Recently I've been working on an AM transmitter for 40m. It occurred to me that FM should be much simpler to produce. I had ordered some varactor diodes recently and first tried to FM a crystal or ceramic resonator. I can't get much deviation and the audio did not sound good.
Then I remembered a post on Soldersmoke about a largely unknown but surprisingly stable oscillator called a Franklin oscillator. It has two transistors and has a very light load on the tuned circuit.
Rather than the variable supply transistor I fitted a 5V three terminal regulator. Coupled to the tuned circuit is a varactor diode with an electrolytic capacitor through which line audio is inserted. There's a trim pot to set the DC to the diode.
Initial results are quite promising.
The brilliant Charlie Morris, ZL2CTM, has an excellent video on the Franklin oscillator.
Thanks Stephen, VK2BLQ, for the tip.
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