      >
      > Ray, vk5ugs
      >
      >
      >
      >
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