It was a detection system, but it operated on frequencies that already in use by shortwave broadcast stations (much more prevalent then than now), amateur radio

It was a detection system, but it operated on frequencies that already in use by shortwave broadcast stations (much more prevalent then than now), amateur radio operators, etc and interfered with them. You can get more details on how it and similar systems work at https://en.m.wikipedia.org/wiki/Over-the-horizon_radar https://en.m.wikipedia.org/wiki/Over-the-horizon_radar