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Unusual Variable Inductor

jw0752

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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  • 0

    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.

  • 0 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

  • 0 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.

  • 0 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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