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charmanzer
Posted on Saturday, April 12, 2003 - 8:00 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

im wondering, say you have 2 one metre wires, with one of them you coil around a small pen, and with the other one you coil it around a large tube, would they have the same reception, or would one work better than the other?

i think this site is great!
im 13 from australia!
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Simon Quellen Field (Sfield)
Posted on Saturday, April 12, 2003 - 8:16 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

The two coils would have different inductances, and different capacitances.
They would resonate at different frequencies.

If you wound the two coils so they had the same inductance, and added capacitors
to make them resonate at the same frequency, the coil with the larger diameter
would have sharper tuning, and would thus be more selective.

Try playing with the Coil Calculator to see what different diameters will do.
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Deepak
Posted on Wednesday, September 24, 2003 - 5:56 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Any more places where u will get magnetic wires?
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mei
Posted on Monday, April 19, 2004 - 8:50 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

is it possible to encode a signal without using a computer?...that is to say, is it possible to talk into a radio transmitter--somehow encode that signal--and have my friend, across the street, be the only one who can hear--receive--a meaningful conversation? if so, how can that be achieved?
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nuinevu
Posted on Monday, April 19, 2004 - 9:07 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

the other day i went to a radio shack and asked for a Germanium diode(for the crystal radio), 2 workers said that either they didnt carry them or that Germanium diodes didnt exist...the third worker said to go to another retail store(very far away!)to see if they might carry that diode or to find out if it even existed
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Simon Quellen Field (Sfield)
Posted on Monday, April 19, 2004 - 10:35 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

These days a computer is probably the cheapest way to scramble
a signal, and probably the most secure method available to you.

Radio Shack used to carry Germanium diodes, but recently they
have cut back severely on their support of electronics hobbyists.
I think they still sell a crystal radio kit that includes a
Germanium diode and a piezoelectric earphone.

Because local stores often don't have the materials you need, we
have a catalog where you can order Germanium diodes and many other
things used in the book and on the web site.
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Lin
Posted on Sunday, June 6, 2004 - 1:06 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Hi! I working on the radio project that you have on your site and I just want to ask if I can use an ordinary earphone other than the piezoelectric earphone? are they the same? Is Cyrstal diode same as the Germanium diode becoz the workers stated that these two are the same? Thnx!!!
Scitoys.com is really a great and interesting site!!!!
By the way I'm from the Phlppnes.
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Andrew
Posted on Sunday, June 6, 2004 - 5:28 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

If by 'ordinary earphone' you mean the sort of headphones that might come with a CD player, then NO, they are not the same as a piezoelectric earphone. Im not sure about the diodes.
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Simon Quellen Field (Sfield)
Posted on Monday, June 7, 2004 - 12:32 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Both silicon and germanium diodes are made from crystals of their respective
substances. Germanium is more sensitive than silicon.

If you use an audio transformer, and connect the headphones to the 8 ohm
side and the radio to the 1,000 ohm side, then you can use ordinary headphones.
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Andrew
Posted on Monday, June 7, 2004 - 6:24 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Really? So a piezoelectric earphone works at 1,000 ohm?
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Simon Quellen Field (Sfield)
Posted on Monday, June 7, 2004 - 7:52 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

That's not how to frame the question.

The crystal radio can drive an impedance of 1,000 ohms or higher.
Lower impedances are harder to drive, and 8 ohms is way too low.

The piezoelectric earphone is between 100,000 and 1,000,000 ohms,
so it is very easy to drive, and will not load the radio very much
at all.
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Andrew
Posted on Wednesday, June 9, 2004 - 4:12 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

ok, that makes sense
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Anonymous
Posted on Tuesday, August 17, 2004 - 1:40 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

can I just use a npn transistor instead of the mk484
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Simon Quellen Field (Sfield)
Posted on Tuesday, August 17, 2004 - 1:52 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

No.
The MK484 is a 10 transistor integrated circuit that forms a complete
tuned radio frequency receiver.
You can make a simple radio using a single transistor, but the circuit
would be quite different, and the performance would not be as good.

If you do a Google search for "single transistor receiver" you will find
several, such as this one:
http://murray.newcastle.edu.au/users/staff/eemf/ELEC351/SProjects/Bastian/pg000006.htm.
or this one:
http://w1.859.telia.com/~u85920178/rx/regenrx.htm.
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Anonymous
Posted on Wednesday, August 18, 2004 - 1:32 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

how do you build a simple one transistor amplifer
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Matt Levine
Unregistered guest
Posted on Thursday, December 16, 2004 - 2:55 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I'm having trouble with your "Building a simple radio project". in the shopping list you say that i don't need to get insulated wire for the antenna because I can just attach the radio to one of the lead in wires on an FM radio. What do you mean Lead in wires? Also in the instructions, you say "attach the alligater jumper lead to the antenna". I think you should be a little more specific on how to make the antenna, and how the heck you are supposed to get an antenna on your roof or on a tree. Thanx for you help!

P.S. In the rotary high voltage motor, how many volts of electricity are required to make this project work. I did it on my TV and it worked, (it was really awesome!), is there any other way to do it besides using a computer, or TV?
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Matt Levine
Unregistered guest
Posted on Thursday, December 16, 2004 - 2:57 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Oh yeah, could you answer my last question by e-mail?
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Simon Quellen Field (sfield)
New member
Username: sfield

Post Number: 29
Registered: 12-2004
Posted on Thursday, December 16, 2004 - 3:42 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

If you already have a TV antenna on your roof (or
an FM radio antenna on the roof) then where will be
wires coming from the antenna and attaching to the
TV or radio. You can simply clip the alligator
clip to one of these wires, and you get a wire
going all the way up to the roof.

The antenna for the simple radios is just a long
wire. If it is uninsulated, you will need to
keep it away from the tree or house that supports
the ends, using insulators you can get at Radio
Shack or a hardware store.

The ARRL handbook, and the ARRL Antenna Book both
have lots more information on antennas.

As for the high voltage source, you can build a
Van De Graaff generator, a Wimshurst machine, or
you can use the guts of a "negative ion generator"
that you can get from All Electronics (or
Alltronics, I always get those two confused) for
about $8. It converts 9 to 12 volts into a few
thousand volts, and is pretty safe (you power it
with batteries).
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Matt Levine
Unregistered guest
Posted on Thursday, December 16, 2004 - 3:58 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

so, I can just have a wire hanging out of my window, and call it an antenna? Do I rap it around a stick or something? Is there anyway I can access The ARRL handbook, and the ARRL Antenna Book on the web? If not, where can I get these books?
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Simon Quellen Field (sfield)
New member
Username: sfield

Post Number: 30
Registered: 12-2004
Posted on Thursday, December 16, 2004 - 4:05 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Your library will have the books.
Or you can buy them.

Put as long a wire as you can as high as you can, and attach one end
to the radio.
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Matt Levine
Unregistered guest
Posted on Thursday, December 16, 2004 - 5:04 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

one more question. radioshack doesnt make germanium diodes ant more, so my dad got a silicon diode. He said there were several kinds, but he just picked one. Will any silicon diode work?
thanx
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Matt Levine
Unregistered guest
Posted on Thursday, December 16, 2004 - 5:05 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

in my last question i was referring to the simple radio project. I forgot to tell you that.
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Simon Quellen Field (sfield)
New member
Username: sfield

Post Number: 31
Registered: 12-2004
Posted on Thursday, December 16, 2004 - 5:30 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Germanium diodes work better.
That's why we carry them in our catalog.

A silicon diode will not pick up the fainter
stations that the more sensitive Germanium diode
will pick up.
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answerme!
Unregistered guest
Posted on Sunday, January 9, 2005 - 7:26 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

the laser communicator project: in the project,it says to use the two outer wires on the audio tranformer, but the laser pointer doesnt work, it only works if I connect it using either of the outer wires and the middle wire. I'm saying that the LASER POINTER only works when I use the middle wire, not the entire project. I haven't finished, I'm just not sure how to proceed. Thnx!
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answerme!
Unregistered guest
Posted on Sunday, January 9, 2005 - 7:36 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

oh yeah, and i got my tranformer from radio shack, not from the catalog.
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Simon Quellen Field (sfield)
New member
Username: sfield

Post Number: 103
Registered: 12-2004
Posted on Sunday, January 9, 2005 - 8:39 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

What was the Radio Shack part number?
It should be 273-1380.
They have many transformers, and only the one
labeled "audio transformer" has been tested.

If it is working for you the way you have it
configured, then go with it.

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