Should search coil be tuned to your detector??

[R-bass]

I like to know with all these after market coils out there do they out perform the manufacture coils that are designed and tuned for there metal detectors.
Plus if you had a choice what kind of metal wire would you use inside a coil . Call me crazy but would gold wire be a good choice if the cost wasn't so high

 

[d1g1man]

"I like to know with all these after market coils out there do they out perform the manufacture coils that are designed and tuned for there metal detectors.
"
Some do,some don't. Many are advertised as such. It also depends on what you call "out perform" some people will take a coil that weighs a ton compared to a coil that weighs an ounce, just for an inch more depth, and this, they would call "out perform". Best bet is read every review you can possibly find on the coils you are considering, make sure you get the one that matches the environment that you are wanting to detect, and is the proper size and type for your desired targets. An example of this would be, you would not want an 18" coil to go looking jewelry in a trashy park, nor would you want to use a 6" coil for searching for a 4 foot deep cache.

"Plus if you had a choice what kind of metal wire would you use inside a coil . Call me crazy but would gold wire be a good choice if the cost wasn't so high"

From the coil to the box and back again is one big tuned circuit the coil would have to be tuned or resonant on the frequency that the detector uses. Gold is currently the best known conductor, and yes if you made a coil out of gold it would have some superior properties, but not enough to use it even if it was cheap. Copper is cheap enough, and has the right tensile and strength qualities necessary for coil construction. The average coil contains 22-24 AWG enameled copper wire in it. Much like that you would see in a motor winding. Aluminum could also be used in place of gold or copper, being light and having slightly better conductivity and less resistance than copper. However aluminum does have some negative qualities. This is why they stopped using it in residential wiring systems (in the US anyway).

Here is some basic topographic information on the subject.
http://en.wikipedia.org/wiki/Electromagnetic_coil

I hope this info helps. -digi

 

[Carl-NC]

My experience is that aftermarket coils sometimes are not nulled as well as a stock coil, which can be a problem in hot ground. Any additional depth you might get out of an aftermarket coil is usually the result of it being a larger size than the stock coil. That is, aftermarket coil makers don't have any "magic techniques" that detector makers don't know about.

"...the coil would have to be tuned or resonant on the frequency that the detector uses."

Usually not.

"Gold is currently the best known conductor..."

Definitely not. Copper is better than gold, and silver better than copper.

"Aluminum could also be used in place of gold or copper, being light and having slightly better conductivity and less resistance than copper."

Aluminum is worse than copper.

If I were winding coils, I would use copper.

- Carl

 

[;hgarr]

Hi R-Bass...Regardless of the detector or the loop, the specific loop is usually tuned to the specific model detector. The tuning in some loops is critical to deep and quiet operation....Your question on the type of wire used in the loops can be a can of worms. The wiring gage and composition used depends on many factors, especially those of end usage. Wiring varies varies all over the place, including Silver (highest of all conductorts----lowest resistance to electric current----, but much too soft for many winding configurations, but is used in some cases where large gage sizes is needed to get a proper "Q" in a winding). Copper is the most used material becdause of mechanical properties that engineer well in loop windings, and it is the second highest conductor available. Large Aluminum windings (alumiunum is a medium conductor metal) were used years ago in in certain loop windings in order to achieve high inductance with minimum weitght in the loop, but has mostly been preceeded with Litz wite configurations in order to minimize capacitance and other problems with large gage sixes or large inductance ranges of low frequency loops used today, or high performance PI loops. Gold is a low conductor metal, is extremely softt, is hard to work with and is not recommended for use in metal detector windings. Gold is mostly used in electronics as a protective plating on connectors and PC Boards (Military and space).....I hope this is not too confusing. Winding successful coils is an engineering art and some designs are more successful than others, and lately are getting really deep and separating targets really well...... Good luck in your metal detecting adventures....How.

 

[d1g1man]

Sorry, had to refresh my memory. Gold is third.

Silver: best

Copper: 9% less conductive than silver

Gold: 24% less conductive than copper (but doesn't tarnish or corrode)

Brass is somewhere here.

Rhodium: 74% less conductive than copper

Iridium: 77% less conductive than copper

Platinum: 84% less conductive than copper

Titanium: Over 99% less conductive than copper

 

[Steve(MS)]

Carl, what metal do most manufacturers use when building coils?

 

[d1g1man]

"...the coil would have to be tuned or resonant on the frequency that the detector uses."

"Usually not."

OK, I am thinking in terms of RF. I know that the frequencies we are dealing here are AF right? (and not capable of RF propagation)

If the coil is actually resonant, like say a full wave resonant loop. At 15 kHz, which is .015 MHz (length = 1005/MHz) the coil would be like 31200 feet long.
That might be kind of heavy.

So does the circuit have to be resonant like an RLC network?
This makes me wonder why we cannot make, say a 6.59kHz coil work on a 15kHz detector? It seems like it would reduce the efficiency though.

"If I were winding coils, I would use copper."
You do wind coils right? I could swear I read somewhere you did. What gauge would you recommend for experimentation?

The reason I ask is I am learning as much as I can, it might be possible to wind a snooper 350 for the DFX. Why there is not one like this by White's or Excelerator I do not know.

Sorry to ask, kind of off topic. But there is an engineer in the room and I can't pass up the chance to learn something, forgive me!

 

[thebeatmachine]

The concentric coils are wound and then tuned with capacitors that are at in the search head housing. I don't know if both loops are tuned with caps but the Tx definitally is. You can hook a frequency counter to the tx coil wires of the Classics and sure enough it reads 6.5x khz I don't know why this fascinates me so much.

How is the new project going at White's Carl? I f you can post us a video of yourself demonstrating it while telling us about some of its features it would be greatly preciated, Just wait until Mr. White is out on lunch break or something..

 

[Elton]

When a detector is made it has a designated frequency or frequencies out put, and pull back. The coils are tuned to those frequencies. BUT, there is a plus and minus factor when the factory does the settig up. A certain tolerance is allowable -10 to +10 on some specs. So it goes without saying sometimes you get a coil thats speced perfect for the machine. Sometimes you don't..Hence some detectors of same brand and model are deeper, or more stable than others run the same day or week, or month..

 

[R-bass]

With the kind of money we spend on metal detectors these days i hope that the manufactures are keeping a very high standard when it comes to material and quality control.
But if a coil that uses silver wire instead of copper wire how much more would the silver coil gain if silver is better than copper in conductivity. How much depth and sensitivity
if you use silver wire in a coil. I know that silver coins give a good sound from other detectorist that find have found them. So two quarter one silver and one not can some one
do a test on depth and sesitivity i would do the test myself but don't have a silver quarter. any comments thanks R-bass.....

 

[Steve(MS)]

I think I read somewhere that coilmakers use aluminum wire in their coils, now I don't know that for sure.
Maybe someone with the knowledge of this can share.

 

[Carl-NC]

"...the coil would have to be tuned or resonant on the frequency that the detector uses."

"Usually not."

OK, I am thinking in terms of RF. I know that the frequencies we are dealing here are AF right? (and not capable of RF propagation)

If the coil is actually resonant, like say a full wave resonant loop. At 15 kHz, which is .015 MHz (length = 1005/MHz) the coil would be like 31200 feet long.
That might be kind of heavy.

So does the circuit have to be resonant like an RLC network?
This makes me wonder why we cannot make, say a 6.59kHz coil work on a 15kHz detector? It seems like it would reduce the efficiency though.

"If I were winding coils, I would use copper."
You do wind coils right? I could swear I read somewhere you did. What gauge would you recommend for experimentation?

The reason I ask is I am learning as much as I can, it might be possible to wind a snooper 350 for the DFX. Why there is not one like this by White's or Excelerator I do not know.

Sorry to ask, kind of off topic. But there is an engineer in the room and I can't pass up the chance to learn something, forgive me!

In some single-frequency designs the transmit coil is part of the transmit oscillator and is therefore a resonant-tuned coil. But not so in many designs, and not so in all multi-frequency designs. The receive coil is almost always non-resonant in order to get a linear phase response needed for good target ID.

Yes, it is probably possible in many cases to take a coil meant for one design and force it to work with another. It may work well, and it may not. Here's a dirty little secret about White's coils: you can make a DFX/MXT coil work on a Prizm, and it works pretty darned good. Don't tell anyone. However, a Prizm-specific coil will not work well on a DFX.

Winding your own coils can be tricky, it's hard to get a good enough null and some coils need internal tuning caps. Generally, you want to match the inductance and get the resistance in the ballpark, and this determines # of turns and wire gauge. Typical VLF coils have more turns and smaller wire gauge on the RX coil than TX.

Practically everyone is using enameled copper wire because (1) it is easily available & cheap and (2) it works really really well. Silver wire would not add any practical benefits and your coils would end up stolen. Aluminum makes a lighter coil but oxidizes terribly so it is hard to make a reliable connection.

- Carl

 

[Carl-NC]

I tried to post a video of our new design but it didn't take. Oh well, guess you'll have to wait!

 

[Carl-NC]

See reply above...

 

[Terry B]

n/t

 

[d1g1man]

Oh yeah right! arrgghh, torture I say, torture!

I tried to post a video of our new design but it didn't take. Oh well, guess you'll have to wait!

 

[littletwig]

Since we are talking about coils here, I got a question. I use an M6 with the 6x10 DD and I feel I do quite well with it as far a depth go. Trash separation is a given. I consistantly find coins at 5-7 inches. Most everyone says that I am loosing depth with this coil on my M6. With this coil I can turn up the senc and run my desc to 0 and I run tones on. Am I really loosing depth with this coil and if so WHY. Will some of you tekies please give me some insite. Thanks.