[ARC5] Making Stable Inductors for 2 MHz

[Kenneth G. Gordon]

On 29 Jun 2011 at 10:13, J. Forster wrote:

> Do you know if it makes much difference whether the winding is a single
> layer solenoid, or if it needs to be like IF transformers, as long as
> the self-resonant frequency is high enough?

For frequencies down to 500 Khz, single-layer is both more stable, 
and more easily done. It is also quite, quite adequate. One other 
thing to keep in mind: the lower in frequency you build your VFO for, 
generally, the more stable.

If you are still very concerned about stability, you might consider 
building your VFO for 1Khz or even 500 Khz, then doubling or 
quadrupling.

One significant advantage to doubling is that the output of your VFO 
at the frequency of interest usually has no effect on stability 
caused by feedback to the input.

> From what I can see, most (toroid-cored VFOs) are not that good.

Yet, there have been many, many VFOs built using toroids, and almost 
all for higher frequencies, like up to 15 MHz, at least. The key is 
VERY low current through them, and minimal levels of RF.

Nonetheless, for your uses, I would avoid them. They are unnecessary. 
One of their most useful characteristics is their very small 
size...which in your case is not needed.

> > filament (heat) vastly reduces any thermal drift.
> 
> Understoof. I want to avoid any temperature control, hence the +/- 10
> C spec. I think, since the thing will eventually be in the center of a
> 50,000 ton ship, the temperature will be pretty stable.

I see absolutely NO PROBLEM with a simple, single-layer solenoid-type 
coil and variable capacitor VFO in that application.

Good luck, John.

Ken