Toroidal coils:
Now the fun part – winding the toroidal coils.
Picture 2 shows properly wound coils. Note how the wire is made to
conform closely to the core. Winding the wire loosely around the core
is not only sloppy, but will not work properly. However, you don't want
the wire to be too tight, just snug.
Before winding the wire on the white core used for the VFO, it helps to
stretch the wire slightly by grabbing both ends with pliers and giving
them a little tug.
Coils shown left to right: VFO coil, Bifilar T1, LPF coil L4
Picture 3 shows how the wire ends need to be trimmed back and tinned before the coil is inserted into
the board. Putting a little blob of solder on the tip of your iron and then gently rubbing it against the wire
will melt through the insulation and tin the wire.
Trying to solder to the wire after it has been inserted into the board holes without tinning will not work,
as the pad and connecting tracks will wick away too much heat. Using enough heat to melt through the
insulation in that case can damage the board. A common mistake is to tin the wire, but not close
enough to core, so when mounted, the insulated part of the wire is in the hole and not soldered to, while
the tined part is actually snipped off.
●
L4, L5 T50-2 core (large, red) 22 turns, # 24 wire. (14”) Evenly space turns
around core, leaving small gap at wire ends
●
T1 – FT50-43 core, (large, black) 5 turns, # 24 wire, bifilar. (8”) Fold wire in half and
lightly twist together. After winding, snip wire where folded to separate ends. Use
ohm meter to identify the common ends of the two wires. Arrange the common ends
to be opposite each other on the core as shown in the diagram to the right.
●
T2 – FT37-43 core (small, black) 5 turns, #28 wire, bifilar. (6”) As with T1, fold wire in
half and wind 5 turns. Identify wire ends and arrange opposite each other as with T1.
The wires on T1 and T2 are now orientated properly and are symmetrical in respect
to the pad locations on the board. If the wire ends are not properly located, the
transmitter will not work.
●
Install L4, L5, T1 and T2 as shown in placement diagram below. Before placing T1 and T2, double check that the wires going in to
the A-A' pads have continuity with an ohm meter, indicating they are the ends of the same wire.
●●
T5 – T50-7 core (large, white). Wind 21 turns #24 wire. (14”) This is the primary winding. Next wind 8 turns of
#28 wire (6”) in gap in between #24 wire ends. This is the secondary winding. Make the winding snug to the core
for stability, but still loose enough you can move them slightly to adjust the spacing.
●
Install T5 the primary winding (21 turns) in the pads labeled “P” and the secondary (8 turns) into the holes
labeled “S”.
11
Manual revised 20160229
Picture 2, wound toroids
Picture 3, tinned wires
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