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  • variable_inductor
Related

Unusual Variable Inductor

jw0752
jw0752 over 10 years ago

I was digging through my electronics graveyard and I found this interesting variable inductor. It has a ceramic drum wound with 14 gauge silver alloy wire. I measure a minimum to max range of 1uH to 12uH. As the drum is turned a small idler wheel rolls over the coil as a variable tap changing the amount of the coil that is included in the circuit. I was hoping that someone could tell me more about its original application. The square plates on the frame are 6.2 cm on a side and the length of the body is 9.5 cm. The front main shaft is coupled to the drum with an insulated universal joint. I see a shadow on the ceramic where there was likely a label at one time but it is gone now. If I can get a little more information about it I will put a tag on it so the next time someone runs across it there will not be a mystery.

 

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Thanks John

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  • D_Hersey
    D_Hersey over 10 years ago +2 verified
    To me, it looks like a medium-power 'roller inductor.' The gear makes me think it was intended to be operated by a motor. The most likely application was to tune an HF antenna. Yup, HF autotuner is my…
  • D_Hersey
    D_Hersey over 10 years ago +2
    I think due to its scale that this was used on the transmit side to normalize the load. The application circuit would have been along these lines: Pi-Match | Electronics and Electrical Engineering Tools…
  • jw0752
    jw0752 over 10 years ago in reply to shabaz +1
    Hi Shabaz, I was thinking that the operator had to watch a meter and power the motors manually but if I understand you correctly the motors would auto tune the antenna using an algorithm. this is pretty…
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  • D_Hersey
    0 D_Hersey over 10 years ago

    To me, it looks like a medium-power 'roller inductor.'  The gear makes me think it was intended to be operated by a motor.  The most likely application was to tune an HF antenna.  Yup, HF autotuner is my guess.  Probably tunes a resonant trap to keep the RF load around 50 ohms as the amp sees it.  I think the ARRL 'Antenna Handbook' or some such may be for you.

     

    You should consider getting a HAM liscence.  Or 'license' depending upon which side of the pond you are lurking at.

     

    Are you aware of 'fractal antennas?'  Neat stuff.

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  • jw0752
    0 jw0752 over 10 years ago in reply to D_Hersey

    Hi Don, I searched "Roller Inductor" on the web and found that you are correct about what it is. I will add this information to my tag on the Roller Inductor. You even explained what the gear on the main shaft was for as I can see that it is not uncommon for these to be motor driven. As far as becoming a HAM radio operator, well we will see. Thanks for the great reply.

    John

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  • shabaz
    0 shabaz over 10 years ago in reply to jw0752

    Hi John,

     

    I also agree with Don's assessment. You can see the insides of an ATU at this URL, in action: https://www.youtube.com/watch?v=AnztAIWnSxo

    (it shows motorized variable capacitors instead of variable inductor, but the principle is similar).

    I think this was an early way to do it, but a later method was to use relays to switch in inductors and capacitors, i.e. no need for motors.

    It was fun to watch them in action, there would be a buzzing sound as all the relays clicked in an algorithm (i.e. briefly transmitting while measuring the amount of

    transmitted or reflected signal) until the antenna was best tuned.

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  • jw0752
    0 jw0752 over 10 years ago in reply to shabaz

    Hi Shabaz,

    I was thinking that the operator had to watch a meter and power the motors manually but if I understand you correctly the motors would auto tune the antenna using an algorithm. this is pretty cool and not what I expected from older technology.

    John

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  • jw0752
    0 jw0752 over 10 years ago in reply to shabaz

    Hi Shabaz,

    I was thinking that the operator had to watch a meter and power the motors manually but if I understand you correctly the motors would auto tune the antenna using an algorithm. this is pretty cool and not what I expected from older technology.

    John

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  • shabaz
    0 shabaz over 10 years ago in reply to jw0752

    Hi John,

     

    Indeed, very cool technology. There may have been manual versions, but the more advanced ones could do it all automatically.

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