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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, Bi-filer 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.
When tining the leads for
T2, make sure the insulation doesn't melt too far up the wire, as the two windings could short
together.
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L4, L5 T50-2 core (large, red) 22 turns, # 24 wire. (16”) Evenly space turns around core,
leaving small gap at wire ends
●
T1 – FT50-43 core, (large, black) 5 turns, # 24 wire, bi-filer. (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 left..
●
T2 – FT37-43 core (small, black) 5 turns, #24 wire, bi-filer. (6”) As with T1, fold wire
in half and wind 5 turns. Identify wire ends and arrange opposite each other as with
T1.
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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.
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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.
●●
T4 – T50-7 core (large, white). Wind 21 turns #24 wire. (15”) This is the primary winding. Next wind 8 turns (6”)
in the gap between the primary turns. This is the secondary winding. Make the windings are snug to the core for
stability, but still loose enough you can move them slightly to adjust the spacing.
●
Install the T4 primary winding (outside wires) in the pads labeled “P” and the secondary (inside wires) into
the holes labeled “S”.
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Picture 2, wound toroids
Picture 3, tinned wires