Sixty years ago this month, the March 1966 issue of Electronics Illustrated showed how to build this 3-tube TRF regenerative receiver for 10-30 kHz VLF, as well as the loop antenna. The magazine pointed out that two categories of stations could be heard. The first was time-frequency standard stations such as WWVL. It noted that reception was more stable, since the ionosphere was not involved. The second category was CW stations such as NAA, on 17.8 kHz from Cutler, Maine, transmitting to submarines in most of the world from the world’s most powerful transmitter. Some of the other possible catches are shown on the chart below.

Calibration could be accomplished with an audio signal generator. Since the signal generator probably wouldn’t go all the way up to 30 kHz, the magazine recommended using the second harmonic of a lower frequency to calibrate the top of the dial.