Gyrators.

[Geoff Bagley <geoff.bagley@btinternet.com>]

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