Seventy-five years ago, the BBC realized that it needed to start broadcasting on VHF. The reason was simple: The mediumwave band in Europe was too crowded. But unlike America, which had been using FM on the old 42-49 MHz band, and was about to move to 88-108, Britain hadn’t decided on whether to use AM or FM modulation on the VHF band. In order to decide, they ran a test in the London area. From the same antenna, two signals would be broadcast, both carrying the same program. The transmitters are shown above, from the October 1951 issue of Radio Electronics.

Both transmitters used approximately equal power, with the AM signal going out over 93.8 MHz, with FM on 91.4.