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**trash** · 22-07-08, 02:58 PM

Yes Z80, you might have also discovered that you can use just about any two dissimilar conductors to produce a slight rectifying effect.
My favourite material is graphite, (pencil lead) on any metal, especially razor blades.
Galena as a minerial is always fun to use. Lead is in the same group as Carbon, Silicon, Germanium and Tin all of which are used for their rectifying properties as well as some of the elements in the neighbouring groups.
Want a good crystal radio project ... make your own diode by growing tin whiskers on a substrate.

I've been meaning to make an FM crystal radio using a cavity and a germanium ratio detector. I'll get around to it one day.

My last weird arse project was to make a glass of water transmit are radio signal !
I can hear the crowd shout "BULLSHIT" ! So I'll describe the process.

The first task is to make the water a semiconductor.
A salt makes the water conductive, a metal probe provides the dissimilar conductor.
That part is simple, you already have the basis for a glass of water crystal radio. (yes it does work Z80).
The trick to making a diode transmit is that you need it to have a negative resistance. An example of a real diode that does this is a Tunnel Diode.
Tunnel diodes were used in all kinds of oscillators, a variation of the tunnel diode is a Gunn Diode, used in microwave modules and police radar etc.

So how do you make a glass of water have a negative resistance ?
Choose the type of salt and the metal probe carefully.
Borax and Aluminium are a winning combination.
Aluminium is very easy to come by, borax used to be found at chemists* but because everybody is a terrorist, you'll have to buy it at the local garden shop.
The Aluminium needs to have the smallest point contact possible. I use aluminium cans split to form an aluminium splinter and the point just touching the surface of the water.

You can test the negative resistance of your glass of water with a voltage divider and a milliammeter. The ammeter will drop as your raise the voltage across the diode, this is the negative resistance region and the voltage that you need to run your diode at. If you have a spectrum analyser (I do) you will notice RF noise coming from the glass of water !

So now it's just a matter of cleaning up all that RF power.
A tank circuit does it nicely ! I wind a coil around the glass using it as the former. A bit of clever engineering I have a metal plate (aluminium foil) on the top and bottom of the glass to make a capacitor.

Apply the power and VOLA ! A carrier appears.
That's how you make a glass of water transmit !

I find that most of my carriers end up in the HF section of the band anywhere from about 5 to 20MHz depending on coil windings.

Just in case you're thinking that DXCC on a glass of water is going to be possible, the best output power I've managed to achieve has been about -20dBm, or 10uW which is a very tiny signal.

But even with this tiny amount of power, you can use a shortwave radio and hear the carrier up to 100m away.

===

The Chemist.
I wondered into my local chemist and asked for some borax. I've bought plenty of borax from chemists in the past 25 years and never had a problem.
The assistant approached the dias upon which the chemist was perched.
He looked down upon me and decended from his lofty postion to interigate me.
Why do you want borax ?

Shit ! How do I explain this ? Ok, he's a smart guy, he might understand.
"I'm making a negative resistance semiconductor using a glass of water !"
Do you know the Doc from "Back to the Future" ? Yeah, well that's the look I got from the chemist who immediately decided that a 'negative whatever' was some sort explosive.
I don't know what it is your trying to do but it sounds as bad as asking for Iodine.

At this point, my view of the chemist as being the smarter person changed.
I pointed to the tincture of iodine the nearby shelf and to a cleaner which I knew would have 'ammonium hydroxide' and told the chemist that if I was going to ask for material to make explosives, I would not ask him directly for those materials and instead would purchase the tincture of iodine and refine it without his knowledge.
It was about then he suggested I leave.

BigW next door had Borax in the garden shop.
I wonder if he called the terrorist hotline ?

22-07-08, 02:58 PM	#29 (permalink)
trash Senior Member iTrader: (0) Join Date: Jan 2008 Posts: 344 Spent time on board: 2 Days and 18:50:56	Yes Z80, you might have also discovered that you can use just about any two dissimilar conductors to produce a slight rectifying effect. My favourite material is graphite, (pencil lead) on any metal, especially razor blades. Galena as a minerial is always fun to use. Lead is in the same group as Carbon, Silicon, Germanium and Tin all of which are used for their rectifying properties as well as some of the elements in the neighbouring groups. Want a good crystal radio project ... make your own diode by growing tin whiskers on a substrate. I've been meaning to make an FM crystal radio using a cavity and a germanium ratio detector. I'll get around to it one day. My last weird arse project was to make a glass of water transmit are radio signal ! I can hear the crowd shout "BULLSHIT" ! So I'll describe the process. The first task is to make the water a semiconductor. A salt makes the water conductive, a metal probe provides the dissimilar conductor. That part is simple, you already have the basis for a glass of water crystal radio. (yes it does work Z80). The trick to making a diode transmit is that you need it to have a negative resistance. An example of a real diode that does this is a Tunnel Diode. Tunnel diodes were used in all kinds of oscillators, a variation of the tunnel diode is a Gunn Diode, used in microwave modules and police radar etc. So how do you make a glass of water have a negative resistance ? Choose the type of salt and the metal probe carefully. Borax and Aluminium are a winning combination. Aluminium is very easy to come by, borax used to be found at chemists* but because everybody is a terrorist, you'll have to buy it at the local garden shop. The Aluminium needs to have the smallest point contact possible. I use aluminium cans split to form an aluminium splinter and the point just touching the surface of the water. You can test the negative resistance of your glass of water with a voltage divider and a milliammeter. The ammeter will drop as your raise the voltage across the diode, this is the negative resistance region and the voltage that you need to run your diode at. If you have a spectrum analyser (I do) you will notice RF noise coming from the glass of water ! So now it's just a matter of cleaning up all that RF power. A tank circuit does it nicely ! I wind a coil around the glass using it as the former. A bit of clever engineering I have a metal plate (aluminium foil) on the top and bottom of the glass to make a capacitor. Apply the power and VOLA ! A carrier appears. That's how you make a glass of water transmit ! I find that most of my carriers end up in the HF section of the band anywhere from about 5 to 20MHz depending on coil windings. Just in case you're thinking that DXCC on a glass of water is going to be possible, the best output power I've managed to achieve has been about -20dBm, or 10uW which is a very tiny signal. But even with this tiny amount of power, you can use a shortwave radio and hear the carrier up to 100m away. === The Chemist. I wondered into my local chemist and asked for some borax. I've bought plenty of borax from chemists in the past 25 years and never had a problem. The assistant approached the dias upon which the chemist was perched. He looked down upon me and decended from his lofty postion to interigate me. Why do you want borax ? Shit ! How do I explain this ? Ok, he's a smart guy, he might understand. "I'm making a negative resistance semiconductor using a glass of water !" Do you know the Doc from "Back to the Future" ? Yeah, well that's the look I got from the chemist who immediately decided that a 'negative whatever' was some sort explosive. I don't know what it is your trying to do but it sounds as bad as asking for Iodine. At this point, my view of the chemist as being the smarter person changed. I pointed to the tincture of iodine the nearby shelf and to a cleaner which I knew would have 'ammonium hydroxide' and told the chemist that if I was going to ask for material to make explosives, I would not ask him directly for those materials and instead would purchase the tincture of iodine and refine it without his knowledge. It was about then he suggested I leave. BigW next door had Borax in the garden shop. I wonder if he called the terrorist hotline ?