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Offline hargrovebrianTopic starter
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« on: February 12, 2010, 12:13:58 pm »
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Hello

I have purchased a P I detector. can I make a 8 ft coax coil for it.

Thanks Brian

How about an bfo detector?

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Offline yourownfree
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« Reply #1 on: February 17, 2010, 12:32:10 am »
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I see 53 views and no reply's, So I will post my thoughts on it.  There is no reason why you cant do that. As a matter of fact, when I make my own, I use coax. That way it keeps the stray crud from entering other than the coil. The PI should have one coil anyway unless it has a canceling coil. Same as for bfo. bfo has one coil in the head and the other coil is in the box. In most cases anyway. I have seen the the two coil in the head.I am assuming the length of the original coax is not long enough for you, so you are trying to make a longer one? Its ok. Make sure you get the shield and center connected properly. Make sure you note which one goes to the center and the outside from your search head coil and at the box. bfo type have a Faraday shield that needs to be hooked to ground potential. Would not work right if you got that mixed up, (reversed) with the center wire. In some cases a two wire or more shielded cable might be what you need. What does your detector have now? coax with center and outside, or a multi-wire shielded cable? Use the same style, and more length will not hurt anything.

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« Reply #2 on: February 18, 2010, 01:06:13 pm »
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The reason he has thus far received no replies is because his question is unclear. In the subject, he implies he is asking about coax cable. In the body, he seems to be asking about a coaxial coil. Personally, I figured he was a bit confused since, as you note, there would not normally even be a second coil to be coaxial. Regarding coil wires, almost all of them that I have seen have been shielded multiwire cables, often incorrectly referred to as coaxial. Since a true coaxial cable is only two wires, that muddles the request even further.

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Offline hargrovebrianTopic starter
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« Reply #3 on: February 21, 2010, 11:59:32 am »
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Hi

 I want to make a search coil for a pi detector from a (TV) coax cable

Is this possable thanks for the differense in cables
Brian

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Offline GoldDigger1950
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« Reply #4 on: February 22, 2010, 03:23:41 pm »
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Quote:Posted by hargrovebrian
Hi

 I want to make a search coil for a pi detector from a (TV) coax cable

Is this possable thanks for the differense in cables
Brian


If you use the shield wire, yes, but not the signal wire because the shield will keep it from transmitting. Then, if you use the shield wire, there's not much point in trying to impedance match it to anything because the braided wire make it impossible to measure or determine the reactivity.

Use enameled copper wire. Best choice and cheap.

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« Reply #5 on: February 22, 2010, 07:40:34 pm »
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I'm still confused.

Is he talking about the lead in wire or the coil it's self?

Eight foot of RG - 6 would have a bit on the high side of capacitance and drag out the response time.

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« Reply #6 on: February 23, 2010, 06:11:01 am »
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Hi

both the lead in wire, the 3 way spliter, and the 16 ft coil  coax cable.

Brian

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« Reply #7 on: February 23, 2010, 08:22:01 am »
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I would think the shielding in the cable would block any target signal.

Most splitters for TV,Cable use are resistive networks and would be toasted!   Funny

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« Reply #8 on: February 23, 2010, 03:56:32 pm »
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Quote:Posted by hargrovebrian
Hi

both the lead in wire, the 3 way spliter, and the 16 ft coil  coax cable.

Brian


Won't work.

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« Reply #9 on: February 24, 2010, 01:41:51 am »
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After looking over some literature I am correcting my statement earlier as I jumped the gun. It appears because you are using a PI machine that the length of the coax does make a difference and what type you use. The coax will add capacitance to your coil circuit which will result in a slower coil and even to the point of not detecting as well. I cant say how much a difference it will make. Certainly will have to readjust settings as they will most likely be different. Check your coax cable specs to see how much capacitance it adds per foot against other types. Some might be around 15pf where others might be around 30pf. Smaller is better in this case. The best is to have the shortest possible cable to the have the fastest coil, microseconds wise that is. The less the capacitance the faster.

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