Gyrators.

I would like to hear from any other amateur who has experience with simulation of hi-Q inductors for use in VLF receivers by means of gyrator circuits.

There seem to be two sorts.

There is a simpler one which you can find in Wikipedia,
and there is a rather more complicated one by WB9ATW (taken from Ham Radio June 1979 ) which is to be found in the RSGB "LF Experimenter's Source Book 2nd Ed. Ed G3LDO.

This second circuit uses two op-amps rather than one (for the gyrator) and was used by N8BN in a receiver design published in the same publication.

I am interested in what Q-factor values are feasible, and the relative merits of the two circuit configurations.

It sounds nice to be able to vary the tuning of the circuit by means of a single potentiometer !

I imagine that if a very Hi-Q tuned circuit were to be made in this manner, you would have to drive it in such a manner as not to cause any appreciable damping, and consequent lower Q.

Any hints or experiences welcome. TIA.

73

Geoff
G3FHL