ozQRP MST3 Construction And Operation Manual page 34

Bifilar transformer T5
Take a 500mm length of 0.4mm enameled
wire and fold in half. The wires need to be
twisted together. Following is a suggested
method:
Clamp one end of the doubled wires in a
vice. Make a loop at the other end and place
on a hook shaped bit in a battery drill.
While keeping the wires taut, run the drill
on slow speed until there are about 3 twists
per cm.
Carefully wind 5 turns on a FT50-43 ferrite
toroid trying to avoid scraping the enamel
on the sharp edges of the toroid.
Scrape some enamel off the ends and use a
multimeter to find the start (S) and end (E)
of each winding.
S1
Also check that there are no shorts between
E2
the two windings.
S2
E1
Take the end of the first winding and the
start of the second winding and twist
together to form the centre tap.
Trim the leads with side-cutters and tin
with solder before installing. Push the wires
through the holes in the PCB and sit the
toroid so that it rests against the surface of
the board.
S1
E2
Ensure the two-wire centre tap goes to the
middle hole of the T5 component overlay
S2 E1
closest to Q14.
MST3 Construction and Operation Manual – Issue 1 Page 34