[Nick3092]

Most radios into the early 40's were designed as long wire radios, meaning no loop. Typically if a radio schematic shows just an antenna terminal on the schematic or shows an upside down triangle, that usually means it's a long wire. Most transformer sets are long wire, but some larger consoles were designed to have a built in loop (like the 40-180).

Most sets designed to use a loop will have a spiral square on the schematic indicating the loop antenna. It's also important to know that the loop was tuned for that particular radio. Meaning a loop from one radio may perform badly on another. Most often these are AC/DC transformerless sets. But not always.