Sverre Holm writes:
There are several low power transmitters around that can be purchased, but most of them only cover the mediumwave band and not longwave (153-279 kHz). Further they are quite complicated as the frequency necessarily has to be user settable.
I looked for a simpler way to make a single-frequency transmitter and found that the function generator chip XR-2206 which I happened to have in my junk box could both generate this frequency and do the amplitude modulation. The RC-oscillator seems to be stable enough for this low frequency although I haven’t tested this much.
Here are the first results with images of the circuit on a Veroboard and the oscilloscope picture of the modulation with my Tandberg TP41 70’s radio on top of it listening to Dire Straits from Spotify streaming over longwave.
The circuit has very little output power, lacks antenna tuning and harmonic filtering, so there is room for improvement, but at least it works.
More details at LA3ZA Amateur Radio blog.
Hi from Italy! I’d like to find a low power lw transmitter.
You are a great! In the next days I’ll try to build it