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The motor tuned loop

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Control cable and coax ..............................Plastic case and Knob...

This antenna is made on 3 meters and 26 centimeters of 9 MM. soft cooper tube with 50 Pico farads butterfly capacitor. The excited loop have 1/5 of the main loop as a common law on the loop construction and it is made with coaxial cable with the braid soldered to the inner wire.

To home brew a motor tuned loop, you will need a 12 volts DC motor coupled to reduction speed gear box.

You will need a non conductive material to couple the aisle of the capacitor to the aisle of the reduction box.

The motor aisle pass trough a hole on the protection plastic box and a knob screwed to the aisle indicates the motor rotation.

Magnetic loop motor control box

The DC voltage must come from a PWM (pulse width modulation) circuit to power the motor with a train of pulses.

This circuits can be searched by "GOOGLE" under the name of "DC Motor Speed Control" or "Motor Speed Control".

This simple circuit uses one or two 555 integrated circuits and one transistor.

On my control unit I have made some additions on the original schematics.

The most important one is a relay system controlled by the command of two small pressing buttons for a sensitive forward and reverse motor direction.

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The antenna works continuously from 14 MHz to 30 MHz and with the plug in capacitors I can work on 30, 40, 60 and 80 meters.

I can operate this antenna on my backpack having the control box clipped on my belt by a cell phone clip or attached to the FT 817 by rubber bands.

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I can use this antenna on rainy days from my shack. The boom wood was water proof treated and I protect the black plastic case with plastic bags.

For QRP base operation from my shack I develop a window aluminum knee, that keeps the antenna upright facing the window (when not in use) or horizontal positioned for operation position.

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...........HF QRP SHACK ..............................CONTROL BOX-FT817-DR36...

 

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...ARTICULATED WINDOW SUPORT................ LOOP ANTENNA ATACHED.........

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.......UP RIGHT .................LOOP ON STAND BY POSITION ..

 

PY1 AHD ALEX (Alexandre Grimberg).

e-mail: py1ahd@ig.com.br