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 Post subject: Building a radio
PostPosted: Dec Thu 19, 2019 10:42 pm 
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Joined: Dec Thu 19, 2019 10:29 pm
Posts: 2
Hi,
I am attempting to make a homemade radio. I am using 22awg enameled wire and having a tough time
wrapping it around a cardboard oatmeal container. Does anyone know any techniques for doing that?
Also by having insulation on the wire (enamel or vinyl) wouldn't that prevent electromagnetic waves from radiating?
I understand that if you remove insulation the coils will b short circuiting but its insulation so why wouldn't that prevent
radio waves from radiating?
Thank You


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 Post subject: Re: Building a radio
PostPosted: Dec Fri 20, 2019 2:34 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 244
Location: New Hampshire, USA
You might try double sided tape on the drum. That will help prevent the coil from unwinding while you’re making it. I’d also recommend making a jig that will hold the oatmeal box/coil form stable and flat and able to turn on its axis. A handle to assist in the winding would be good, too.

No, the enamel coating on the wire will not prevent radio waves or magnetic flux from penetrating to the wire.


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 Post subject: Re: Building a radio
PostPosted: Dec Fri 20, 2019 3:27 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4084
Welcome to the hobby! This technique works well.

One end of the wire was tied to a chain link
fence. The other in was secured through two holes
punched in the coil form. The students pulled it taut.
Then they just rolled the cardboard tube
coil form toward themselves while
gradually walking toward the fence.

The resulting coils were wound beautifully. See here: http://www.tompolk.com/crystalradios/cedarcreek.html

Image


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 Post subject: Re: Building a radio
PostPosted: Dec Fri 20, 2019 5:56 am 
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Joined: Sep Wed 10, 2014 2:01 am
Posts: 2225
Location: Costa Mesa, California
The insulation on the wire does affect the characteristics of current flow--but the effect for your purposes is so little as to not be of concern. The electrons flowing in the wire can't penetrate the insulation, however the flow of electrons creates an electromagnetic field that the plastic insulation doesn't affect. If the insulation had a metal shield--then yes--it would prevent the field from penetrating and escaping. That type of wire is called shielded wire and is used for antenna feed lines or microphone wire or audio cable.

Norm

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 Post subject: Re: Building a radio
PostPosted: Dec Fri 20, 2019 12:00 pm 
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Joined: Jul Mon 26, 2010 8:30 pm
Posts: 28972
Location: Annapolis, MD
Brinks wrote:
Hi,
I am attempting to make a homemade radio. I am using 22awg enameled wire and having a tough time
wrapping it around a cardboard oatmeal container. Does anyone know any techniques for doing that?
Also by having insulation on the wire (enamel or vinyl) wouldn't that prevent electromagnetic waves from radiating?
I understand that if you remove insulation the coils will b short circuiting but its insulation so why wouldn't that prevent
radio waves from radiating?
Thank You

You stop "radio waves" only with a material that is either electrically or magnetically conductive. Electromagnetic radiation is a messy combination of electric and magnetic fields, with math that will cause major headaches. (Go to Wikipedia and look up Maxwell's Equations)

The over-simplified explanation: a changing electric field produces a changing electric field which in turn creates a changing magnetic field, which in turn creates........

An electric field cannot exist in a material that is electrically conductive---same logic for a magnetic field.

The biggest issue with the above gross oversimplification is that electrical and magnetic conductivity are a function of wavelength---which is why a piece of cardboard will stop light but have no effect on radio waves.

Did I OVER-answer your question?...;)

_________________
-Mark
"Voltage is fun to watch, but it's the CURRENT that does the work."


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 Post subject: Re: Building a radio
PostPosted: Dec Fri 20, 2019 3:52 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2118
Location: Monroe, NC 28112 USA
Macrohenry... Good idea for winding big coils for a first time project. I like the idea of laying-down a couple of strips of 1/2" Scotch double-side tape and always have handy a strip of blue painters tape to hold things if you need to take a break in winding.

If you don't have some way of controlling wire tension, you don't get good results... That is why I did make a simple winding jig so you have one free hand to control wire tension. But for a first effort, by all means think of going outside...

Robert


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 Post subject: Re: Building a radio
PostPosted: Dec Fri 20, 2019 9:29 pm 
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Joined: Dec Thu 19, 2019 10:29 pm
Posts: 2
Thank you so much everyone. Its been a big help.


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 Post subject: Re: Building a radio
PostPosted: Dec Fri 20, 2019 11:29 pm 
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Joined: Jun Mon 20, 2011 6:09 pm
Posts: 1174
Location: 56401
Quote:
Also by having insulation on the wire (enamel or vinyl) wouldn't that prevent electromagnetic waves from radiating?

That's actually a very good question, and has a somewhat simple answer.
The electricity flowing in the wire creates a field to exist around the wire. As Maxwell wrote in 1872 "It appears the energy is in the field around the wire and not in the wire itself".
That is why the insulation has no influence at all.

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Prediction is difficult, especially about the future. Niels Bohr


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 Post subject: Re: Building a radio
PostPosted: Dec Tue 31, 2019 3:16 am 
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Joined: Apr Sat 11, 2015 5:30 pm
Posts: 1149
Location: West Point, PA 19486
Use a clothespin to hold the wire!

http://analogdial.com/CoilJig/index.html


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