RE: [ScoutRadio] Crystal Radio Project
- When I was a child, I had a crystal set consisting of a germanium diode and coil of enamel wire about the diameter of a toilet roll. The enamel was sanded off just locally so that a variable pointer could make contact (i.e. a variable coil). That was it! A good antenna in the attic and a ground connection to the water pipes and my earphones almost deafened me.
73 AB2SN Christian
Date: Tue, 4 Oct 2011 18:49:54 +0000
Subject: [ScoutRadio] Crystal Radio Project
To all: I just uploaded a picture of a crystal radio project I'll be building with our scout troop at JOTA. It is a VERY simple, low-cost easy-to-build design.
The radio is built on an 8" piece of pine 1x6" plank.
The coil is build on a 5.5" square piece of cereal-box cardboard, with seven radial cuts down to a 2" circle in the middle. It is wound with 48 turns of 24 AWG enameled wire in a 'spider-web' style. A tap at 24 turns is also brought out. When done, a piece of tape is placed on each edge for reinforcement.
A 0.5" wide piece of corrugated cardboard is placed on two opposite edges on the bottom of the coil, and the coil assembly fastened to the breadboard using four thumbtacks in the corners of the coil board. The corrugated cardboard strips space the coil up from the board.
The radio is tuned with a 4" square piece of aluminum foil taped to the bottom of a 4"x6.5" piece of cereal-box cardboard, at one end, while 1/2" of the other end is bent up for a handle. This is slid under the coil.
At the opposite end from the slider, four #6 sheet metal screws are driven into the breadboard. Three have fahnestock clips, one just has a brass washer under its head.
The rightmost fahnestock has the coil center tap under it, stripped and tinned. This is the connector for a long antenna.
The middle fahnestock clip has the outer coil lead, stripped and tinned, under the clip. This is the short antenna connector.
The left fahnestock clip has the inside coil lead stripped and tinned, under the clip. This is the ground connection.
Between the short antenna and ground clips, a fixed capacitor is placed. Since this rig will only tune one half of the AM band, you should pick the cap to cover a strong local station. 68 pF will cover the high side of the AM band, 220 will cover the middle, and 470 will cover the bottom. Place the capacitor leads under the fahnestock clip.
A 47k resistor and leads from a ceramic (crystal) earphone go underneath the screw at the far left and the grounf clip.
A 1N34A diode bridges between the middle fahnestock clip and the far left screw.
Total parts cost will be about $5, and it should work pretty well with a decent antenna.
73 Dave NM0S