Communication Concepts EB27A Construction Hints - Manual (Page 2)

BROADBAND TRANSFORMERS
Just a quick word about the broadband transformers. The low impedance winding of the
input (T1) and output (T3) transformers consist of one winding. Two metal tubes form
the low impedance winding. The tubes are electrically shorted on one end by a piece of
copper-clad laminate (PC board) with holes for the tubes. The tube ends are soldered to
the copper foil. A similar piece of laminate is soldered to the opposite ends of the tubes
and the copper foil is divided into two sections, thus isolating the ends where the primary
connections are made. The high impedance winding is formed by threading Teflon
insulated wire through the tubes for the required number of turns. The transformers are
loaded with ferrite material to provide sufficient low frequency response.
PC BOARD ASSEMBLY
Flow some solder (a very light coat) on the PC board where the input end of T3
will be mounted and install the chip capacitor, C5. See Figure 1.
Figure 1
Strip the leads of the output transformer (T3) to ¼ inch of insulated wire from the
transformer end.
Place the leads of T3 into the proper holes on the output side (the transformer
must be installed with the wide gap on the input end placed down on the PC board).
Place a piece of Mylar, Teflon, or similar piece of insulating material under the
transformer, T3 to prevent it from shorting to the ground plane. Position the transformer,
T3 close to the chip capacitor, C5 on the input end of the PC board. Solder the split-
ends (two places) to the PC board with a fillet of solder (make sure the transformer is
held flat against the PC board). See Figure 2.
2