Here is a design for a GDO by G3TYJ. I built this way back in the 1970's: it worked very well.
[attachment=8185]
Note that it does not use a centre-tapped inductor: it uses, if effect, a centre-tapped variable capacitor. Now theoretically, that variable capacitor could be replaced by a single-gang capacitor with a centre-tapped coil. The snag with that approach is that you would then need a variable capacitor that was exactly physically and electrically symmetrical with respect to R.F. ground. The nearest you could approach to that would be to carefully arrange the mechanical layout to provide that symmetry, probably with some compensating parallel capacitance. All-in-all, a lot of trouble to go to: hence a split-stator cap. and a two terminal coil: a centre-tapped coil to R.F. ground and a earthed-rotor capacitor is equally unnecessary and undesirable: one or the other, never both.
Al. / June 12, 2013 //
[attachment=8185]
Note that it does not use a centre-tapped inductor: it uses, if effect, a centre-tapped variable capacitor. Now theoretically, that variable capacitor could be replaced by a single-gang capacitor with a centre-tapped coil. The snag with that approach is that you would then need a variable capacitor that was exactly physically and electrically symmetrical with respect to R.F. ground. The nearest you could approach to that would be to carefully arrange the mechanical layout to provide that symmetry, probably with some compensating parallel capacitance. All-in-all, a lot of trouble to go to: hence a split-stator cap. and a two terminal coil: a centre-tapped coil to R.F. ground and a earthed-rotor capacitor is equally unnecessary and undesirable: one or the other, never both.
Al. / June 12, 2013 //
