Homemade Magnetic Loop

Image icon Homemade Magnetic Loop.jpg155.38 KB

This is the copper tubing magnetic loop that I'm testing outside. Since it has a stand, it's easier to set or move around and move stable in wind over the MFJ-933 tuner/wire loop. The 12.5mm (1/2") diameter copper tubing is wrapped in high-voltage rubber tape (60 kV) just in case someone were to touch the loop when it was transmitting! The copper look is 3.03m (10') and in inner, inductively coupled drive loop is 0.606m (2').

Tuning for 30m to 10m is via RG-213 coax stubs (outer jacket and braid removed). I used a Marette connector (wire nut to non-Canadian) threaded into one end of the copper tubing so the stubs can be changed. They just slide into the other end of the tubing and I use an MFJ antenna analyzer to adjust the resonant frequency by adjusting how far the stub slides into the tubing. Since small loops are very shape in tuning, it's often just by millimetres!

The basic design for the loop came from Stephen, WA8LMF, http://wa8lmf.net/ham/30m-magloop-ant.htm, and I made slight changes so it would work multi-band with stubs you can swap in and out. The loop works very well from my WSPR tests. Even at 500mW and 50 percent loop efficiency (20m and 90 percent for 10m), I'm hearing European stations and they are hearing me. At the 200mW level I'm only heard on this side of the Pond. Still remarkable because compared to my outdoor wire antenna 50m Delta loop, the small magnetic loop is producing the same WSPR tx/rx pattern! So, small loops can and do work, if properly designed.

As it's sitting so low to the ground, the loop's orientation doesn't matter as it seems to be omni directional. In the picture, east/west is broadside to the loop. The yellow, collapsible work stand came from an outdoor halogen light stand. The legs can go flat against the ground and a sandbag or some other weight can be used to hold it down in the wind.

Robert, VA3ROM