ozQRP MST3 Construction And Operation Manual page 33

Step 12: Coils
Choke
Install the RF choke in the same manner as for
the resistors.
Transformer T1
Take two 80mm lengths of 0.4mm enamelled
copper wire.
Wind 4 turns for the primary (bal mod) on a
FT37-43 ferrite toroid.
Then wind 3 turns for the secondary (xtal
filter).
Scrape the enamel off the ends of the wires
and tin with solder before installing in the
PCB.
The winding direction is not important.
Transformers T2, T3 and T4
Take an 80mm length of 0.4mm enamelled
copper wire and wind the 3 turn secondary
on a FT37-43 ferrite toroid.
Take a 150mm length of 0.4mm enamelled
copper wire and wind the 10 turn primary.
Scrape the enamel off the ends of the wires
and tin with solder before installing in the
PCB.
The winding direction is not important.
MST3 Construction and Operation Manual – Issue 1 Page 33