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5450Re: [loopantennas] Remote tuning

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  • Jim Dunstan
    Aug 1, 2008
      At 11:18 PM 7/31/2008 +0000, you wrote:

      >So, it occurred to me that it would be good to come up with a cheap
      >and easy way to turn a tuning capacitor on a loop that is mounted
      >somewhere outside.
      >Now this is just an idea... I have flow radio control (aka R/C) model
      >aircraft for many years.
      >The receiver and servos that operate the control surfaces in the
      >plane run off 4.8 v nicad packs. Actually, they will run on anything
      >from 4.8 v - 6.0 v. So, if power can be sent out to the antenna this
      >could be made to work.
      >Tuning capacitors rotate 180*. Most servos only rotate 90*, but can
      >be modified to rotate further.
      >Inside the servo is a feedback potentiometer driven by the output
      >gear of the servo. These pots are usually 10k ohms. By attaching a
      >4.7 k 1/8 w resistor on each outer terminal of the pot, and
      >connecting those leads to the resistors, the servo will now rotate
      >Now a direct connection can be made from the servo's output shaft to
      >the tuner shaft with a piece of rubber or vinyl tubing.
      >A cheap two channel R/C car/boat radio system can be used for this,
      >under $100.
      >Just a thought...
      >Paul C.

      Hi Paul,

      Yes it can be done. Whether you use a wire connection or a wireless
      connection (R/C) ... the problems are mechanical in nature. I have seen
      some locals using remote control of the variable capacitor and the problem
      they had was slowing the servo motor sufficiently for smooth tuning. Often
      disabling switches are used at either end of the variable rotation. It is
      really the only way to go if you are using the loop to carry any
      significant power. A receive only loop is best tuned remotely with
      varactor diodes.

      Jim, VE3CI
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