Radio interference from Edison bulbs – Good Article Alert

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If there’d been VHF in the 19-teens, there would have been a big radio interference problem – from light bulbs.

We know this because we’re getting RF noise from some of the new vintage-style bulbs that are in production these days. There’s evidence that Rustika brand ones, for example, are accidental Barkhausen-Kurz oscillators.

So says Dr David Lauder, in an absolutely fascinating article in this month’s RadCom,1 the publication of the Radio Society of Great Britain.

Modern bulbs – the ordinary kind – don’t do this. But the Edison ones, the only ones in use before 1913, did. Their tungsten filaments emitted electrons thermionically, as from a cathode; some of the supporting wires inside the bulb could function as anodes. Presto! You had a houseful of vacuum tube diodes! ‘If the bulb was powered by DC mains,’ explains Dr Lauder, ‘the oscillation would be a coherent carrier’.

Sure enough, this is what some of the modern retro bulbs do, and they generate what amounts to wideband FM with sidebands smack in the middle of aviation radio, right next to the 2-meter amateur band.

Apparently, Edison bulb interference did become a problem eventually, that endured into the 1950s, when the last of the bulbs burned out. Typically, it was television interference between 41 and 68 mHz.

 

 

 

1 August 2020, Volume 96, Number 8, pp. 74-5.

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