Ham Radio

DIY Magnetic Loop – Part 2 – First Prototype


This post is part of the series DIY Magnetic Loop

Other posts in this series:

  1. DIY Magnetic Loop – Part 1 – The Capacitor
  2. DIY Magnetic Loop – Part 2 – First Prototype (Current)

DIY Magnetic Loop – Part 2 – First Prototype

You can find the first part here.

Capacitor of Choice

One day I was talking to my friend Sammy KD2KMP about the antenna design and he was kind enough to send me one capacitor from an American company called Oren Elliott.
They produce high quality products and you can even get a custom capacitor design.

DIY Magnetic Loop capacitor

This capacitor is rated for 5Kv RMS and capacitance range of 10pF to 154pF.
The total length is 272mm long and it has 2 sections.

The calculations show that I need between 17pF and 151pF for tuning to 30m-10m bands and I had to give up on 40m.
I’ll need a bigger loop (around 4 meter) to get 40m with my capacitor.

Those are the results I got from the calculator:

Length of Conductor (antenna “circumference”) 3 M Secondery Loop circumference: 0.6 M
Diameter of Conductor 2.6 CM
Frequency 10-30 MHz
Transmitter Power 100 Watts
10 MHz 30 MHz
Antenna efficiency 37% Antenna efficiency 97%
Antenna bandwidth 6.91 KHz Antenna bandwidth 216 KHz
Tuning Capacitance 114 pF Tuning Capacitance 13 pF
Capacitor voltage 4,501 VRMS Capacitor voltage 2,412 VRMS
Cap range 13-114 pF
Voltage 6,364 Volts

On 20m band I get around 66% efficiency.

I chose a plumbing pipe with diameter of 2.6cm for the final antenna.
More details will be provided on the next part.

First Prototype

I didn’t have the plumbing pipe yet and couldn’t wait so I took an electric wire from my cables pile and connected it to the capacitor.
The wire has 3 internal copper wires and it’s mainly used for in-wall electric wiring, each wire is 2mm in diameter.
I knew it wouldn’t be effective for transmitting due to the fact that RF presents on the outer shell of the conductor (skin effect) and 3 wires close to each other will have weird radiation pattern.
But I wanted to try and receive some signals.
The wire was attached to piece of scrap wood with zip tie and the capacitor was fixed to the wood with some screws.

DIY Magnetic Loop Prototype

The wire was around 3 meters long and at the moment I tuned the capacitor I was shocked.
It actually worked and I could hear 20m band inside my room.

I decided to go and do some shopping!
73 for now!

P.S I hope that the next part will be published faster than the this one.
Sorry for the delay.

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