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Hi again friends. This will be a little different than my
usual crystal sets projects. This time there is a cast of 3! Devin and Ian
came over to build a set with me. This project turned out well.
This radio is built like my #36 radio.
That is, a single coil and dual gang variable capacitor. It is a good design
with better performance than the standard single gang capacitor circuit that
is popular.
I first explained how radio works. Here is what I said. Lets say that
the two boys want to talk with each other. They might get a half a block away
and then they can't hear each other. They need some way to carry their voice
further. Audio frequencies don't carry well in air. However radio frequency energy does
travel a long distance. How about letting the transmitter carry the voice.
So the voice is added to the carrier. Since we can't hear radio frequencies,
we need a way to convert them back to the audio. The radio receiver is adjusted
so the resonance of the coil and capacitor together equal the frequency of
the radio frequency to be received. Think of blowing across a soda bottle.
You hear a tone. As the soda is consumed, the tone gets lower.
The radio, through the detection process removes the
radio frequency energy and leaves the audio. This is passed on to the earphone.
The first task is to wind the coil. Devin did the winding while Ian
kept count of the number of turns. He had a little difficulty as the slits
were quite narrow. It was mentioned that winding spider coils might be a
good way to relieve stress. After winding hundreds, I should be real
mellow now. :)
After the coil was wound it was time to take a trip to the shop
(my kitchen). The solder lugs were bent, the terminal screws and nuts
were tightened. Then the coil and capacitor were mounted.
The next step was to solder the wires and components. Following
the hand drawn diagram, we all took turns wiring the radio. Those boys
learned to solder real fast. Before testing, we went through the wiring,
step by step. I felt like Mr. Wizard!
Now for the test. Devin took the first listen. He heard one of
the local stations coming in well. We did find that the radio didn't quite
hear the highest frequencies, so a few turns were removed from the coil.
Additional testing was done.
Ian and Devin were excellent students. It was a pleasure to build
a radio with them. I hope that you will find the time to make a radio
with a younger person.
73 and good crystal DX. Dave - N2DS
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