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Offline DeewayneTopic starter
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« on: November 06, 2010, 03:53:34 pm »
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I am so new to MD'ing my MD is still somewhere in the UPS system.

I have ordered a BH QDII, Which I believe is an VLF type detector.

I don't even know if what I am thinking of can/will work (that's why I'm on this forum.)

What I have in mind is installing a switch box in the cable between the electronics and the search coil. This switch will be used to switch between the standard 8" coil and a new pinpoint detector coil (stick type.)

Can I make just the pickup coil? If so how should it be constructed?

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Offline GoldDigger1950
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« Reply #1 on: November 07, 2010, 02:20:07 am »
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I split your question from the original thread into a new one that is specific to your needs.

Yes, it can be done but you do need to be aware that the coil has to be a two part coil. A transmitter and receiver coil are required to work with your machine. Making a pinpointing probe that small can be a nightmare of impedance matching issues to keep your entire detector tuned properly. If your machine is under warranty, it may not be worth it.

The switch needs to be a sliding contact rotary switch that never opens completely. It must switch between the two coils without leaving an open circuit for even an instant or the detector will make the most dreadful noise for that instant and could even blow out your speaker or headphone. Look for a switch that has "make before break" characteristics. An open circuit in a tuned circuit should never happen.

Next, the coil should be one that matches the original coil's inductance, capacitance and resistance characteristics as closely as possible. This is where the nightmare comes in. Most people use a ferrite core AM radio antenna, which has two sections. Use the smaller section as the TX coil and the larger one as the RX coil. This doesn't sound very technical but the truth is, it often works quit well.

I prefer a separate pinpointer. I have an arsenal of detectors and I can use it with all of them.

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« Last Edit: November 08, 2010, 02:29:45 pm by GoldDigger1950 »
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« Reply #2 on: November 07, 2010, 09:27:56 am »
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Have to agree with GD...
On a P.I. detector this is easy to do (you only have the one coil to worry about).
A seperate pinpointer is really the best option.
Have you considered making one?
You could always "kill 2 birds with 1 stone" so to speak.
Silverdog is selling a kit (surf p.i.) whick would make a superb pinpointer AND a great P.I. detector for the beach!


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Offline Mudflap
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« Reply #3 on: November 07, 2010, 10:45:19 am »
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Welcome. I prefer a seperate pin pointer. The isssues as Golddigger mentioned. Also if the impedence of the switch and its connections change you can have ground balencing issues. The switch would have to be a good quality. I like Paul's suggestion. Build a seperate small PI pinpointer.
Jim

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