Page 322 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

+V
IF Тгапsfогmег
1 8 4
С

.1 uf J IF Signal

А ~ 1

Т2

СсЬ

IF Transforme,r

1
~ 2 го
О1
+Vbias
~ (е .g .. 2NЗ904) VE
т-
4 9
Т1

RE

Note: Each IF Тга пsfогmег has ап i пtегпаl capacitor.
FIGURE 17-28 Ап IF amplifier with the coll.ector not connected to the tap
of the primary winding.

А typical 455-kНz IF tгапsfогmег has ап iпtегпаl геsопаtiпg capacitor of about 200
pF. Theгefoгe, the Q of the coil is
Q = (2п455,ООО Hz)RC = (2п455,000 Hz)R(200 pF)
if R = 200 k

, thеп Q = 114. If R drops to 163 k

, then Q = 93, and if R drops to 67 k

, then Q = 38.
As сап Ье sееп, соппесtilпg the collector of the tгапsistог to а tap оп а tapped
winding has ап аdvапtаgе of miпimiziпg Q losses. Also recall that а IOS5 ilП Q of the
coil results i п роогег 5electivity апd IOS5 of gаiп.