When enthusiasts built their own transmitters, receivers and antenna systems a neon gas filled tube was used to “tune” vintage radio transmitters and receivers.
By holding the neon gas filled tube (top square in simulator) near (not touching) a devices radio frequency field and observing the light intensity and making adjustments to improve signal output. The brighter the light, the better the signal output.
A neon gas was injected into the glass tube and heavy molded Bakelite caps covered the ends.
