BFO as first detector

ham is all sorts of fun but I don't have the money to get any equipment for the moment.

I've been trying to debug the circuit without too much luck, at least I managed to create the audio connectors using the drawing tools the simulator comes with (circles, etc).

On a side note, I tried to make an etching solution out of Chloridric Acid and Hydrogen Peroxide (1-1, acid at 10% and peroxide at 3%) the solution worked, I tried it on a piece of copper tubing inside a test tube and it soon turned green, but as I stirred it today morning to add oxygen (it sat all night long) the test tube failed and the solution splattered throughout the room. I don't understand why this happened... I was using high grade pyrex tubes... Either way that was my lesson, I'll only do chemistry outdoors from now on.

It takes an accident to learn!

I'm still puzzled, pyrex should not fail like that. Even with a little piece of copper inside it shouldn't make a hole. For one the solution isn't that concentrated and secondly it takes a dremel tool to cut that glass...


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A whole liter of the acid is 5 bucks, in dollars that's ~$1.28 - The peroxide is even cheaper and you can find both elements in almost any place.

As for the ferric chloride, a quarter of liter is worth 10 bucks, which translates to $40 a liter, roughly $10.25 dollars. The thing is, you can hardly find it. (Remember I'm not in the US, we don't get to buy this sort of stuff around the corner)

Now both last for a very long period of time, but the latter is quite dark and it's harder to see the PCB without taking it out the tray, the former is green and you can see through it even on a half liter concentration.

I have ferric chloride, don't get me wrong. But I would really like to try the other etching solution because it's supposed to be faster. Equally dangerous, perhaps. They are both a hazard to nature anyway and I wouldn't even dare to dispose such a solution on the ground.




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How is using a sponge and getting rid of the copper that is not underneath the resist any bad?, the way I see it if you use a bath and you're not careful with the time / temp you'll end up with pitting, etc. If you can use a sponge and get rid of the copper almost in real time you can prevent this by putting the board on water immediately once you've reached your etching goal. We're talking about small boards here.

Spraying works on a similar way but requires a rather complicated setup to be precise during the etching process.



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adnimo;

The test tube:-  was it stoppered, if so, it may have built up pressure (hydrogen gas, from the reaction,) and fractured from that pressure.

The old fashioned quartz glass (like Roman glass) was worse, very brittle and tended to break easily, but heat proof. The best are borosilicate, tough and relatively shatter-proof.

I have been playing with pc board software and simulation software, but it is all crazy. For instance, checking the circuit integrity says all the leads, to the outside , power, input, output, etc, are "open." But of course they are, even when tagged! I am giving it a few days rest and going to a breadboard. 

goldigger



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		Quote:			Posted by BAATAR
	any one describe BFO detector?

Bataar;

Nice of you to ask.

Basic BFO: you have two oscillators, operating at nearly the same frequency; one is the search oscillator (the search coil) the other is called the REFERENCE oscillator. They have to be isolated so they do not interlock.

BFO search oscillators need a shield, called a Faraday shield, to reduce capacity effects, like when the coil passes near a plant like grass or a small bush, without a Faraday shield it will give a false indication,

To tune:-  the reference oscillator is tuned until you hear a tone, a low tone is best, or you can get ear fatigue (really,) so when the search coil goes near metal, like a coin or piece of gold or an old iron covered battery, for instance, the tone changes. That tone change is how you know there is metal present.

If the reference oscillator is tuned just below the search oscillator, iron will make the tone go down. Aluminum, gold, copper, any non-iron, non-ferrous metal will make the tone go up. Do you want a technical explanation? 

BFO locators are only as sensitive as your ear, I have made BFO locators that used a harmonic of the search frequency and got more sensitivity.... more instability, also.

There is a trade-off in the frequency used, and that is: 100 kHertz is more sensitive to small objects, but does not penetrate the ground well, because of "ground effect," Then again 10 kHertz penetrates the ground well but is not as sensitive to small things.

This would indicate 45 kHz should be a happy medium. It is halfway from 10 kHz to 100 kHz.

A phase sensing circuit works on the same principle as a BFO but the frequency change is less than 90 degrees.... you would never hear that small a change but it can be detected, electronically.

Hope this helps.

goldigger

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