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After we consider a spark hole radio transmitter, most of us instantly think about an early twentieth century ship’s radio room or related. Most of us know these transmitters as the primary radio methods, and from there we’ll most likely additionally know that they had been phased out when higher circuits arrived, due to their extensive bandwidth. So it’s uncommon in 2024 to seek out anybody characterizing a spark hole transmitter, as [Baltic Lab] has.
The circuit is easy sufficient, a excessive voltage passes by way of an RC community to a spark hole, the opposite facet of which is a tuned circuit. The RC community and the spark hole type a easy low frequency rest oscillator, with the C being charged till the spark hole triggers, forcing the following discharge of the capacitor and inflicting the spark to extinguish and the cycle to repeat. The ensuing chain of excessive voltage pulses repeatedly energizes the tuned circuit, with every pulse inflicting a damped oscillation at its resonant frequency. The ensuing RF sign is a crude AM tone which could be acquired pretty merely.
The arithmetic behind all of it is fairly attention-grabbing, revealing each the reason for the bandwidth unfold within the low Q issue of the tuned circuit, and the presence of a big spurious frequency spike on an interplay with the capacitor within the RC circuit. It’s all within the video under the break, and we have now to confess, it taught us one thing about radio we didn’t know.
In the meantime spark gaps weren’t the one early radio transmitter expertise. How about an alternator?
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