Lawrence A. Pizzella
a.k.a. Loose
Coupler
Most
Rockheads would agree that when the bug for building crystal radios
has bitten, you develop a thirst to make them out of anything you can
get your hands on. As the thirst grows stronger, more and more unlikely
items begin to look like the elements for the next Crystal Set.
Visualize this dedicated builder
as he surveys the various items around the house. Empty Coke cans morph
into variable capacitors, toilet paper rolls and almost anything cylindrical
morph into coil forms, old razor blades and rusty nails morph into detectors.
In recent months I noticed that the small plastic caps from my mineral
water bottles kept morphing into tuning knobs, and larger plastic lids
morphed into earphones. Perhaps it was all a mirage brought on by the
insatiable thirst to build that next Crystal Radio.
Well enough already! The thirst
must be quenched, and Gatorade is just the ticket!
The
Gatorade Radio has satisfied my thirst and stopped my hallucinations,
--at least for now. The circuit is a classic double tuned Loose-Coupler
wound on Gatorade bottles. A 10-220 pF poly Tuning capacitor from the
Electronics Gold Mine is glued into the lid and Calistoga Mineral Water
caps serve as the tuning knobs. To cover the band the coils are about
400uH. 65 turns of #28 enameled wire, space wound over the ribs of
the plastic Gatorade bottle does the trick. I can tune KSFO (right-wing
talk radio) in the North Bay at 560 kHz, and KLIV (CNN Headline News)
in San Jose at 1590 kHz. Tuning is a bit tight at the high frequency
end, but no tap changes or switches are needed. Be sure to set the
trimmers on the Poly Caps near minimum. I used double-sided plastic
carpet tape on the ribs of the bottle to hold the windings in place,
and to reattach the Gatorade labels. The detector bottle has a small
10-turn coil near the bottom that can be used for antenna coupling if
a single tuned configuration that uses only one bottle is desired.
The
detector diode has a notable history. I had already started to scrounge
parts while still in the Navy in the early 70’s. I would visit Mike
Quinn Electronics in Oakland looking for interesting stuff. He had
piles of old PCBs that I liked to sort through. Some boards had DTL
logic chips (Yes DTL!) which I found useful for repairing logic boards
used in some of our shipboard equipment. Also amongst these treasures
I found several boards loaded with germanium diodes, so a grabbed ‘em
looking forward to the day I might use them to build a Crystal Set.
Almost 30 years later one of them has found a home. Snips of PCB and
bits of wire for the Antenna, Ground, and Earphone terminals complete
this minimalist design.
But
the main reason for making a Crystal Set out of Gatorade bottles is
to showcase my home made earphone housed in two Gatorade lids. This
earphone is a low impedance type, so it requires a matching transformer.
(drats) It too is made of only bits of wire, plastic, and glue. (…and
a magnet.) Sensitivity and fidelity is a bit low now, but I have plans
for improvement.
When
used with a good set of phones, all the Bay Area stations are easily
heard and separated. I took this radio to the Museum of American Heritage
in Palo Alto, CA last week to show the kids who were there for our Electrostatics
class. The kids really thought it was “cool”. I do too.