Find's Treasure Forums
Welcome to Find's Treasure Forums, Guests!
You are viewing this forums as a guest which limits you to read only status.
Only registered members may post stories, questions, classifieds, reply to other posts, contact other members using built in messaging and use many other features found on these forums.
Why not register and join us today? It's free! (We don't share your email addresses with anyone.) We keep email addresses of our users to protect them and others from bad people posting things they shouldn't.
Click here to register!
Need Support Help?
Cannot log in?, click here to have new password emailed to you
Changed email? Forgot to update your account with new email address? Need assistance with something else?, click here to go to Find's Support Form and fill out the form.
Deleted by Cody
- Thread starter Cody
- Start date
Cody,
I think in the long run it would be best if we don't try to get too technical on these forums. So, usually, I will present replies in 'common speak' rather than technical terms. Usually.
"I know how modern discrimination works but am not sure of the early model TR detectors. Prior to discrimination a target was indicated by with constant tone but was due to induction of current in the receiver."... Because many will read these forums who are newer to the hobby, some replies folks post will go over some of the earlier types. Everybody just has to bear with it.
The early TR models, just like the VLF models today, all work on the TR (Transmit/Receive) principle. This is the same as IB (Induction Balance). The main difference is that they lacked what were refer to as a discrimination circuit, and they operated at much higher frequencies, usually around 100 kHz.
Most had a simple Metal/Mineral tuner control that allowed the operator to adjust to a 'null' point between ferrous (mineral) and non-ferrous (metal) mass. Due to the low response from most ground (which produces a signal of about 1 Hz to 2 Hz) combined with the very high operating frequency, those early TR's could be tuned such that they essentially ignored the ground as well as common iron nails.
This same basic principle was used in some early TR's that lacked the 'mineral' adjustment range and simple had a 'tuner' control, but also ignored small iron junk. All of those early models were responsive to small foil, medium foil, bigger foil, gold jewelry, nickels and on up to silver coins.
With ALL conventional TR detectors it is very important to maintain a very uniform coil-to-ground relationship. ALL target responses then, just as today, are based upon the changes in the electromagnetic field generated around the coil. The differences are how they are processed. Properly tunes, iron (or bad ground) will null out the TR from a threshold setting while a non-ferrous target will produce a more solid beep.
"How did the early TR discriminate.".. When we first got discriminating circuitry it came about due to the abundance of foil that was encountered, and some other lower-conductive junk. It did eliminate hearing good beeps from a lot of junk, but what we then had to do was listen for the nulling caused by the now-rejected low-conductive junk, also. Same principle, but the tuning set-up was now shifted a bit higher and at minimum discrimination models such as the Compass Judge still had more rejection or bias towards the ground signal than the Compass 77B, and they didn't work as well in iron nail trash as the 77B.
"We stated off by watching meter and using the width of targets."... Keep in mind that the early detectors with needle meters only provided a signal strength and, on occasion, battery test info.
The best information they could provide was signal strength, but any little extra info could help, or hinder, learning the detector. Using the audio response strength as well as the analog meter's signal strength display, we could do some sizing and shaping of a target, but that was about it.
"We could tell iron from other metals by moving the coil towards the target and watching the meter. If there was a slight dip in the needle just before it went positive then it was iron and if not then nonferrous."... Well, I have to differ with you on this. It all depends upon the target's make-up, size and shape, and the position from the coil. However, if you approach a non-ferrous target at about 3", for example, and you're listening to an audio threshold, you will hear a little audio increase, and then a notable decrease, and then a strong response from the target when the coil is basically centered over the target. If you used a ferrous target of similar size and shape, you would NOT get the nulling effect and, instead, get a more continuous audio response as the target is moved into the EMF, and a broader response as well.
This is due to the different effect ferrous and non-ferrous targets have on an electromagnetic field.
"We could also tell by the tone as a deep coin or tinfoil had a rounded mellow tone."... This I can agree on, but will clarify because some makes and models had/have audio responses that some of us can hear better than others.
"How did they discriminate between targets with the TR that indicates the likely ID on a meter before the VLF.?".... They didn't. We didn't have visual Target ID before we had VLF and VLF Disc. models. We did have decent discrimination.
Actually, we had much better discrimination with the conventional TR Disc. circuitry than what we have today with our modern VLF motion discriminators! The problems we had were that it was much more difficult to remain stable because as the operating frequency dropped the conventional TR mode operation because more squirrelly to coil-ground height variances. Then, too, as the level of discrimination increased, the TR operation was even more touchy to coil position changes!
But in non-mineralized or very low mineralized environments, the TR-Disc. circuits we had did a much cleaner job of rejecting target based upon their conductivity.
Motion-based models provide easier operation because they are both rejecting the ground mineral signal and doing some discriminating of unwanted trash, but... they do not have clean, progressive discrimination like the conventional TR models.
Monte
I think in the long run it would be best if we don't try to get too technical on these forums. So, usually, I will present replies in 'common speak' rather than technical terms. Usually.
"I know how modern discrimination works but am not sure of the early model TR detectors. Prior to discrimination a target was indicated by with constant tone but was due to induction of current in the receiver."... Because many will read these forums who are newer to the hobby, some replies folks post will go over some of the earlier types. Everybody just has to bear with it.
The early TR models, just like the VLF models today, all work on the TR (Transmit/Receive) principle. This is the same as IB (Induction Balance). The main difference is that they lacked what were refer to as a discrimination circuit, and they operated at much higher frequencies, usually around 100 kHz.
Most had a simple Metal/Mineral tuner control that allowed the operator to adjust to a 'null' point between ferrous (mineral) and non-ferrous (metal) mass. Due to the low response from most ground (which produces a signal of about 1 Hz to 2 Hz) combined with the very high operating frequency, those early TR's could be tuned such that they essentially ignored the ground as well as common iron nails.
This same basic principle was used in some early TR's that lacked the 'mineral' adjustment range and simple had a 'tuner' control, but also ignored small iron junk. All of those early models were responsive to small foil, medium foil, bigger foil, gold jewelry, nickels and on up to silver coins.
With ALL conventional TR detectors it is very important to maintain a very uniform coil-to-ground relationship. ALL target responses then, just as today, are based upon the changes in the electromagnetic field generated around the coil. The differences are how they are processed. Properly tunes, iron (or bad ground) will null out the TR from a threshold setting while a non-ferrous target will produce a more solid beep.
"How did the early TR discriminate.".. When we first got discriminating circuitry it came about due to the abundance of foil that was encountered, and some other lower-conductive junk. It did eliminate hearing good beeps from a lot of junk, but what we then had to do was listen for the nulling caused by the now-rejected low-conductive junk, also. Same principle, but the tuning set-up was now shifted a bit higher and at minimum discrimination models such as the Compass Judge still had more rejection or bias towards the ground signal than the Compass 77B, and they didn't work as well in iron nail trash as the 77B.
"We stated off by watching meter and using the width of targets."... Keep in mind that the early detectors with needle meters only provided a signal strength and, on occasion, battery test info.
The best information they could provide was signal strength, but any little extra info could help, or hinder, learning the detector. Using the audio response strength as well as the analog meter's signal strength display, we could do some sizing and shaping of a target, but that was about it.
"We could tell iron from other metals by moving the coil towards the target and watching the meter. If there was a slight dip in the needle just before it went positive then it was iron and if not then nonferrous."... Well, I have to differ with you on this. It all depends upon the target's make-up, size and shape, and the position from the coil. However, if you approach a non-ferrous target at about 3", for example, and you're listening to an audio threshold, you will hear a little audio increase, and then a notable decrease, and then a strong response from the target when the coil is basically centered over the target. If you used a ferrous target of similar size and shape, you would NOT get the nulling effect and, instead, get a more continuous audio response as the target is moved into the EMF, and a broader response as well.
This is due to the different effect ferrous and non-ferrous targets have on an electromagnetic field.
"We could also tell by the tone as a deep coin or tinfoil had a rounded mellow tone."... This I can agree on, but will clarify because some makes and models had/have audio responses that some of us can hear better than others.
"How did they discriminate between targets with the TR that indicates the likely ID on a meter before the VLF.?".... They didn't. We didn't have visual Target ID before we had VLF and VLF Disc. models. We did have decent discrimination.
Actually, we had much better discrimination with the conventional TR Disc. circuitry than what we have today with our modern VLF motion discriminators! The problems we had were that it was much more difficult to remain stable because as the operating frequency dropped the conventional TR mode operation because more squirrelly to coil-ground height variances. Then, too, as the level of discrimination increased, the TR operation was even more touchy to coil position changes!
But in non-mineralized or very low mineralized environments, the TR-Disc. circuits we had did a much cleaner job of rejecting target based upon their conductivity.
Motion-based models provide easier operation because they are both rejecting the ground mineral signal and doing some discriminating of unwanted trash, but... they do not have clean, progressive discrimination like the conventional TR models.
Monte