Project XTAL Radio – Assembly
Tools:
Needle nose pliers
knife
sandpaper
wire cutters
screw driver
Construction Procedures:
A
variable capacitor
is used in most AM/FM radios to tune in different radio stations. Changing the
capacitance will change the frequency of the tuning circuit. On most radios this will be the “tuning” knob or
“tuning” controls. A simple capacitor consists of two metal plates insulated from each other. The capacitor and
coil work together as a tuning circuit to select the desired station for reception. A second variable capacitor may
be needed to regulate the coupling of radio signals from the antenna to the tuning circuit. Construction for both
capacitors is the same. The tuning capacitor is designated as “
C1
” and the coupling capacitor is designated as
“
C2
” in the schematic diagram.
Building the capacitor:
1. Cut the paper or transparency film to a
size of 8 ¾ inches long by 5 inches wide.
2. Cut a piece of foil to a size of 8 inches
long by 2 inches wide
3. Carefully attach the foil to the
transparency 1 ½ inches from the bottom
of the transparency using the clear
mailing tape
BUT
leave ½ inch of one
end uncovered.
4. Cut a 10” piece of hook-up wire, remove
1” of insulation from each end and tape
one end of the hook-up wire to the
uncovered end of the foil. Make sure
there is a good connection between the
section of bare wire and the foil.
5. Wrap the foil-transparency assembly,
foil side out, snuggly around the can and
secure with the tape. The assembly will
slide up and down over the can
functioning as a tuning capacitor.
