[PJL]

I have decided to stick with the 50 turns as it covers much of the MW band that still has stations on it. I also managed to find a plastic container of the right diameter to saw up and have constructed a tidier coil with spacing between the layers of around 1.5mm.

This performs much better than my first attempt where layer spacing would have been much less. The test comprises a scope across the coil and light resistive coupling (82K) to a siggen. Not ideal as the probe capacitance will mess it up but good enough for comparison.

I am going to build one further coil, this time with a single layer of finer wire. The theory being that increasing the layer spacing will move the outer layer further from the variometer ring limiting the inductance range assuming that the ring works by reducing the effective area of air it is enclosing.

Once I have built the third coil, I will do some more controlled tests and decide on the best way forward. I will space the secondary out as far as I can and use a finer gauge wire as the resistance should not be critical.

For LW, Litz wire and wave winding will be required to keep the coil compact whilst minimising inter layer capacitance. I am not sure it is required for MW and was not used on the V1 which used cotton insulation so probably a finer gauge than I will be using.

Radio waves are remarkable things, I can 'tune in' a station on the scope even with this crude setup.