Hi.So I try several years to build a smal FM transmittet. I built mani small transmitters, but no one of them can't work stable. For example when I touch the device or move it, its frequency deviate (the frequency is not stable). The other problem is that there is many harmonics. Does anybody occupy in these kind of electronics ? Thanx.
I presume you're building single tansistor free-running VHF oscillators.
You won't get decent stability from a free-running oscillator much above
5MHz. Even at 5MHz, you still need to take great care, use high quality components - especially the inductor - and mount it in a screened metal box. Temperature variation is a major cause of drift. Even at 5MHz, designers need to select components that cause drift in opposite directions and thereby partially cancel.For stability at VHF: either use a PLL synthesizer; or a crystal oscillator and frequency multiplier chain. Hand-capacity effects are more significant at VHF because circuit capacitances are so small.
Yes the circuit have only one transistor. I don't want to use PLL sinteser because it need complex (difficult)circuit and components like IC. The other variant is to use quartz cristal oscillator at about 10-20 MHz, but it requires multipler and band filter on its output. I need some simple decision.
Any siplier circuit ? Did you think, that power amp with one transistor next to the oscillator, may enchance frequency stability ?
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