A hundred years ago, the January 1926 issue of theBritish publication Popular Wireless showed how to put together this “ultra” crystal set.  It was designed to  pull in the main BBC broadcast, as well as the then-new transmissions of station  5XX on 187.5 kHz.  That station broadcast from Daventry with high power (then 25 kW), with the idea of blanketing Britain with its signal.

The set was named “ultra” due to the fact that the honeycomb coils were designed such that the primary and secondary would always have their main portions directly next to one another, for maximum signal transfer.