What am I doing wrong with this radio? Science Toys | Science Blog | Log Out | Topics | Search
My Toys | Energy | Moderators | Register | Edit Profile

Scitoys Message Board » I am having trouble building one of the toys » What am I doing wrong with this radio? « Previous Next »

Author Message
Top of pagePrevious messageNext messageBottom of page Link to this message

Cody (Codym)
New member
Username: Codym

Post Number: 1
Registered: 12-2006
Posted on Friday, December 22, 2006 - 10:42 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

So I've been looking at a few more complicated schematics for basic AM recievers, and I've tried to build a couple, always resulting in failure, so I decided to do something extremely basic, without even a tuner, just hoping to pick up some static, and it has still resulted in failure. I hear the initial feedback when plugging in the headphones, then complete silence. Could anyone fill me in on what I did wrong? By the way I'm really new to this kind of stuff, so thanks for the patience =D
Below is my schematic.
Schematic
Top of pagePrevious messageNext messageBottom of page Link to this message

I. Dimov (Overrider)
Senior Member
Username: Overrider

Post Number: 118
Registered: 12-2005
Posted on Saturday, December 23, 2006 - 5:59 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

The impedance of the headphones is too low, or the ninevolt battery is jamming the signal, also it could be the diode. It must be germanium.
Top of pagePrevious messageNext messageBottom of page Link to this message

Cody (Codym)
New member
Username: Codym

Post Number: 3
Registered: 12-2006
Posted on Saturday, December 23, 2006 - 6:06 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

If it is the 9v battery jamming the signal, what can I do to stop that, use less battery power?

And I'm not using a germanium diode, but what makes a rectifier diode not usable for this situation?

Oh, and I also just discovered that my headphones have a 32 ohm impedance. How can I tell if that is too low or high?

Thank you for the help, I'm very new to this :-)
Cody M.

(Message edited by codym on December 23, 2006)
Top of pagePrevious messageNext messageBottom of page Link to this message

Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1605
Registered: 12-2004
Posted on Saturday, December 23, 2006 - 8:57 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

The battery is doing nothing in this circuit.
Likewise for the rest of the parts, since they are not put
together in any meaningful manner.

Read the entire radio chapter. It is not that long, it will probably
take you less than an hour:
"http://sci-toys.com/scitoys/scitoys/radio/radio.html".

Just throwing parts together and hoping will not do it, you have to have
some basic theory.

32 ohms is too low for a crystal radio, and you have no amplifier, so you
are trying to build a crystal radio, although you have added a battery,
despite having no parts that can use one. You want an impedance between
1,000 to 1,000,000 ohms.

You can convert your headphones to an impedance that will work by using
an audio transformer:
"http://www.scitoyscatalog.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=XFORMR&Category_Code=R".

Throw away your circuit, and use the one on this page:
"http://sci-toys.com/scitoys/scitoys/radio/ten_minute_radio.html".

Connect the 1,000 ohm side of the transformer where the piezoelectric
earphone is in that schematic. You won't need the middle leg of the
transformer -- leave it unconnected.

Connect the 8 ohm side of the transformer to your headphones.

You can get all the parts for the radio here:
"http://www.scitoyscatalog.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=SIMPLE&Category_Code=R"

It is guaranteed to work.
Top of pagePrevious messageNext messageBottom of page Link to this message

Cody (Codym)
Junior Member
Username: Codym

Post Number: 4
Registered: 12-2006
Posted on Sunday, December 24, 2006 - 2:06 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Thank you very much for the input. The site is an awesome referrence, and has motivated me greatly to do projects like this, and you, Simon, are a very knowledgeable and helpful individual, and I appreciate how willing you are to teach those in need. I also appreciate the people in the forum for being so helpful.

I am looking forward to putting this together, but since it's the holiday season, all the electronic stores in my area are closed for the next few days. As soon as they open back up, I'll get what I need and tell you how it goes!
Thank you!
Cody M.

Add Your Message Here
Post:
Username: Posting Information:
This is a private posting area. Only registered users and moderators may post messages here.
Password:
Options: Enable HTML code in message
Automatically activate URLs in message
Action:
For those who have trouble spelling, the Google Toolbar (included in the Google Pack) can check and correct the spelling in your posts on this message board and others.

Renewable Energy

Topics | Last Day | Last Week | Tree View | Search | Help/Instructions | Program Credits Administration