MFT-20 DSB Transceiver Kit
Page 17
One turn more or less will affect the operation and the power output.
Toroidal transformer L7
L7 is an impedance matching transformer. An FT37-43 is used (black toroid with 9.5mm/0.375in OD). It
has a 10-turn primary and a 3-turn secondary.
- Take 17cm (7.5”) of 0.5mm diameter enameled wire and wind ten (10) turns on a black FT37-43
toroidal core. Spread the turns evenly around the toroid and wind them tightly so that so that they follow
the contour of the toroid and are as tight against the toroid as possible. The turns should be evenly
distributed around the circumference of the toroid. Leave pigtails of 10-20mm (0.70”).
- Now take about 8cm (3.5”) of 0.5mm diameter enameled wire and wind three (3) turns on the other
side of the toroid, spacing the turns within the space between the turns of the previous winding. Leave
pigtails of 10-20mm (0.70”).
- Before inserting them on the circuit board, use a cutter or sandpaper to scrape off the enamel from the
pigtails of the windings. Solder them in place. Mount the toroid with approximately 0.5 - 1mm distance
from the board.
- The ends of 10-turn winding to into holes “a” and “b” facing towards relay RL1. The ends of 3-turn
winding go to “c” and “d” facing towards L8 and C53 (place exactly as shown in the pictures).
Counting the turns: Count one turn for every time the wire passes through the center of the toroid.
