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Larry Venick (Elvee)
New member
Username: Elvee

Post Number: 1
Registered: 3-2010
Posted on Sunday, March 14, 2010 - 6:36 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Having my Cub Scout den build crystal radios next week. At first I was going to have them build the "quick & simple" radio, but the idea of making the tap loops in the coil and stripping them seemed a little tedious (I'm pre-making the coils and I need enough for 11 kids)

I took the design of the "10 Minute Radio", but instead of using the ferrite-loop antenna coil, decided to stick with the wound coil - minus the taps - thinking the variable capacitor would be able to tune in stations.

I made a prototype today. Coil is 24awg coated wire - 100 wraps on a 2 5/8" mailing tube. Antenna is 100' of 24awg coated wire.

I hooked it up and it works - clearly picks up 710khz which is a 50kw clear channel station. However; that's the only station it picks up - even turning the dial on the capacitor. There are 2 other 50kw clear channel stations nearby -660 & 770.

Here is a picture of the prototype. Alligator clip on right goes to antenna, one on left to ground.

Is there any way I can get this to tune in other stations?
radio prototype
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Larry Venick (Elvee)
New member
Username: Elvee

Post Number: 2
Registered: 3-2010
Posted on Sunday, March 14, 2010 - 8:20 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Addendum -

Did some googling and came up with something......

Attached the antenna to the third tap down from the top (30 wraps), and added a 47k resistor across the earphone. Now, when I turn the capacitor all the way to the left I start to get a faint, second station.

Are 100 wraps too many for this coil/capacitor combination? Like I said, I'm using 24awg coated wire.

I also have some 28# magnet wire and smaller diameter tubes (pvc, actually) - 1" and 1-1/2" OD I can use.

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