AD 9851 variable frequency oscillator 1 Hertz stabile (software driven)
An old video from my former channel, Radioam232. It shows a chip from Analog Devices with which you can make a VFO/local oscillator for short wave (1-30 MHz, as far as I could see). The chip has an extreme good stability. A computer interface is necessary to drive this chip, also software. The software to drive this chip on 1 Hertz exactly is available (free) on the internet. Don't ask me where and don't ask me for the oscillator circuit (sorry), but I am (almost) sure all circuits are available on the internet. You can combine this extreme stabile oscillator with the simple radio circuits published in my books (Retro Radio, Dutch text) and "2-10 MHz radio receiver and 1 transistor VFO's" (English text, author Ko Tilman). The latter circuits can be upgraded by the most recent local oscillator circuits that I have uploaded on YouTube (29 july 2012), but with this chip these upgraded circuits can bet set aside. Though the great advantage is that these upgraded VFO circuits work without a computer (...). Adapt the antenna coil/antenna tuning capacitor for the higher frequencies that this chip (or analog HF oscillators) can generate, less turns and a smaller tuning capacitor are necessary to get to frequencies between 15 MHz and 30 MHz.