Page 118 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

f S 5
2nd Oet,Ave, AF Amp

0.

3M .
J

x ,

L~;-l~ 67.?

M -lA ' BL -M 145
FI GURE 8-2B Schematic diagram of a four-tube radio.
Now let's turn to a block diagram of a typical transistor radio such as the Regency
TR-l (Figure 8-3).

Converter
RF Antenna Filter IF Filter 1 IF Amplifier IF Filter 2 Det
-7 ~ ~ ~ ~ t-
/
/
/
/
VC RF VC Osc
/ I"
+VC1RF +VClOS'
/ 140pf / 60 pt
Low Pass Filter 1/
~
I'
=~ Audio Couplfng Capacitor

Audio Amplifier
~
/

FIGURE 8-3 Block diagram of a four-transistor radio.
The built-in antenna coil and variable capaCitor VC_RF tune into a desired radio
station to produce an RF signal to the input of the converter circuit. The converter
circuit consists of a transistor oscillator circuit in which the oscillation signal is

combined with the RF signal. When the two signals, the oscillation signal and the
RF signal, are added together, the nonlinear characteristic of the transistor also
generates a multiplying action between the two signals. As a result, the output of
the converter circuit then produces signals that have frequencies of sums and
differences from the RF signal and the oscillation signal.

The output of the converter is connected to IF Filter 1, which only extracts signals
that are of the difference frequency. Further amplification of this difference