Variable Capacitor Control for a Magnetic Loop Antenna (MLA).

I am in the process of building a magnetic loop antenna but I first wanted to get the variable capacitor working correctly. This is what I came up with. I have yet to test it out and it may need further modifications. In the radio shack there will be a controller board with a speed controller and a rocker switch which both turns the motor on and off as well as controlling the direction of rotation. The motor shaft is electrically insulated from the variable capacitor. The 12V motor has a turning rate of 5 rpm. I put a 6:1 reduction coupler inline which reduces the turning rate to a maximum of approximately one turn per minute. The variable capacitor has a maxim capacitance of 120pF and I plan to use two additional 70pF capacitors which I can switch in parallel with the variable capacitor to increase the range to 190pF AND 260pF. I have some reservations however of this as I fear that there may be arcing over the contacts of the relays which are rated at 40A. These are car relays operating on 12 Volts but the contacts may be too close to cope with the very high voltages encountered with MLAs. As a result, the magnetic loop may not be able to operate at high power. However, this will be a fun experiment. de EI5EM

[@k7iq]

I have a variable cap like that (nothing connected to the shaft) at work I use for technician and engineer interviews. They have to tell me what the heck it is. Sometimes they do not know and guess something like a stepper motor or a switch or a rheostat ! If they don't try to figure it out, they don't get the job :)

[@JamesP6084]

Enjoy the MLA build, I built one similar to yours was getting a lot of noise from the controller board when tuning. Then i built ON5IA Automatic tuner. MLA's challeging and fun to build enjoy your loop. de VK6NJP

[@moonjockclark9491]

Schematic

[@allancopland1768]

Just visiting Tony's page, but posting 'Schematic' is probably the reason you didn't get one. Just a gentle suggestion.

[@2e0txe]

A man of many words. A sentence and especially manors go along way. lol