Variation on the Shielded-Loop AM Antenna
Mar 25, 2002 12:00 PM
Greg Manfroi of WIUM/WIUW, Western Illinois University, Macomb, IL, sent us this idea on a construction method for the shielded-loop AM antenna.
Start with the electrical specifications as described in the companion article. Once the loop is built, it must be supported in a ring to yield the best results. One way of doing this is to create a loop of PVC pipe. This will result in a square if 90-degree elbows are used or an octagon if 135-degree elbows are used. Cutting the pipe and assembling the loop can be time consuming. Instead of PVC, Greg substituted a material that is sturdy, almost perfectly round, and in most cases, easily found in any toy store or discount department store. Greg�s idea was to use a hula hoop, which are available in large and small sizes. The small size is just right. Some hoops have a seam that can be easily opened, but if not, cut a hole so the "magic hula beans" (as Greg calls them) can be removed. The wire is fed through the hollow hoop.
A common hula hoop is a readily available item that can be used to house a home-made shielded-loop AM antenna.
For the connector, Greg opened a 75-ohm cable splitter and drilled out the dual-port side. The wire connections were made inside the splitter shell. The shell was reassembled and then attached to the hoop with a silicone sealant.
A standard splitter makes a convenient connector and wire-termination housing.
Greg reports that only drawback to using a hula hoop is that they come florescent colors that are typically not associated with industrial-use applications. Greg was able to find a shade of blue that was not too objectionable.
The result is a shielded-loop AM antenna in a perfect circle with a built-in F connector. His cost of parts was less than $3.00 for the hula hoop. He already had the wire and splitter.