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 AMantenna.
Start with the electrical specifications as described in the companionarticle. Once the loop is built, it must be supported in a ring toyield the best results. One way of doing this is to create a loop ofPVC pipe. This will result in a square if 90-degree elbows are used oran octagon if 135-degree elbows are used. Cutting the pipe andassembling the loop can be time consuming. Instead of PVC, Gregsubstituted a material that is sturdy, almost perfectly round, and inmost cases, easily found in any toy store or discount department store.Greg�s idea was to use a hula hoop, which are available in largeand small sizes. The small size is just right. Some hoops have a seamthat can be easily opened, but if not, cut a hole so the "magic hulabeans" (as Greg calls them) can be removed. The wire is fed through thehollow hoop.
A common hula hoop is a readily available itemthat can be used to house a home-made shielded-loop AM antenna.
For the connector, Greg opened a 75-ohm cable splitter and drilledout the dual-port side. The wire connections were made inside thesplitter shell. The shell was reassembled and then attached to the hoopwith a silicone sealant.
A standard splitter makes a convenient connectorand wire-termination housing.
Greg reports that only drawback to using a hula hoop is that theycome florescent colors that are typically not associated withindustrial-use applications. Greg was able to find a shade of blue thatwas not too objectionable.
The result is a shielded-loop AM antenna in a perfect circle with abuilt-in F connector. His cost of parts was less than $3.00 for thehula hoop. He already had the wire and splitter.