Wednesday, July 3, 2019

Calculate tuned circuit values in your head

There was a good response to my video post on radio circuit modules a few days ago.  So here's another. In this video I discuss calculating tuned circuit values in your head. That could be handy for various transmitter, receiver and antenna projects. 

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1 comment:

  1. From Dale - W6BYU

    I enjoy your “daily antenna” blog, and marvel at how long you have managed to keep it going. I had enough trouble doing one article a month for a newsletter, but those were longer.

    However, I’ve tried to post comments a couple times and don’t know that they have showed up, since I don’t have a Google login.

    But I wanted to note a simple formula that I use for calculating coils and capacitors in my head that also gives reactance.

    For a coil, the inductance for a 200 ohm reactance is given by the wavelength (in metres) divided by 10.
    For a capacitor, the capacitance for a 200 ohm reactance is given by the wavelength (in metres) times 3.

    So for 80m, it would be 8 uH and 240 pF.

    I can then scale from there as needed.

    No, it isn’t exact, but close enough to give a good starting point, especially with hand-wound coils that won’t be precise anyway. It’s actually quite easy to work out problems while driving the car or mowing the lawn, and a 200 ohm reactance is a reasonable value for many tuned circuits.

    Keep up the good work!


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