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Trying To Find True Mono For TDI


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I have tried for 4 years to find a true mono "oz" coil for my White's TDI. Had one guy sell me the 7 1/2" White's coils for an OZ coil but it turned out to be the White's TDI dual field coil according to one of the engineers that worked at White's. Some of the areas where I hunt have harsher ground than the red dirt in northern Virginia. This is man made issues because of the coal slack (that easily attracts to a magnet) discarded over many decades in these areas. The TDI has found many targets that the best VLF machines could only ID as iron.

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6 hours ago, Mark Gillespie said:

Had one guy sell me the 7 1/2" White's coils for an OZ coil but it turned out to be the White's TDI dual field coil according to one of the engineers that worked at White's.

I have the 12" Oz mono coil because it came stock with all TDI SPP's.  It's easy for that size coil to tell if it's dual field or simply mono -- just bring a hand-held pinpointer tip close to the inner round ring and see if it squeals.  (Mine is silent.)  I don't know if that's a telltale sign for the 7 1/2" size but you could try that.

I really like the 12" OZ mono as it's quite lightweight for its size (512 g = 18 oz or 1 lb 2 oz w/skidplate) but sorry to have to tell you it's staying with me.  (As I think, is this the one I loaned you for a short time?)  I doubt many were sold individually here in the USA and pretty sure the other White's TDI models here were outfitted with the dual field 12" (if they shipped with 12" coils at all, that is).  Might be easier to find one in Australia but then have to pay through the nose for shipping.  :sad:  I assume you checked with Centerville Electronics (official repair site for White's).  They have a 12" TDI coil listed there but it doesn't say which variety so likely the dual field.  Might know of one salted away though?

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Thanks I'll send them an email.  Don't remember ever getting to try the mono coil.  But Nelson sent me the miner john coil to try years ago.

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  • The title was changed to Trying To Find True Mono For TDI
2 hours ago, Steve Herschbach said:

People confuse coils a lot and the dual field is a unique coil so even easier to confuse. The guy may have honestly thought he was selling you a mono.

Here's a question for you, Steve. Does the TDI setup use separate transmit/receive coils, or do they use a single coil for both functions? I'm assuming, if they use a single coil for both, than the DF coils are simply a mono coil that splits the mono into two separate coils wired in series.

Jim

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19 minutes ago, Jim in Idaho said:

Here's a question for you, Steve. Does the TDI setup use separate transmit/receive coils, or do they use a single coil for both functions? I'm assuming, if they use a single coil for both, than the DF coils are simply a mono coil that splits the mono into two separate coils wired in series.

Jim


They are mono in the sense they alternate as both transmit and receive coils. Otherwise they would be concentrics, one winding transmitting, the other receiving.

We have mono and dual field mono, concentric, DD and Focused Core variants on the PI market, plus the now discontinued folded mono made by Miner John.

“A new dual field search coil for pulse induction metal detectors has multiple coplanar wire coils of different diameters connected in series…”

 

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I understand the difference between a DF and standard mono. Maybe I phrased my question wrong. What I'm confused about apparently, is the difference between true mono's and most others. Another question is "are the DF's just another form of mono?

Jim

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I did a bit of research and answered my own question. So, for clarification for people who aren't as dumb, or inquisitive as I am here's what I wanted to be sure of. All PI's use a single coil for both transmit and receive. But, and it explains my confusion, that single coil, for both purposes, may be divided up into several coils, or even more than one circuit, inside the detector. That was the basis for my confusion regarding the use of the term "mono" when it comes to differentiating the various coil types. It's interesting the Reg Sniff called his design a "folded" mono. Electrically, there's little difference between that and White's DF design. They both use that one circuit to the coils to accomplish both Trans, and Rec.. but both divide that coil circuit into separate coils.

Jim

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I included the link to the patent information to answer exactly what the DF coils are, but yes, basically they are just mono coils. Mono does not mean a single round loop of wire. That’s just the most common and simple way to do it. Mono is about a single winding alternating as a transmit and receive, not how the winding is laid out. “Not mono” means the is one winding acting as a transmit and another as a receive. Combined alternating functions in one winding (mono) versus functions separated into dedicated windings (not mono). Which is what I said in my first answer assuming people knew that I guess. :smile:

 

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My recollection is Reg's and then miner John's 'folded mono' design, folded single coil,  was to avoid White's patent for the dual field where "multiple coplanar wire coils of different diameters connected in series...". From what I read Miner John's coil seemed to get great reviews and in high demand. Have any other coil manufacturers followed up on either the White's or folded mono designs and were there any real advantages over the single loop mono?

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