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8.3

RF characteristics of various types of winding

Figure 13 shows the relation between the impedance and the frequency for two chokes of equal in-

ductance. One of the chokes has a two-layer winding and the other is randomly wound. The choke

with random windings has a considerably higher first resonance frequency. The spurious resonanc-

es are very much higher than 10 MHz. The impedance at frequencies above the first resonance fre-

quency is approximately five times higher. This leads to better interference suppression at high

frequencies.

Fig. 13

Impedance |

Z| versus frequency f

comparison between two-layer winding and random winding

The RF characteristics of all chokes supplied by EPCOS are within the specifications and reproduc-

ible, as the winding processes which we have developed for single-layer, multilayer and random

winding ensure that the characteristics of the inductors produced display very little variation.

The reproducibility of electrical characteristics of chokes is mainly determined by the production

technique used. At EPCOS, coils are wound mainly by automatic machines (either fully or semi-au-

tomated). This permits even complicated winding patterns to be produced in large production runs

with very little variation in product characteristics. In fig. 14, the impedance curves of several

chokes, some wound manually and some by machine, are shown for comparison. With the random

winding used in this comparison, the advantages of machine winding are clearly noticeable.

Random wdg.

2-layer wdg.

General Technical Information