In 2009, Mark Bauman (KB7GF) developed a working model of the Shared Apex Loop Array to improve his listening experience in a suburban neighborhood in southeast Washington State. From testing, he found that the array provided exceptional bandwidth in a compact size and provided good front-to-back and front-to-side ratio especially for local interfering signals.
The design of the array countered conventional wisdom by spacing a pair of loops only inches apart when state-of-the-art designs called for spacing on the order of ¼ wavelength (over 100 feet on 160meters). Numeric modeling of the array showed that, for closely spaced loops, the spacing between the loops was much less important than the location of the feed point along the base of each loop. This provided the opportunity to simplify the installation because all of the loops could be held in place by a single non-conductive mast that acted as both a spacer and support.
In addition, inserting ferrite beads along the base of the loop to form transformers provided a convenient method of signal coupling as well as a great way to test various coupler locations. Modeling also showed a correlation between the coupler location and the response pattern and backward elevation null angle which was also verified during testing.
Utilizing the inherent front-to-side rejection of magnetic loops made it possible to achieve both front-to-back and front-to-side rejection using signals from only two loops and a single delay line. This simplified the signal combining task, and made it possible to locate all of the signal processing electronics at a single position at the base of the array.
Next, testing commenced on two orthogonal pairs of loops and switching circuits were developed to provide electronic rotation of the pattern. This testing showed that eight individual directions could be obtained using the four loops. These switching circuits included a multiplexing scheme where the switching commands and power were sent on the same feedline that returns the signals from the array. This technique greatly simplifies the installation.
Here is a picture of an early installation of KB7GF's original 10 foot quad loop array utilizing coax loop feeds.
Below is a diagram of the original array using coax loop feeds.
Here are pictures of the original quad loop switch and amplifier.
Below, see an early coupler with coax used as the loop feedline
Below is a picture of the original controller.
Challenges remained, however before a commercial array could be made available. The coax feeds to the loop were cumbersome and complicated the installation so balanced lines and baluns were substituted and provided superior results. Designing the amplifier chain was especially difficult because of competing constraints. These included the need for closely matched input impedance over a wide frequency range (to ensure accurate timing), very low noise (because of negative forward gain), good gain (to overcome signal cancelation), and acceptable linearity.
Below, see a photo of a later coupler with zip cord used as the loop feedlines
Below is a picture of an improved controller that was used to test the unit at various locations. Only three of these were built.
Later, we integrated the switching, combining and amplifying steps into a single unit. Only three of these were built.
These evaluation units were used by WX0B in Texas along with two others. After months of testing under various operating conditions, Array Solutions became an exclusive licensee for the technology and patent.