The Experimental Radio Project

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This is an account of how a radio project evolved into something different then what was intended. It's merely presented for your entertainment. I don't recommend you build this set, it doesn't work all that well for the amount of work involved, though it is fun to operate and is extremely selective if you don't use a ground connection. If you want to build a set, look at the Ferret Ferrite pages on this site.
TRF radio
The experimental Tuned Radio Frequency receiver.

Radio Craft cover

Some time in 2012 I obtained a copy of the October 1929 issue of Radio Craft Magazine. On the cover is Lee de Forest, the inventor of the triode vacuum tube. He is holding the invention in the illustration.


This device, named the "Audion," made modern electronics possible. It was the first triode vacuum tube, patented by Lee de Forest in February of 1908. 

On page 174 was found "The Cooperative Radio Laboratory" which was a monthly feature. On page 175 was an interesting schematic.  (See full article here.)

radio schematic
What interested me was the "TANDEM TUNER," but then I saw, right at the top center of the schematic, a crystal diode! This was  a crystal set with radio frequency and audio amplifiers. I decided I'd build a modern version with transistors instead of vacuum tubes.
It should be (have been) a piece of cake!
TRF tuner
The TANDEM TUNER. Notice, the article states, "a selectivity design  the regular set builder will do well to observe."

radio coils
There were three coils needed. The coil data is shown in the diagram, and a drawing of the coils was conveniently provided in the illustration of the TANDEM TUNER. The only change made was to use 75 turns of wire instead of 90, and .00039 variable capacitors as opposed to the .00035 used in the article).  I used 26 gauge wire.
Parts were ordered from various online sources and work began on the coils. 2" cardboard tubes were cut and polyurethaned, the coils were wound and then polyurethaned again.

radio coils
A team of Celestial Mechanics worked tirelessly to create these beautiful coils.