[RodB]

Most loop antenna setups are either one continuous loop with two connections or 2 loops with 4 connections. The latter can be considered an rf transformer with the primary winding capabile of attachment to an external antenna, the secondary to the rf amp tube. So, you should get continuity on one pair and continuity on the other. In addition the antenna is usually used for a path of the AVC connection to the grid of the rf amplifier. The link that Ron provided above has this clear example of your antenna.

SAMs and Riders came after the fact and I believe they worked with most manufacturers to get their info. At times there's no way they would be able to know all the makers of radios. Beitman Supreme Publications are another source though they don't have complete coverage of all models, as they publish *the most popular schematics". Their diagrams are usually very clear but limited to just the schematic and sometimes alignment data.