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Loop Antenna
I had need for a loop antenna and so set about designing one from scratch. Loop
antenna's are highly directional and my finished version works exceptionally well. The
circuit is simple enough but the tricky bit is making a sturdy, wooden frame to hold the
wire which will be the antenna.
- Start by making the arms for the frame...
- When this is done take four 12-way, 2-Amp connector blocks and attach one 12-way block
to the end of each arm. These will be used to hold the wire for the antenna.
- Fix 5mm-thick plyboard to the framework and drill a hole for VC1. Be sure there is
enough clearance to fit the capacitor without it snagging the frame and damaging the
vanes.
- At this point you may want to fix the mast/base sections to the frame. This will make
winding the wires much easier (see the drawing, below).
- Starting from VC1, wind the first winding (L1). Thread the wire thru the outer-most
connector and wind spiral-fashion until you have eight complete turns.
- You may notice the frame becoming distorted as the wire is added. For extra rigidity it
may be wise to add two or more support struts between the arms as shown in the drawing
below.
- Tighten each screw in the connectors as you go making sure the wire is kept taut between
each arm of the frame.
- Terminate the other end of L1 to VC1
- Start L2 from the 2-way connector block on the rear of the mast and thread thru the last
(inner) two series of connectors.
- Wind two complete turns and terminate back at the 2-way connector. At this point you
should connect a short length of 50-Ohm Co-Ax cable terminated in a PL259-type plug.
- This completes the loop antenna and you are now ready to try it out on the bands.
Expanded view:
Using the Loop:
- Tune your receiver to the desired frequency
- Rotate the antenna to the direction of transmission
- Adjust VC1 to peak the received signal
The loop is highly directional. If two countries are transmitting on or near the same
frequency, simply rotate the loop to 'null-out' the offending station. My prototype covers
approx. 2MHz to 6Mhz. Adding or removing windings on L1 and the overall size of the frame
will alter the final frequency coverage. All dimensions are non-critical and you are free
to experiment. My windings are done with 24-guage enamelled wire which was all I had at
the time. If you use this remember to remove the enamel off the ends before soldering.
For more details of wire thicknesses, see Wire Guages on the
Index page.
