Building a VLF antenna

For our purpose, the antenna does not need to be tuned and many designs are possible. This design is small, simple and relatively easy to "hide".
The antenna consists of 40 to 50 turns of copper wire wounded around a 60cm (24″) square frame. The dimensions and the wire wounds do not have strict tolerances.

The following items are necesary to build the antenna:

• One frame 70x100cm (27-½ x 39-¼″) Ikea RIBBA or similar. It has to be at least 35mm (1-3⁄8″) deep.
• pine corner molding 22x22mm (7⁄8"x7⁄8″)
• TNC-Female Bulkhead 50Ω Connector
• Magnet wire (solid copper wire with varnish insulation) #26 (diameter 0.4mm - cross sectional area 0.13mm²). About 150m (500ft) long.
• wood glue
• For the cable: RG-58 Coax cable (length as needed) and two male 50Ω TNC connectors.

The author has built two of those antennas and has measured the following characteristics:

	Theory	Antenna 1	Antenna 2
Inductance	5.77mH	5.92mH	5.63mH
Resistance	15.6Ω	17.3Ω	17.0Ω
Capacitance	129pF	Not measured	Not measured

The theoretical values have been calculated from the equation described in the page dedicated to the loop antenna theory.

Here is the original frame front and back. You can click on the images to enlarge them.

First, draw a 60cm (24″) square centered on the frame. Draw its diagonals.
Then, cut the corner moldings so that they fit the square diagonals (see pictures).
Cut a 1cm (½″) long dent at each end of the corners, about 3mm (1⁄8″) deep.
Cut a corner of about 8cm (3″) and drill in the middle a 10mm (3⁄8″) hole to hold the TNC socket.
Glue strongly the diagonals and the corner holding the connector a few centimeters/inches away from the square.

Finally, wind 40 to 50 turns of wire around the diagonals, use adhesive tape to secure the wire ends.
Cut a small corner of about 4cm (1-½″) and make one 5mm (¾″) deep notch at each end with a cutter. It will be used to lock the wire ends before they are linked to the socket.
Glue the small corner just behing the connector. It has to touch the antenna winding.
Each wire end is then locked in the notches before being soldered/crimped to the connector.

Now, you just need to found a nice poster and fix the frame to the wall... Only the cable may betray the presence of the antenna!

References

You will found precious information in the following books:

• The ARRL Antenna Book
• The ARRL Handbook for Radio Communications