I have been trying different
crystal radio designs, experimenting with crystal radios
lately and I decided to put
together something that would allow me to build these designs quickly and
easily using jumper wires
so I could test these designs because frankly I have found a couple designs
that do not really work very well
and so I am going to go through some of the popular designs on the Internet
and see how well they really work. This setup will allow me to put them together quickly
to show you what's going on you and wheter they work or not. The first one is a very popular design
it's got a variable capacitor tuner
Let me set it up and we'll
see how well it works. We can compare it to
this design which is the modified boy scout radio
and we can compare the two and see which works better
OK, let's get started
This is the setup, from our picture
you can see, we will check it, the antenna goes through the coil
to the ground. We have the antenna
connect on to the capacitor
antenna comes through here connects also to the coil
this is tapped to the coil right here and a
then goes across 80 turns, 20, 40, 60, 80 turns.
80 turns later goes to the ground which is this yellow wire
following colors: connect back here to the
and they also connect to ground, you can see ground
connects to the variable capacitor. The diode on the antenna side
here Comes through the insulator block
down here, connects here to 1 side
of the crystal earphone.
The other side of the crystal earphone goes back to ground okay
we got that covered. Now you listen while I tune through this
and you can hear what we get. <>
All I get is 1 station when I listen. I have gotten up to 2
stations but this is only 1. This is one of the most popular designs
This design you'll find all over the internet, it looks very good
but it plane doesn't work. I have tried many different configurations, using other coils
and other numbers of turns and so forth, other variable capacitors, bigger and smaller
and I get one or two stations at most
so it not working like I thought it would. I thought it would work like a transistor radio, I'd be able to tune the
variable capacitor
and I would get all the different stations and very clearly and
I've never have. Let me go through
a little bit why I think there's a huge difference between this
and some other crystal radio designs that work better
for example those with the wiper on them. OK, let's go over that
the you agree with me
Here's my theory on why these 2 crystals operate very differently, why this one
will receive... I've gotten 17 to twenty different stations on this one
and this one I get 1 or 2. Why is that?
My theory is, if we look at these,
If I take any coil, it has both induction and capacitance
and that's what creates that resonance thing and gives you the radio tuning
and what the wiper is doing is dividing the coil in 2 different parts
The left side has inductance and capacitance and the right side has its
own separate inductance and capacitance. As I move this
wiper the inductance on this side is getting smaller
and on this side it's getting bigger
And when I move it back this way the inductance and capacitance on this side is
getting bigger, hugely bigger and on this side it is getting much smaller
and I'm changing the inductance and capacitance
together so I'm getting this huge change in inductance and capacitance
which again is what causes that resonance thing
thing in the circuit which give me the radio
On this side, I got the first 80 turns like they told me they told me, I got it tapped here
I got the antenna here and the first 80 turns, like they told me
Here's the diagram. 80 turns
and that's it
There's nothing else, no wiper on there. I've got 80 turns and
I've got the inductance and capacitance
from those turns and that it.
and then I'm just changing the capacitance in the variable capacitor
across here, which is right here
and i'm changing the capacitance, BUT, all of this is fixed
there's no induction or capacitance changing here, so I'm only going
from about 0 to 360 pF and again no change in inductance
My guess is that's why this one picks up 1 station, and frankly I can get 1 station with a diode, antenna and ground
So I don't need all this stuff. My guess is again that's why this setup
does not work nearly as well as this setup because
the I'm only changing a little bit of capacitance and the inductance and capacitance in the
coil stays fixed. Where on this side i change 2
So I get a whole different change in the set of inductances and capacitances, the left set and the right set
That is my idea why
this modified boy scout radio works
much better
and this diagram that you find all over the internet
I'm disappointed because I wonder how many people have given up on crystal radio because
they try to do this and it just doesn't work
That's it for this setup. I mean
this plain doesn't work very well and
I would discourage people from trying it. I'm not the only one who posted
on the internet that this thing doesn't work well
but hopefully people will see this style
and build it and have a lot more success with it.
That was it. Hope you found it interesting and useful in your
crystal radio building