Communication Concepts FL1 Low Pass Filter - Manual (Page 4)

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The capacitors C1 (or C1A and C1B) and C2 (or C2A and C2B) should be
mounted on the PC board first. Refer to Table 2 for the proper values and the
component layout pictorial in Figure 4 for proper placement. Next wind the toroid
with the proper number of turns using the #18 AWG enameled wire included.
The wire should follow the contour of the core and be snug. Refer to Figure 2 for
the proper number of windings and the construction hints for the toroid winding
procedures. After winding the toroids, scrape off enough of the enamel coating
on the wire for soldering purposes. Then mount and solder the toroid to the PC
board. The toroid is mounted to the PC board using a 4-40 x ¾ inch bolt and
KEP nut with a large fiber washer. Refer to the toroid mounting pictorial in Figure
5.
Figure 5 – Toroid Mounting Pictorial
Since the filter circuit is symmetrical, the input and output can be reversed. 50
ohm coax should be used for the connections as shown in the component layout
pictorial in Figure 4. The shield of the coax should connect to the large ground
foil on the PC board. The filter should be connected as close as possible to the
output of the power amplifier. This distance should be 6 inches or less. Connect
the filter between the output of the amplifier and the antenna as shown in Figure
6. No tuning of the filter is necessary if care is exercised in the construction.
Figure 6 – Filter Installation