The main reason for going in for Magnetic Loop Antenna (MLA) is to avoid very high local noise problem around my QTH.

I have no limitation of space for any type of antenna; infact I have been using full size ground loop cut for 40M, giving me multi-band operation on 40,20,15 & 10M. But the local QRM on 40 & 20M bands is S6-S7 and sometimes even more! Receiving stations on these bands is nearly impossible!

Very narrow BW of MLA, acting as a razor sharp filter at front-end has solved the QRM problem. Shall report the results by Feb 2014 end.

I have used a bipolar 4-wire stepper motor (salvaged from an old EPSON printer) for tuning the high voltage air variable capacitor of the mag loop. It is working beautifully.

( I have used a very simple driving scheme for stepper motor involving a band-switch and four resistances. It has an analog-type tuning feel and the scheme can be used for unipolar or bipolar steppers in full or half stepping mode. Details of circuit dia and fabrication steps will be shortly up-loaded on this site)

The main loop dia is about 94Cm. The driving loop dia is about 18Cm. The copper wire bundle dia is approximately 6-7 mm. The HV variable capacitor was picked up from an old tube 100W final power amplifier. It has three sections. One section has been left unused. The other two section are used in butterfly configuration to increase the voltage break down rating; resulting in a nice 75pf HV variable capacitance with no sliding contact.

More capacitance was needed to tune the loop down to 40M band. For this three Silver Mica caps of 470pf (500V) each were connected in series to form a high voltage capacitor of about 150pf. This capacitor was connected across the variable cap through a 12V relay for 40M band operation.

       And finally..installed on the roof top for action!!

Flex Board jig for making the copper wire loop, radius 3'. I used a bundle of bare copper wires as I had them in stock. You can use 1cm dia copper pipe generally used for refrigeration.

 Making of main loop using a number of bare copper wires.

Completed loop with HV variable capacitor attached. Copper loop was covered with Teflon tape for weather proofing.

 Tuning box, made of Flex board, containing 4-wire Bipolar Stepper Motor, reduction gears, HV variable capacitor, 40M switching Relay, 3 HV caps connected in series for 40M band operation and two 5-pin connectors for capacitor rotation commands and antenna band switching.

 1/5th dia excitation loop

Completed antenna for pre-testing. The Mag Loop tested and installed in horizontal position for omni-directional pattern.