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Jason
Posted on Friday, May 30, 2003 - 4:20 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

What I am trying to achieve is a physics project in which i'm supposed to send a message from one room to another. So far i'm only sending a signal from my CD player to my AM radio. The signal only travels a couple feet and is extremely quiet. I did what you said, I used a good ground (the cold water pipe in my kitchen sink) and my antenna is about a yard. What can I do to improve the range to about 20 feet? Once I accomplish a suitable distance, I'm hoping to use an eight inch speaker (it was just lying around, the only thing i had) as the microphone. The problem is that the signal is too weak to transmit. What size amp do you think would be sufficient, or should I use something else for the microphone? I'm in a sort of rush to get it finished, so a quick reply would be greatly apprecated. Thanks for the help, your site is great.
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Simon Quellen Field (Sfield)
Posted on Friday, May 30, 2003 - 12:52 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

The Computer Controlled Transmitter project might be
better for this purpose, since Morse code will go much
farther than speech, because of the low bandwidth, and
the 100% modulation.

A larger antenna will help. Try a hundred feet of
wire looped around the room. A good receiver will also
help.

A one-transistor RF amplifier can be built for the device,
but that would probably make it illegally powerful. The
amplifier is much more difficult to build than the transmitter
however, and you may not have enough time to learn about
transistor electronics and RF output filters. A good source
is the ARRL handbook.

You might also try increasing the modulation percentage by
putting more power into the audio going into the transformer.

An normal stereo will probably work fine as the amplifier,
although you might want a real microphone -- they aren't
very expensive.
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Anonymous
Posted on Thursday, June 5, 2003 - 8:56 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Can you tell me where to take a oscillator 1Mhz? I live in Viet Nam and it's not easy to buy one. Can you tell me what things that i can find a oscillator inside?
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Simon Quellen Field (Sfield)
Posted on Thursday, June 5, 2003 - 1:59 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Because our readers around the world sometimes find parts
difficult to obtain, we stock those parts in our catalog,
to make it easy. We ship all over the world.

See this page for the oscillators.
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Anonymous
Posted on Friday, June 6, 2003 - 1:01 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I see but I don't have a credit card, i think i have to make one.
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Simon Quellen Field (Sfield)
Posted on Friday, June 6, 2003 - 6:36 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Making a credit card is beyond the scope of my web site.
But I am certain you can get help elsewhere on the Internet.

Of course you could always pay someone with a credit card to
make the purchase for you.
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Anonymous
Posted on Saturday, June 7, 2003 - 4:27 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Thanks!
One more question: why don't you add more toy in your site? Your site is great!
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Simon Quellen Field (Sfield)
Posted on Saturday, June 7, 2003 - 2:26 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I am continually adding new material to the site.
But it takes time to design and test the projects,
and more time to write instructions that people can follow,
and to explain how they work to a broad audience.

Have patience ;-)
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Fred Callahan
Posted on Thursday, September 4, 2003 - 5:18 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Simon, I don't think our friend in Viet Nam meant he wanted to make a credit card, I think he wants to make an oscillator.
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Simon Quellen Field (Sfield)
Posted on Thursday, September 4, 2003 - 11:31 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Sometimes irony is inescapable.
And then sometimes it escapes people.

Oh well.
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Anonymous
Posted on Monday, April 19, 2004 - 8:04 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

how can one build an oscillator?
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Simon Quellen Field (Sfield)
Posted on Monday, April 19, 2004 - 8:15 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

When you hold a microphone too close to the speaker,
you hear a squeal of feedback. That is an oscillator.

What you need to make an oscillator is an amplifier,
with some or all of its output fed back to its input.

The frequency of oscillation is controlled by the delay
in the feedback. In the microphone and speaker, the delay
is caused by the time it takes sound to get from the speaker
to the microphone. This is why the sound changes pitch as
you move the microphone closer to the speaker, or farther away.

In oscillators at radio frequencies, the delay is often caused by the
time it takes to charge a capacitor. An amplifier has its input and
output connected by a capacitor or a quartz crystal, which provides
the delay.

You can use Google to search for "oscillator circuit" to find many
different types of oscillators that you can build.
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mei
Posted on Friday, May 7, 2004 - 2:50 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

do you accept money orders, or cash as substitutes for credit cards?
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Simon Quellen Field (Sfield)
Posted on Friday, May 7, 2004 - 5:21 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

At this point we only accept Visa, MasterCard, and American Express.
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Alex L
Unregistered guest
Posted on Monday, July 11, 2005 - 9:35 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I did the same exact thing as jason, a yard of antenna, and a good ground, playing music with my cd player. I only have 1 radio that will pick up the signal and I have to turn the volume all the way up on both of them in order to hear it. The signal also only travels a couple feet. On my transformer the red and white wires were reversed from yours, but I still used them the same way. Same with the blue and green audio wires, but I still followed the directions the same. Is this the problem? Am I wording this right, I still used the same colors in the same places.
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mnado (Mnado)
Senior Member
Username: Mnado

Post Number: 128
Registered: 12-2005
Posted on Sunday, January 29, 2006 - 2:49 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

simon what does oscillators do?what special instrument does it have inside that it can send waves?i tried google but this time its use less,the only destination it goes it where to buy one,can you just explain it to us how oscillators work?
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Angus Chalmers (Fungus)
Intermediate Member
Username: Fungus

Post Number: 46
Registered: 12-2005
Posted on Sunday, February 12, 2006 - 8:46 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Oscillators change DC into AC. They are rated at the frequency at which they oscillate: i.e the 1 mhz oscillates 1 million times per second. They are basically a feedback loop where the output changes the input.

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