A question for Harry... if I can

Hi Andrew,
IMHO the idea has several merits, especially dividing the drift to get a more stable oscillator.

My experience is that oscillators at higher frequencies are more susceptible to drift than low frequency oscillators, but as always, an oscillator is limited by temperature and mechanical constraints. If it is well mechanically designed then, then you can tolerate 10x more drift due tot he divider, so it could be a good idea. The only way to tell is to "suck it and see".

I have built a load of VHF FM "bugs" and frequency stability was always a problem. At 5MHz the capacitances are high, but at VHF the capacitances are so low that proximity to hands and other metal bits change the frequency. Look at my FM Bug V5, and there you see that I solved the mechanical stability issue by fabricating the coil on a PCB. I had to use a second RF amplifier that did not amplify at all. The load on the oscillator had to be kept constant, otherwise the antenna changed the frequency dramatically, so TR3 is only a 0-gain buffer to get better frequency stability.

For HF one can always wind coils on ferrite rings, and the closed magnetic loop increase stability a lot. Perhaps it is possible to make a 50MHz oscillator on a ferrite bead. That would dramatically reduce inductive effects due to proximity. You would also need some good quality NPO caps. If you use a variable capacitor to change frequency then it would be a good idea to physically mount it in a metal box, with the rest of the oscillator, to eliminate capacitive changes do to proximity.

One small tip, when I played with 145MHz I once made a tuneable 2m NBFM receiver. That suffered a bit from drift with temperature. I replaced the copper oscillator coil with tinned iron wire, as is often used for resistor leads. That helped a lot.

Thank you very much for sharing this idea with us. I think it is an exciting idea and with a little thought for design, it could be really practical. The challenge would be more mechanical than electrical. Please let us know how you get on with it.

Very best regards from Harry - SM0VPO

First of all. thank you Ivan for the reply and for telling me that the idea isn't just a brain fart (at 60, and after a hearth attack and a brain stroke, I'm not exactly in mint conditions ), also thanks to Ruud, but I think he did't understand my idea, so I'll try to expand it a bit

Let's say we want to build a VFO for the HF Ham bands (or part of them); now the idea is to build an oscillator (VFO in this case) working at a frequency which is above the top frequency of interest (I used 40 to 50 MHz in my example, but willing to cover the ham bands from 160 to 40 meters, the oscillator may work at 20 MHz or so); anyhow, such an oscillator may then have some drift, so we use a divider which, not only will bring the oscillator frequency down to our desired range, but at the same time will reduce the drift to a negligible level

Usually the percentage of drift won't change very much if you change the frequency of an oscillator.
So if the drift is 1 KHz at 50 MHz, there is a good chance that the drift will only be 100 Hz if you build a 5 MHz oscillator... (Advantage: no divider needed!)
The absolute drift will be less, but the relative drift will be (almost) the same!

Hi Andrew,
it is not crazy at all. There is nothing fancy about a frequency divider by 10. A divider by 8 or by 16 would be even simpler. Not every type is able to work up to 50 MHz, this may be limiting a bit. It would produce a square waveform full of harmonics of course, so a sharp filter might be needed for certain purposes to get rid of them. But the harmonics do not matter at some mixers etc.

VBR from Ivan

It's just something off the top of my head, so it's probably a crazy idea but...

let's say we build a reasonably stable VFO, say in the 40 to 50 MHz range, now, despite our efforts, the VFO has (say) some 1KHz shift due to heath and/or other factors

Now let's say we connect our VFO to a converter, so that the output frequency of the converter will be 1/10 of the one from the VFO, so in the example we would have an output frequency ranging between 4.0 to 5.0 MHz

now, if our VFO shifts by 1KHz, the resulting output shift would become 0.1KHz, that is, negligible

My question is (are ) it is viable ? And if so, willing to build something like that, how would you design it (not my cup of coffee, as you understood )