From mboxrd@z Thu Jan 1 00:00:00 1970 From: Geoff Bagley Subject: Gyrators. Date: Tue, 01 Dec 2009 13:33:21 +0000 Message-ID: <4B151B21.4040802@btinternet.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-hams-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Linux Hams 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