17-11-2012, 01:19 AM
May I contribute to this fascinating thread, please?
My researches have produced the following summary.
In variable tuning systems, permeability tuning offers considerable advantages in the maintenance of correct L/C ratios of the various tuned circuits and also allows for a closer aerial coupling to the first tuned cct. Since the tuning is achieved by adjusting the cores of the coils by a thread, a high degree of band-spreading or fine tuning is possible. Permeability tuning found favour in the design of car radios mainly on two counts: (a) the improvement in stability of the oscillator - the tuning coil was far less prone to vibration and mechanically 'going off tune' than a variable capacitor - and (b) the relative ease of designing a mechanical system for push-button tuning, enabling an exact adjustment to the required station. The increased gain available by closer aerial coupling was also of value in a car radio, since received signal strengths were then low, compared to those present at the typical domestic wireless installation, using variable-capacity tuning.
Al. / Nov. 17th., 2012 //
My researches have produced the following summary.
In variable tuning systems, permeability tuning offers considerable advantages in the maintenance of correct L/C ratios of the various tuned circuits and also allows for a closer aerial coupling to the first tuned cct. Since the tuning is achieved by adjusting the cores of the coils by a thread, a high degree of band-spreading or fine tuning is possible. Permeability tuning found favour in the design of car radios mainly on two counts: (a) the improvement in stability of the oscillator - the tuning coil was far less prone to vibration and mechanically 'going off tune' than a variable capacitor - and (b) the relative ease of designing a mechanical system for push-button tuning, enabling an exact adjustment to the required station. The increased gain available by closer aerial coupling was also of value in a car radio, since received signal strengths were then low, compared to those present at the typical domestic wireless installation, using variable-capacity tuning.
Al. / Nov. 17th., 2012 //
