(28-11-2012, 05:44 PM)pwdrive Wrote: I did find a free Google book on the web about oscillators by Gottlieb where he mentions that two non-coupled coils can be used in the Hartley.
Lawrence.
The mode of operation of the Hartley oscillator: I looked it up in my copy of 'Electronic and Radio Engineering' by F. E. Terman. He provides an insightful analysis in which he shows that for zero mutual coupling between the two 'halves' of the coil, the circuit degenerates into a TPTG oscillator. Moreover, for the cct. to behave as a 'genuine' Hartley, there must be a mutual inductance between the two coils.
The 'Radio Engineer's Handbook', 4th. ed., (Langford-Smith), provides an equation which provides the minimum value of µ of the valve for oscillations, in terms of the circuit constants. That equation includes a term for the mutual inductance, M, between the two 'halves' of the coil. Substituting typical values for those constants into that equation, but setting the mutual inductance, M, to zero, it produces a very high value of µ. Moreover, as M is increased from zero, the required value of µ falls - and falls to a range of figures for µ that seem typical.
So, on the basis of those two entries (from gentlemen who know far more about this subject than I do), I submit that for a Hartley oscillator to be a 'true' Hartley osc., the coil must be tapped and a corresponding mutual inductance must exist between the two parts of that tapped coil.
Al.
