Elecraft K2 Owner's Manual - Manual (Page 56)

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LECRAFT ® 55
Find RFC14’s component outline on the RF board, near the front
left-hand corner. Compare this component outline to Figure 6-15,
which shows two views of a typical toroidal inductor. RFC14 will be
mounted vertically as shown at the right side of the drawing, with one
wire exiting at the core’s upper left, and the other at the lower right.
There are pads on the PC board in these two locations.
Remove insulation
Figure 6-15
Note: Toroid illustrations such as the one above do not always
show the actual number of turns used.
To wind RFC14, cut a 9" (23 cm) length of #26 red enamel-
coated wire, then "sew" the long end of the wire through the core
exactly 10 times. Each pass through the core counts as one turn. The
finished winding should look very similar to Figure 6-15, but with 10
turns rather than 14.
Verify that the turns of RFC14 are not bunched together. They
should be evenly-spaced and occupy about 85% of the core’s
circumference. If the turns are all bunched together, RFC14’s
inductance value will not be correct. (Unless otherwise specified,
about 80 to 90% of the core should always be used.)
Stripping Toroid Leads
The enamel wire supplied with the kit can be heat-stripped. One way
to do this is to place a small amount of solder (a "blob") on the end of
your soldering iron, then insert the wire into the hot solder for a few
seconds. Another possibility is to burn the insulation off by heating it
with a match or small butane lighter for a few seconds, then use fine-
grain sandpaper to remove the enamel residue. Avoid scraping
insulation off with a razor blade, as this may nick the wire.
Strip and tin the leads of the toroid before you mount it on the
board. As shown in Figure 6-15, you should remove the enamel from
the leads up to about 1/8" (3 mm) from the core. You should see only
bare wire (no insulation) on the side to be soldered.
Install RFC14 vertically as shown by its component outline, near
the front left-hand corner of the board, then pull the leads taut on the
bottom of the board.
Solder the leads of RFC14. When soldering, make sure that the
solder binds well to the leads. If the lead appears to be an "island" in a
small pool of solder, chances are it is not making good contact.
Measure from pad to pad (not wire to wire) using an ohmmeter to be
sure the leads are making contact.
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Do not use adhesives or fixatives of any kind to secure
toroids to the PC board. Toroids will be adequately held to the board
by their leads alone. (T5 is the only exception.)