Re: Building a Spitfire transmitter kit
I'd reckon the background hum is modulation hum, being transmitted.
If the earthing is iffy, the Sputfure would work OK but the RF output would have to fight its way oot however it could. If this was via the power supply leads, there's the rectifier diodes in the way, which get turned on and off at mains frequency. So the radiated RF would vary at this rate.
Having an effective aerial and earth allows the RF to bypass this, so the hum disappears.
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