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The G0CWT Small Tuned Loop

I will first describe a 40-meter loop that can be placed in almost any location; I have one mounted on the roof of my mobile home. It can be pulled up into position from inside the vehicle in less than 3 seconds.

 
I use this loop on 40, 80, and 160.meters.
 

First, I will describe the 40-meter version,

The element is one-quarter wavelength of wire or coax minus about 5% and is approximately 32 foot long.

To support this loop I use a fiberglass fishing rod for the vertical support and a six-foot spreader, which is made from fishing rod tops.

 

The tuning and matching unit is mounted inside the roof of the van where it is easily accessible. This removes the need for remote control tuning it also allows me to make many tests and experiments.

Below is a picture showing an MFJ259 analyzer that has been modified by wiring a digital meter across the MFJ impedance meter to resolve a more accurate reading.

 

 


On 80 meters, the loop becomes a 1/8 wave and the input impedance is now only 2.249 ohm and the transformer turns ratio is approximately (4.5 to 1) this is 9 turns to 2.


Because of the extremely low input impedance at the 160 mtr or 1/16, wave loop, the input impedance is only (0.2278 ohms) the number of turns on the primary is 20 turns.


Therefore the primary of the transformer consists of 20 turns tapped at three turns and again at nine turns which means that the input to the transformer has four wires.- 1,= start.  2,= three turn tap. 3, = nine turn tap. and no4,= twenty turns.

This transformer will then match the 50 ohms of the transceiver to the input impedance of the loop at 1/4, 1/8, and 1/16 wave.

This means that you can switch through 40, 80, and 160, by using a suitable switch to the primary of the transformer.


As can be seen in the pictures the loop support is a fishing pole with a cross member at the top. The pole is pivoted on a four-legged support. There is an extension at the bottom of the pole that overhangs the pivot, to this is attached a cord that runs through to the inside of the van where it can be used to pull the loop into position when required. The loop element (coax or flexible wire) is attached to the top spreader and the ends bought down to pass through into the roof of the van and there connected to the Tuning and matching unit.

 

 

   Ben@Edginton.info

All rights reserved. B Edginton. 2004

 

Email: ben@edginton.info

Ben Edginton 2012                       Last Updated:May 2012