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Skywave · 6th Feb 2009, 10:52 am

My first thought is that the types of coils you are using are unsuitable. It sounds at though as the freq. is raised, the feedback to maintain osc. is decreasing right up to the point where there is inadequate feedback to maintain oscillation. This is probably caused by low Q of these coils: the amount of feedback is largely determined by the dynamic impedance of the tuned cct. (which is freq. dependant), which itself is a function of the Q of the inductors. Air-spaced and ferrite / dust-iron cored coils are preferable in this type of application; they will have a higher Q.

HTH

Al /Skywave.

6th Feb 2009, 10:52 am	#7
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Signal generator problems My first thought is that the types of coils you are using are unsuitable. It sounds at though as the freq. is raised, the feedback to maintain osc. is decreasing right up to the point where there is inadequate feedback to maintain oscillation. This is probably caused by low Q of these coils: the amount of feedback is largely determined by the dynamic impedance of the tuned cct. (which is freq. dependant), which itself is a function of the Q of the inductors. Air-spaced and ferrite / dust-iron cored coils are preferable in this type of application; they will have a higher Q. HTH Al /Skywave.