Unusual Variable Inductor

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.

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.

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

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.

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

Hi John,

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