Ham Radio - The Chameleon Antennas power compensator for magnetic loops.

Discussion in 'Amateur Radio News' started by KB7TBT, Nov 3, 2019.

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  1. KR3DX

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    It's simple. No need to spend 15 minutes watching a video. To make a small antenna as efficient as possible, you want to make the current as uniform as possible over the length of the antenna by using as much capacitance as possible at the ends of the antenna. That's all that this "power compensator" (their name for a capacitor) is doing. You want to use an antenna that is physically small compared to the wavelength only when you have no other choice. It's a little bit better than a leaky dummy load.
     
  2. PA0MHS

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    That would be true for the capacitor between the ends of a loop. This capacitor is only connected to one end of the loop and not even used as a capacitor because the other endof the capacitor is not connected to anything. So this capacitor does nothing as a capacitor. It's just a parasitic "load" on one end of the loop, thus lowering the Q. And that will also lower the current through the loop and the voltage across the tuning capacitor, allowing more power to be input to bring the radiated power to the same level as without the "power compensator". This is just a fake product, sold to make money and to make you feel good.
     
    VE3VXO likes this.
  3. KR3DX

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    There is no PHYSICAL connection, but the other plate of the capacitor DOES couple to the loop and affect its performance. Otherwise, I agree with you completely. W8JI has a very good explaination of "magnetic loops" on his website: https://www.w8ji.com/magnetic_receiving_loops.htm
     
  4. PA0MHS

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    That is exactly what I meant with "It's just a parasitic "load" on one end of the loop". If this device had been a metal disc, it would have had the exact same effect.
     
  5. KR3DX

    KR3DX Subscriber QRZ Page

    I agree completely
     
  6. AA6RE

    AA6RE XML Subscriber QRZ Page

    So far it looks like everyone agrees its a HV cap with one end attached to the loop on one side of the tuning cap inside the box. The other end is just left hanging in the air.

    Sure there is some stray capacitance to ground, to the loop and to the tuning cap in series with this 500pf cap. Maybe this stray is 50 pF ( just a guess). These two caps, the stray capacitance and 500pf in series give a total capacitance of 45 pF. I think the experiment would benefit from a field strength (FS) measurement made with 5 Watts and a FS measurement at the maximum power that the compensator is rated for.

    If there is a way to measure loop current that would be nice to have as a check. Both measurements would be made when tuned to match the signal source.
     

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