TDI coil pin out

[Mark-VA]

I recently purchased a small coil from a fairly well known detectorist on many of the major forums. He stated the coil was an OZ 7.5" mono coil, but when it came the labels were missing and using an ohm meter I believe the coil is actually a dual field 7.5" coil.
Needing a true mono coil is the reason it was bought. Well anyway ohm readings are slightly lower on the 7.5" coil over the 12" stock coil which is just what it should be.
Question: A true mono coil should only have one set of windings and use only 2 pins in the configuration, correct?
The dual field coil has two sets of windings and uses 3 different pins, correct?
So that being said this is most likely a dual field 7.5" coil.

Plug on bottom is the 7.5" coil
Is this most likely a dual field coil?

[Carl-NC]

The mono & DF both use 2 pins. The third pin is only unique on a DD coil.

[6666]

From Reg

All coil connectors are wired the same whether the coil comes with a TDI or a SL.
Pins 1 and 5 are shields or grounds. Pin 2 is the RX
and in the coil connector this needs to be tied to pin 4.
Pin 4 is the TX signal and on a mono coil needs to be tied to Pin 2.
Again, this is the coil connector pin layout.

[Mark-VA]

So how can I tell what this coil actually is?

[Geo]

Look here...

[Mark-VA]

I was wanting to know if the coil I received was a White dual field 7.5" or a Whites mono 7.5 OZ coil.
Any help would be great.

[Geo]

I will look at my 7.5" DF coil if it writes something about DF and will answer to you

[Geo]

Markg see your PM...

[kt315]

I was wanting to know if the coil I received was a White dual field 7.5" or a Whites mono 7.5 OZ coil.
Any help would be great.

Mark, DF coil is MONO. DD is splitted in TWO parts - TX and RX. so your mistake you confuse two
different matters.

[Carl-NC]

Mark, DF coil is MONO. DD is splitted in TWO parts - TX and RX. so your mistake you confuse two
different matters.

Mark didn't ask anything about a DD coil, he wants to know whether the coil is mono of DF. While DF is technically a mono, it has 2 different coils in it.

Mark, try this... take a very small, like a 1/4" square of foil. It should only be detectable if you literally rub it on the perimeter where the coil is at. Rub it on the plastic where the inside coil should be. If you get a response, it's a DF. If you don't, it's a mono.

[Geo]

Carl the DF coil writes on it.. "TDI Dual Field 7.5".
I suppose that the mono 7.5 don't write DF...

[kt315]

So how can I tell what this coil actually is?

it looks like VLF coil but is not VLF certainly. it is dual fieil - dual windings splitted in inside and outer parts.

[Mark-VA]

Thanks Carl for the tip on determining mono or DF. The coil is definitely a dual field. It sounds off on both coil locations.
I'm very disappointed in the guy who sold it to me.
Being the fact the coil had no markings was my first clue that something was amiss.
I took a magnifying glass and I can see where a tag might have been.
It is amazing what people will do at times.

All is not lost though, the main reason I was wanting a mono coil was to hunt the old school sites where they dumped out their coal waste. I might add the 12" dual field has found many undetectable relics and silver (not detectable by VLF machines). Increasing the delay on my SL was the key to finding keepers in these areas.

Below is a post I made a while back on what was found.

After several hours hunting with the TDI SL I finally found the perfect settings for this particular site. This place is littered with the waste bi-product of burnt coal over many years. Much of the waste is small in size, ranging from BB to marble size and the smaller pieces easily attract to a magnet. In addition to that, the area is littered with nails ranging from 1 to 4" in length and some up to 4" deep. These nails, especially the larger ones give a good audio, especially with a ground balance of 8-9. After a suggestion from Reg, I began adjusting the GB to 4-5 and if the signal became inconsistent then the target was most like a nail. After a lengthy amount of hunting I decided to run the machine at gain max, pulse 10 and GB of exactly 5. Surprisingly the false signals all but stopped and I started finding old copper pennies some being wheat pennies in an area where I had gridded off and cleaned out of all good targets. Amazingly, I still can't believe I had missed that many targets with my other machines.
Now my next plan is to locate, what I believe to be good non-ferrous targets with the SL and mark each location. Then use my regular VLF machine and see if I can detect each target and note the audio responses given. Many things to consider in this journey. Very excited to say the least.

Well, went back to the same site where I posted, "perfect settings for this site" and hunted a small area not more that 60' from the prior hunt. Used the same settings "GB 5, pulse 10 and gain max" and off I went. After a short while I noticed a lot of clipped or inconsistent audio reports. Decided at that point to reduce gain to 7 and continued. Hunted a few more feet, still clipped audio, strange, so I stopped to analyze the area a little more closely. Sweep in one direction and get a some what good audio, but the return sweep was either silent or chatter. Suspecting something was the cause I stopped and increased the pulse delay up a tad, nothing changed. Continued to increase the pulse until I reached 17 and suddenly the audio came through as a loud, almost overload low tone. Thinking it might be a nail, I dug and out comes a copper penny at less than 4" deep. Now to say the least, I was excited and puzzled.
Decided to start over where I started hunting and experiment using a pulse rate of 17. A few moments later came the same type of loud low tone. Thinking there is no way I missed that one my first pass I changed the pulse to 10 and the signal all but disappeared. Increased the pulse to 20 this time and spent over 5 minutes rotating around this target checking from every possible angle to see what might be causing the anomaly, switched the conductivity switch to all and still a consistent low tone with nothing else mixed in. Now one must keep in mind I'm using the stock 12" and at times it is very difficult to exactly pinpoint where the target actually is. Changed the pulse to 10 and and the low tone practically disappeared. Now I was wishing I had brought my Deus to recheck some of these inconsistent signals, maybe next time. Well anyway I dug a nice plug and out comes a wheat penny at less than 5" deep. Excited to recover something from an area that quit producing years ago.
Continued hunting with settings of pulse 20, GB 5 and gain at 7, and found many more coins dated in the early 60's all within a 3' path some 60' long.


Well anyway, at least I got a working coil for the $75.

I still believe a mono coil is the key to hunting these site so I'll keep looking.
I might add, I've had several of my hunting buddies comment on why I would chose to hunt with a PI and not my VLF machine, but the answer is the same, "In my opinion there is no perfect machine for every possible site on the planet" and the PI works very well at a few locations.

Mark didn't ask anything about a DD coil, he wants to know whether the coil is mono of DF. While DF is technically a mono, it has 2 different coils in it.

Mark, try this... take a very small, like a 1/4" square of foil. It should only be detectable if you literally rub it on the perimeter where the coil is at. Rub it on the plastic where the inside coil should be. If you get a response, it's a DF. If you don't, it's a mono.

[Geo]

This is my 7.5"

[Geo]

another photo