Discussion in 'General Technical Questions and Answers' started by KB2WVO, Apr 16, 2018.

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  1. KB2WVO

    KB2WVO Ham Member QRZ Page

    ok tryin to learn loading coils. tuners and antennas.

    iam wondering if i understand this a little if at all.

    the inductor say is built to 10 henrys. size and such no importion right now..
    at 10h it resonates at say 3.9mhz
    but to resonate at say 7.2mhz you change the tap in turn chaging the value of henrys. to make it resonate at 7.2
    the variable caps in a tuner is for fine tuning the coil to get to resonates.

    you would build a coil to your lowest op freq say 3.9 and it should in turn work from 3.9 to say 18.15mhz

    so up in henrys is lower in freq. down in henrys is higher in freq.
    or am i way off base.. remember please.. iam a ID 10 Error here lol ..
    Last edited: Apr 16, 2018
  2. KE0ZU

    KE0ZU Ham Member QRZ Page

    You've got the right idea.

    As you know the actual inductance needed is much smaller.

    Have fun.
    KB2WVO likes this.
  3. W5DXP

    W5DXP Ham Member QRZ Page

  4. KL7AJ

    KL7AJ Ham Member QRZ Page

    Here's something interesting I demonstrate in my electronics classes. The INDUCTANCE of a single layer solenoid is proportional to the SQUARE of the number of turns, all other things being equal. Which means that if you double the number of turns you have four times the inductance. But, interestingly enough the formula for resonant frequency is 1/2pi times the SQUARE ROOT of LC. This means that the frequency changes only as the SQUARE ROOT of the inductance. But, lo and behold, as we already know the inductance is the number of turns SQUARED. it turns out, the resonant frequency is the simple inverse of the number of turns (or rather proportional thereto). So, double the turns to get half the frequency. Pretty cool.

    AI6KX and KB2WVO like this.
  5. W5DXP

    W5DXP Ham Member QRZ Page

    Eric, cool but lest anyone parse that statement incorrectly, here's the equation:

    WB5YUZ, WA7PRC, KC8VWM and 1 other person like this.
  6. KB2WVO

    KB2WVO Ham Member QRZ Page

  7. WB2UAQ

    WB2UAQ Ham Member QRZ Page

    Maybe this will help: ~0.159 is 1 divided by 2 Pi. I didn't read the article:)

    Inductors are interesting when you state a given inductance. You always need to specify the frequency where you want a given inductance to be used. This is because there is capacitance between the turns. Maybe this was covered in some of the links given here.
    Not the case for your air-cored inductor but if the core is ferrite you also have to state the level of the signal applied by the test instrument because the permeability of the core is level dependent.
    KB2WVO likes this.
  8. KL7AJ

    KL7AJ Ham Member QRZ Page

    Thank you! I didn't know how to get those fonts on here. :)
  9. KL7AJ

    KL7AJ Ham Member QRZ Page

    Indeed....the implied assumption is ideal inductors. Things get a lot more complicated with multiple layers, and permeable cores. :) But you gotta start somewhere. HI!
  10. KL7AJ

    KL7AJ Ham Member QRZ Page

    Might also state that it's impossible to state the Q of a coil without the frequency, since Q is dependent on reactance, not inductance!

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