Comments by "Sar Jim" (@sarjim4381) on "The Superheterodyne Radio: No really, that's its name" video.

  1. The local oscillator became a big deal for the US Navy during WWII. Some engineers were convinced that radion for the LO could be picked up by enemy ships and sub and used to home in on their position. The superhet made this worse since there was more radiation from the LO compared to older tuned RF and regenerative receivers. Companies like Hallicrafters and Scott played off those fears and designed "low radiation" radios that were supposedly safe from detection. Such "radiation safe" receivers used things like an extra RF amplifier with an additional coil catacomb and tuning condensers to reduce LO radiation below the 400pW (picowatts) limit required by the Navy. The Navy prohibited anyone bringing onboard a radio not marked as being low radiation, and the typical superhet available to sailors was always a high radiation radio. Ships installed radios like the Scott RBO model in radio shacks and then fed programming out to different areas of the ship through the ship's distribution system. They were commonly known as entertainment or "morale" receivers since they could be used to pick up news and entertainment stations from US broadcast band and shortwave transmitters. They were only supposed to be used to listen to US or British stations. Nevertheless, they were commonly used to pick up Tokyo Rose and Axis Sally since both services had the most up to date music on them. The sailors didn't care about the propaganda being broadcast, just the music Although LO radiation was real, how far it could be detected is another matter. Radio companies and some Navy radio engineers convinced the Navy that German shore stations could pick up LO radiation from as far was 1000 miles away! Tests done after the war showed that even under ideal conditions, radiation detection wasn;t possible for more than half a mile away, and it was usually no more than a 100 feet. The Navy spent a lot of money to buy the radiation safe receivers that, as it turned out, really weren't needed, The upside was the radios were also shielded from stray incoming signals and could operate well in a radio
    1