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THE THICK LOOP

The performance of a small magnetic loop can be improved constructing it larger, thicker or both.

My main goal was to improve the performance of the magnetic loop antenna on the 40 meters band.

One of the challenges was to build this loop light enough to be carried on my outdoor radio activities.

We have two options to build a reasonable performer on 40 meters band:
A) Build a 6 ft. diameter magnetic loop on 3/8 inches soft copper tube.
B) Build a 3 ft. diameter small magnetic loop on a 4 inches tube.

I was searching for lightweight tubing that could be easily bent into a circular shape.

 

I selected the 4 in. diameter extendable aluminum chimney tubing.

I used standard 4 in. water pipe as the loop’s basic structure.

 
     
 
     
 

This piece of pipe will at the same time keep the loop stable and house the variable air capacitor inside it.

 

I inserted a piece of 1 in. pipe into the center of 4 in. base.

I inserted the other end of the PVC pipe trough two holes opened on the bottom center of the loop.

An extension shaft coupled to the variable capacitor placed inside the 1 in., 4 ft. pipe allows for tuning the loop at hand holding level.

 

The ends of the aluminum tubing are attached to the PVC pipe by 12 screws on each side.

Details of the connections:

A half inch tined copper braid was used to connect the aluminum tubing ends to the variable capacitor.

On each of the aluminum tubing ends the braid encircles it and the tubing tips are folded back one and a half inch; thereby improving the electrical contacts which is further enhances by the pressure of the twelve screws securing the tubing’s ends.

The other ends of the braids are soldered to the variable capacitor contacts.

   
Non working loop
 
Aluminum foil and polyester film
 
Covered loop

To make the loop work its aluminum tubing was covered with aluminum foil and the foil was kept in place by polyester film.

This procedure of the preliminary tests witch proves that the corrugated aluminum tube was not suitable for resonating on the desired frequency range.

 
     
 
Capacitor box (rear view)
Capacitor box (front view)

The antenna is covering from 12 Megahertz to 32 megahertz and adding a 156 Pico farads ceramic capacitor it resonates on the 40 meters band.

I would like to thanks for his help in translation to GABRIEL BOKOR PY1CJZ, former Collins Radio Field Service Engineer, my old friend and colleague.

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