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THE LIGHT LOOP

Small magnetic loop ready for a hand held walk and talk operation
 

My main goal was design a lightweight magnetic loop antenna to be hand held on QRP pedestrian operation.

This small magnetic loop can be temporarily fixed on a balcony with a plastic clamp, or installed on a car by the magnetic “Coke-Mount” designed to operate static mobile. On both situations the tuning knob is easily hand reached for antenna adjustments.

One of the challenges was to build this hand held loop with the variable capacitor on the bottom and the inner loop on the top to optimize the antenna’s gravity point to improve the weight balance.

The antenna weight is less then 690 grams.

The normally used extension shaft coupled to the variable capacitor was changed by a small plastic knob for tuning the loop at hand holding level.

The antenna loop is made on 271 centimeters of RG213 coaxial cable and the inner loop is made on 54 centimeters of electric copper wire.

The variable capacitor is a multi gang AM/FM/SW portable radio unit.It has small plate spacing; but despite of this I have no arching problems working on QRP power levels.

The variable capacitor as 5 moving and fixed gang plates and I connected each extreme of the loop on a group of fixed plates to avoid electrical contact losses. The variable capacitor fixed gangs was combined in series resulting in 80 Pico farads.

Balcony operation
Step by step mounting details
 
 
 
Cable and connector ready for a plug and play operation
 
Inner loop mounting details
 
The antenna covers from 12 Megahertz to 34 megahertz, and a add on 150 Pico Farads ceramic capacitor is plugged to operate on the 40 meters band.
 
 
 
Small magnetic loop weight
Final tests

The exclusive magnetic “Coke-Mount” base was designed to operate static mobile

Magnetic “Coke-Mount“
 

Magnetic “Coke-Mount” parts list:

A) Loudspeaker magnet
B) ¼ Coke plastic bottle
C) ½ Cream cheese plastic cup
D) Thermal fax paper inner tube

PY1 AHD ALEX (Alexandre Grimberg).
e-mail: py1ahd@ig.com.br