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Offline Homefire
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« Reply #30 on: September 02, 2010, 11:12:54 am »
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How and why would you retard the TX Signal?

All you want to do is compare the two.

You just need a Arbitrary Point and take samples from there?

Is the Current Ahead of Voltage or Lagging?

It's all a funtion of 2Pfl.

I'm Confused.

Capacitance Lags current by 90 degree and Inductance ( Voltage) leeds by 90 degree.

I would think the right set up of Compartor would do the job?



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Offline xavier
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« Reply #31 on: September 02, 2010, 03:12:42 pm »
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You think you're confused you should see my face!   I see what you are saying now with the comparator OK well back to the books will keep you posted.

Regards Xavier

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So many questions so little time

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« Reply #32 on: September 02, 2010, 03:27:51 pm »
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I know electronics but wizz I are Not.

Could you use the output from a PLL Phase Locked Loop? It could be based on the TX freq?

You could use the Correction Voltage Based the Return or Received signal to determine the phase change?

You could bias the correction voltage and use it as a type of  Ground Ballance?

Just the Ramblings of a sick Mind.

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Offline GoldDigger1950
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« Reply #33 on: September 02, 2010, 04:24:39 pm »
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The return signal on metal in the ground is so weak that the TX field can mask it. You have two choices. Either you can do a RX reading while the oscillating TX signal is doing a zero crossing (that's when the voltage is at zero as it oscillates from positive to negative) or you can turn off the TX pulse for a short time. The latter is what is done most easily in homebrew designs. Doing an RX reading during this quiet time is the best way to sense the collapsing fields on the metal in the ground. That collapse starts just as soon as the TX goes silent and lasts until all of the energy in the metal is gone. It's not long. The timing between turning off the TX and starting the RX is critical. Do it too soon and the TX field will not have collapsed yet causing the RX to see a target which isn't there.

This, by the way, is the most common cause of the question, "My DIY detector makes a solid beep. What did I do wrong?"

If you turn it off too late, as may be the case with Xavier, the signal is sensed at a greatly diminished distance because the field resulting from eddy currents in the target has already diminished to a lower than optimum point. The Fo, commonly called the "F sub O," or frequency of operation has an effect on this collapse time based on three factors. The type of metal, mass of the metal and the shape. All three have different effects on the field that is there and those differences are how discrimination works. Thus, some frequencies are better for finding gold nuggets, some better for finding gold coins and some better for finding gold rings. Because shape and mass play a part, that explains why you can find a small gold ring and sometimes miss a big one. You can experiment with this if you are lucky enough to have a gold coin, nugget and various sized gold rings in your collection. Keeping a chart of each of your detectors and their response can improve your odds in the field.

Homefire, you already know about the relationship to timing in PI circuits. You once recommended a resistor change to me for my Sea Hunter which would have changed to timing relationship to one better suited to gold targets.

Xavier, a square wave is an infinite number of sine waves being switched on and off. It will have zero difference electronically.

Isn't this dry, boring theoretical stuff fun? As we continue to discuss these things, you can get a glimmering of why it is so difficult to see a newbie trying to build a metal detector from parts. It's a bit like watching a farmer try to build a tractor from iron ore. We all know it can be done but the question is, "Should the farmer really do it himself?"

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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
Let's Talk Treasure!

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« Reply #34 on: September 03, 2010, 01:34:31 am »
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Hi GD

Well this one is printed too I was thinking like you mentioned in your first paragraph to switch off the TX then Homefire mentioned using a comparator and I think that I will go that rout I do not have the experience or knowledge yet to go any other way. I was thinking to use the received signal to switch of the TX but that may be too late so what I think I should do is make a signal generator and a receiver hook it all up to the PC scope then see what I can come up with.

Regards Xavier   

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So many questions so little time

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« Reply #35 on: September 23, 2010, 05:46:25 am »
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I want it now! But I can't download the files yet! I don't have 5 posts!

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« Reply #36 on: September 23, 2010, 09:43:05 am »
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LOL! you just made Number 6!

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« Reply #37 on: September 23, 2010, 11:07:28 am »
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Ho I do wonder at times  Grin

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So many questions so little time

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« Reply #38 on: November 09, 2010, 09:19:51 am »
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i haven't been here in awhile. has someone figured this thing out?

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« Reply #39 on: November 09, 2010, 10:51:18 am »
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LOL!  You have just been bumped to Guru Status!   

Were waiting for you post.



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