Please read the description first to get the best information. IMPORTANT: 1 flaw in the schematic: the 10 N capacitor in series with the 4N7 capacitor must be connected to minus (-), thus to the middle (!) of the coil.
NB: next circuit (a kit from Ali, tested 28 jan 2025) is here https://youtu.be/g3mMh8lbvDQ?si=EIvV1xctMfZvMSHB That Ali kit does not work better, by the way. But it has certain good properties.
Important: in the circuit (now & here 26 jan. 2025) you see "CX". In practice it is realized by the combi of the 4N7/1N (bridged) and the 10 N/4N7 (in series). The indication is (thus) more or less "theoretical" (forget it in practice).
Circuit of an AM transmitter with a tiny (antenna) output. It works in the Milliwatt range. The circuit takes 0.8 mA at 3 Volt (2 carbon zinc or 2 alkaline batteries in series). That is 3 Milliwatt input, thus perhaps 1 MilliWatt sent out (in e.m. terms) via the transmitter coil in the AM frequency range. The oscillator works on 3 Volts.
So a safe circuit, even without filters to filter out the harmonics of frequencies to which it is tuned in the AM radio band (800 KC-1.8 MC). The sent-out harmonics are always weaker, compared to the ground frequency, here in that AM band. Transmission reach for proper receiving the transmitted AM radio signal is approx. 40 centimeters.
The idea is this:
When you like the sound of a classic tube AM radio (or old transistor radio from the 1970s or so, working between say 800 KC-1.6 MC) you can put this mini transmitter next (very close) to that radio (10 cm. - 40 cm; or on top of it), so that it strays out (in the MW radio band) the music or whatever files coming out of our MP3 player or smartphone.
Perhaps even MP3 (or other sound) files) via a bluetooth dongle.
Important: I must test that (the bluetooth dongle idea) in the future. So now (this video, uploaded 26 january 2025) is only about playing music via a standard audio wire, connected to the output of a MP3 player or a smartphone or so.
About the AM coil that has to work somewhere in the AM radio band, going from say 550 KC to say 1.6 MC.
The video shows how the coil was made, also the schematic shows good ways to make it.
Say: 2 x 40 windings of laquered copper wire with a diameter of 0,4 mm, on a paper roll of 1 cm. in width, in which you can stick into a ferrite rod of (say) 8 cm length and 0,8 cm in diameter. The ferrite rod must be free to move in-out inside that paper/cardboard tube.
When you move that ferrite rod in-out you can tune in the AM band. The reason why this coil is quite “big” is that it serves as a transmitter coil in the Milliwatt range. Thus not as a reception (!) coil for MW. It means it has to stray out that frequency on the MW band in the 3 milliwatt (energy) output range.
Much more is explained in the video.
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Upload 26 January 2025, update 30 jan. 2025.
Music: "Where I am from", Topher More and..
"In Albany New York", by the 126ers
It is copyright free music from YouTube