Communication Concepts FL1 Low Pass Filter - Manual (Page 2)

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Table 2 – Parallel Capacitance Values
Desired Value Parallel Values
BAND C1, C2 C1A C1B C2A C2B
(meters) (pf) (pf) (pf) (pf) (pf)
160 1653 1500 150 1500 150
80 847 820 27 820 27
40 470 470 -- 470 --
20 240 240 -- 240 --
15 161 110 51 110 51
10 117 100 18 100 18
Construction Hints
The effective inductance of a toroid coil depends in part on the distributed
capacitance between the coil turns and between the ends of the winding. The
distributed capacitance should be kept as low as possible. The pictorial
illustration in Figure 2 show the inductor turns distributed uniformly around the
toroid core, but a gap of approximately 30 degrees is maintained between the
ends of the winding. This method is recommended to reduce the distributed
capacitance of the winding. The closer the ends of the winding are to one
another, the greater the unwanted capacitance. Also, in order to achieve the
desired toroid inductance, the winding should be spread over the core as shown
in Figure 2.
Figure 2 – Toroid Winding Pictorial