The 4G LTE modules we use are brand new and have only been available for a few weeks. I just stocked the LTE bee adapter board in our Amazon storefront last week too, so the materials you need for building the signal tester are so new that I haven’t had a chance to document the building and programming process. I’ll be building a few more once I get back in the office in early August after all my workshop and conference travels currently happening, so hopefully I can post some instructions and code so you can build your own. In the meantime, you can use any AT&T cell phone to see if you’ve got LTE coverage. When we were using the older 2G GPRSbee modules, they utilize T-mobile networks that are starting to be phased out all over the country, so having a dedicated 2G T-mobile signal tester was the only way to test for the specific coverage that those modules needed. It also helps that my new LTEbee adapter has a signal strength indicator LED on it so just powering the board with a module attached will give you an instant indicator of signal availability and strength, even without programming the Mayfly and having a dedicated LCD display.