Page 78 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

wire a fruit/vegetable battery using two lemons or potatoes for this radio. Just be

sure not to eat (consume) any of the fruits or vegetables that are used for making
the battery.
In terms of construction, try to keep the base lead of transistor Q1 (MPSH 10) to the
Ll antenna coill's secondary lead short. The secondary winding of Ll typically has
about one-eighth the turns of the primary winding. Also, to avoid "recirculation"
from the a!mplified RF signal back to antenna coil L1, both inductors L2 and L3

should be mounted preferably at 90 degrees to the antenna coil.
This radio was deemed a "first" design, and one may wonder why the quotation
marks around first Well, Figure 5-1 really shows a fourth attempt to make a
successful radio working off low voltage (e.g., 1.5 volts). The first three designs
needed a minimum 2.4 volts and required more than two transistors.

RF Ant. Filter Two-Stage RF Amplifier f--- Det

VC &L1 01 &02 D3

+ 1.5

Rl
+ 1.S + 1.S
56K
C4 CS
+!
I ~
· L 1 Primary +t--m
VCl RF VC10se
470 uh 1 ut 1 ut
111 140 pf
60 pr
L2 L3
R2 R5 R7
1 mH 8.2 mH or HJ mH
6200 lOOK

03
2 .01 Uf t-- 2 =--.f
1 N34 or Germanium

01
R3 R4 R6
1 N914
2200 1!OOK 2200 Audio Signal
02
1N914

FIGURE 5-1 Block diagram and schematic of a TRF radio.
So what made this design in Figure 5-1 successful? There are two features. First
and foremost, it used inductive loading at the collectors of transistors Ql and Q2 to

raise the operating DC voltage at the collectors of these transistors. By raising the