The optimum Q (quality or magnification) of an assembly is found in balancing the fundamental physics of both the core material and the winding. The assembly's contribution to superior Q is found in the core materials shape, inductance and frequency sensitivity. The windings contribution is maximized by minimizing frequency specific wire losses in the winding. The key to optimizing the Q of the assembly is selecting the proper core material, wire and winding characteristics for a particular frequency .


The iron powder and ferrite materials used in Lodestone Pacific's Shielded Coil Forms are formulated for optimum Q within a specific frequency range as shown by the table on Page 2. Q vs. frequency curves show the highest Q's achievable for a particular core material and frequency.

The shape and magnitude of these curves can be characterized by the following formula:


Where f is frequency in Mhz, L is inductance in µh and R is the effective series resistance due to both copper and core loss in ohms.

While the frequency and inductance is known or calculated, the frequency sensitive copper and core material losses are often difficult to calculate. In addition, variations in core material density and winding characteristics often make the Q experienced in actual applications differ from theory.

The Q vs frequency curves included in this catalog are plotted on a semi-log axis and were derived from actual testing of the variable assemblies in a parallel resonant circuit and reflect the expected Q readings with a specific inductance and winding. As the frequency is varied, the readings will trace a humped curve identifying the optimum inductance-frequency balance that produces the highest Q. Increasing inductance by adding turns of wire or tuning the core towards the maximum position will create a new Q curve with a peak that will be shifted down in frequency. Conversely, reducing inductance by decreasing turns or de-tuning the assembly will shift the Q curve peak towards a higher frequency.


Figure 3 shows the L57-2-PCT-B-4 assembly wound with a decreasing numbers of turns. The family of Q curves show the trend towards higher frequency Q curves as you reduce inductance by reducing turns. It also shows that the maximum value of each Q curve will diminish as the curve peaks move to the extremes of their recommended frequency ranges. There is an optimum frequency and inductance for a given assembly where the "peak of the peaks" will occur (at 1.5 Mhz in Figure 3). This is why applications requiring high Q are best engineered with the inductive portion of the tuned circuit optimized first, and the capacitor specified to support that optimum Q.

Each core material formulation will produce similar families of curves within their optimum frequency ranges. The complete family of Q curves for the L57 series show that mix formulations 7 and 6 exhibit better Q characteristics as the frequency moves above formulation 2's optimum frequency range.

The amount of core material in the assembly will also improve Q. As an example, the L57-2-CT-B-4 wound with 25 turns of 15/44 Litz wire will produce higher Q's than the L45-2-CT-B-4 with the same winding. This is due to the 28% more iron powder in the larger L57 shielded assembly. Comparing the L31-2-CT-B-4, L33-2-CT-F-4 and L43-2-CT-F-5 shows the relative Q of these assemblies with 25 turns of 15/44 Litz wire at approximately 2 Mhz.

In comparing these curves it can be seen that increasing the amount of core material also shifts the "peak of peaks" down in frequency. As an example, the L57-2-CT B-4 (4.45 grams of core material) with 25 turns of 15/44 peaks at 1.5 MHZ, while the smaller L33-2-CT-B-4 with the same winding and only .601 grams of core material peaks at 2.3 Mhz.

Figure 3




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