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Exactly what does the threshold do?
- Thread starter pvtcook
- Start date
This threshold explanation was once offered by Mike Hillis with the F5 as an example. It should be the same theory with all F series. Think of threshold as a doorway with zero threshold being a door wide open. Each minus setting from -1 to -9 will close the door a little more with each setting. On the other hand a +1 through+9 setting will actually amplify the signal respectively. I find the negative threshold numbers seem to help eliminate small unwanted target signals like small bits foil, can slaw, or those coming from the final breakup stages of rust that is associated with big iron. Minus threshold along with reduced sensitivity work well together in taming the spirited F70 in my case and actually seem to reduce the coils footprint in high trash areas. As an example I once got a one way hit on a 6" deep Mercury dime with a -3 threshold and 35 sensitivity setting with the F70----------Hope this helps--------IB
Here is my take, FWIW.
True threshold is a sensitivity control for the receiver on the coil. The transmitter of the coil on the F5 (for instance) is controlled by the gain. If you have a gain function on your unit, you can use both in AM as well as DISC. But most detectors have a constant gain preset. That is, the coil transmiiter just emits one strong uncontrolled signal. And the return signal is only controlled with the sensitivity (threshold really does nothing unless in AM). Or at best, it is just a fine tuner, so to speak, within the area the sensitivity control is set at.
Threshold in AM, is the sensitivity setting for listening to the ground. In AM, you set the threshold to a slight hum, picking up the metals already in the soil (mineralization). When swinging, any metal change (even a small peice of foil the size of a pencil eraser) will change the constant hum slightly. There is not enough signal to activate the segment ID or maybe even the numerical ID. So the ears pick up this slight change over the detectors electronics trying to identify it. This allows for smaller and also deeper seeking metrics. And coin at 12" on my F5, can be distinguished with a tone (hum) change, but never show up in the ID if I'm in DISC. Once I can get closer to the coin with the coil (9") the ID then has enough signal to attept identification.
AM means what it says. All metal, identifiable or not, with deeper possibilties.
True threshold is a sensitivity control for the receiver on the coil. The transmitter of the coil on the F5 (for instance) is controlled by the gain. If you have a gain function on your unit, you can use both in AM as well as DISC. But most detectors have a constant gain preset. That is, the coil transmiiter just emits one strong uncontrolled signal. And the return signal is only controlled with the sensitivity (threshold really does nothing unless in AM). Or at best, it is just a fine tuner, so to speak, within the area the sensitivity control is set at.
Threshold in AM, is the sensitivity setting for listening to the ground. In AM, you set the threshold to a slight hum, picking up the metals already in the soil (mineralization). When swinging, any metal change (even a small peice of foil the size of a pencil eraser) will change the constant hum slightly. There is not enough signal to activate the segment ID or maybe even the numerical ID. So the ears pick up this slight change over the detectors electronics trying to identify it. This allows for smaller and also deeper seeking metrics. And coin at 12" on my F5, can be distinguished with a tone (hum) change, but never show up in the ID if I'm in DISC. Once I can get closer to the coin with the coil (9") the ID then has enough signal to attept identification.
AM means what it says. All metal, identifiable or not, with deeper possibilties.
MarkCZ
Well-known member
The old term of "Threshold" and adjusting it was nothing more than setting a running (operation) tone which meant a constant low volume hum.
Now days that's still somewhat true but there is a little more of a breakdown to it.
If the F75 in this area is like the F5 and units like the Coinstrike then the Gain is the sensitivity to the coils detection circuit, while the "threshold" is the control (trigger) for the audio circuit (audio amp). The threshold adjust the sensitivity to the audio amp to signal a response from the incoming detection circuit, the higher the minus number the stiffer the amp is to respond (its takes more to set it off) the closer to zero you get the jumper the amp is to respond to even circuit noise and other interference, more to the plus numbers and you (with some models) may move from the realm of silent search into a running tone of some sort, in models like the Omega the manual calls this (Running into the noisy range) and is only recommended for very experienced users.
Mark
Now days that's still somewhat true but there is a little more of a breakdown to it.
If the F75 in this area is like the F5 and units like the Coinstrike then the Gain is the sensitivity to the coils detection circuit, while the "threshold" is the control (trigger) for the audio circuit (audio amp). The threshold adjust the sensitivity to the audio amp to signal a response from the incoming detection circuit, the higher the minus number the stiffer the amp is to respond (its takes more to set it off) the closer to zero you get the jumper the amp is to respond to even circuit noise and other interference, more to the plus numbers and you (with some models) may move from the realm of silent search into a running tone of some sort, in models like the Omega the manual calls this (Running into the noisy range) and is only recommended for very experienced users.
Mark
I've been running mine on +1. In some areas when I'm sweeping the coil I get a whooomp whooomp sound evrytime I sweep the coil. It gets on my nerves and I have to switch to Disc mode. I have never been able to figure out why it does that. Could it be my threshold is too high?
Mike Hillis
Well-known member
Please thank Tony Gomez and the long lost "Tony's Bandido II Umax Site, for the following information.
HH
Mike
.
.
Threshhold-the reason why
--------------------------------------------------------------------------------
The reason behind having a threshhold, is to basically compensate and calibrate the detector for it to work properly.......Why? Well lets start off at the beginning, I believe that if, you the reader , understand the reason why you have to set a proper threshhold, it will be easier in setting up the threshold. It is the base setting that the rest of your initial setup of the detector will depend on, and I believe it is important enough to have a better understanding. The setting of a threshhold is basically compensating for differences of electronics, the differences in human anatomy/quality of one's hearing, and our individual preferences.
[attachment 294029 thresh1.gif]
Threshhold refers to a phenemonon of the silicon transistor. One of its characteristics is that it will not conduct until the magic voltage of 0.7 volts is exceeded.Once it exceeds this voltage, the transistor will then begin to conduct and amplify any signal. The final output stage consists of a final audio transistor with two input sources. One from the audio oscillator and one from the filtered detected signal output. When we say filtered detected signal output, a network of 2 or 4 pole capacitor filters that take the amplified detected signal and make it a DC(direct current) This is the basis of one of the inputs to the transistor. The second is the audio oscillator-this is the tone we hear coming out of the detector.(NOTE: the audio coming out of the control box is not the "operating frequency" of the detector-this normal "operating frequency" is around 10khz thats 10,000 hertz and would be almost a high screech- almost impossible to hear -the audio oscillator's frequency is probably around 800-1200 hertz-I havent actually measured it but as a radio tech for many years and having the ability to whistle a 1khz tone-the standard test tone to test a radio- is kinda like a job requirement - )
[attachment 294030 thresholda.gif]The pic on the left illustrates the the principle and basis of a induction balanced metal detector's threshold. The yellow portion represents the filtered output from the recieve amplifiers output- with no signal/aka target present.of course the grey wall represents our "threshold" of the final audio amplifiers transistor. The signal level of the audio transistor is not large enough to exceed the threshold, and we have no audio signal out. This also would be representative of when the threshold is turned fully counter clockwise. When we adjust the threshold we are actually inserting an additional dc bias into the input or base of the transistor, this allows the audio oscillator's signal to exceed the threshold and be amplified in a logarimthic way.This would be equivalent to tuning the threshold clockwise until we hear an audible constant hum.
[attachment 294031 Threshold.gif]
In a nutshell the tuning of the threshold will actually is compensating for the differences in our hearing, because no two human beings posses the same quality of hearing. What may be loud to some one , may be too soft for another person. Another way it compensates is for personal preferences, some people like the threshold to be a little louder, and some people like it a little softer. I personally like the threshold just loud enough to not having to strain to hear it i.e. not too loud, and not too soft. This, is like I said, a matter of personal preference. In conclusion the threshold compensates for the slight differences in the electronics, the slight differences the way the coil was constructed(no two coils are alike), and the differences in the individuals human ears. Setting the threshold is important, because the rest of the detector set up is determined and based on the setting.
HH
Mike
.
.
Threshhold-the reason why
--------------------------------------------------------------------------------
The reason behind having a threshhold, is to basically compensate and calibrate the detector for it to work properly.......Why? Well lets start off at the beginning, I believe that if, you the reader , understand the reason why you have to set a proper threshhold, it will be easier in setting up the threshold. It is the base setting that the rest of your initial setup of the detector will depend on, and I believe it is important enough to have a better understanding. The setting of a threshhold is basically compensating for differences of electronics, the differences in human anatomy/quality of one's hearing, and our individual preferences.
[attachment 294029 thresh1.gif]
Threshhold refers to a phenemonon of the silicon transistor. One of its characteristics is that it will not conduct until the magic voltage of 0.7 volts is exceeded.Once it exceeds this voltage, the transistor will then begin to conduct and amplify any signal. The final output stage consists of a final audio transistor with two input sources. One from the audio oscillator and one from the filtered detected signal output. When we say filtered detected signal output, a network of 2 or 4 pole capacitor filters that take the amplified detected signal and make it a DC(direct current) This is the basis of one of the inputs to the transistor. The second is the audio oscillator-this is the tone we hear coming out of the detector.(NOTE: the audio coming out of the control box is not the "operating frequency" of the detector-this normal "operating frequency" is around 10khz thats 10,000 hertz and would be almost a high screech- almost impossible to hear -the audio oscillator's frequency is probably around 800-1200 hertz-I havent actually measured it but as a radio tech for many years and having the ability to whistle a 1khz tone-the standard test tone to test a radio- is kinda like a job requirement - )
[attachment 294030 thresholda.gif]The pic on the left illustrates the the principle and basis of a induction balanced metal detector's threshold. The yellow portion represents the filtered output from the recieve amplifiers output- with no signal/aka target present.of course the grey wall represents our "threshold" of the final audio amplifiers transistor. The signal level of the audio transistor is not large enough to exceed the threshold, and we have no audio signal out. This also would be representative of when the threshold is turned fully counter clockwise. When we adjust the threshold we are actually inserting an additional dc bias into the input or base of the transistor, this allows the audio oscillator's signal to exceed the threshold and be amplified in a logarimthic way.This would be equivalent to tuning the threshold clockwise until we hear an audible constant hum.
[attachment 294031 Threshold.gif]
In a nutshell the tuning of the threshold will actually is compensating for the differences in our hearing, because no two human beings posses the same quality of hearing. What may be loud to some one , may be too soft for another person. Another way it compensates is for personal preferences, some people like the threshold to be a little louder, and some people like it a little softer. I personally like the threshold just loud enough to not having to strain to hear it i.e. not too loud, and not too soft. This, is like I said, a matter of personal preference. In conclusion the threshold compensates for the slight differences in the electronics, the slight differences the way the coil was constructed(no two coils are alike), and the differences in the individuals human ears. Setting the threshold is important, because the rest of the detector set up is determined and based on the setting.
MarkCZ
Well-known member
Mike that's good information but that's more of adjusting the "threshold" level, the starting point, or the running tone of detectors like the Tesoro's. Its used for the all metal modes of those units. In the newer models, or ones like the F75, F5, and the Coinstrike I mentioned the threshold is a little more than that because the mentioned units are silent search and the threshold adjustment on these is not for an all-metal running tone.
The Coinstrike was one of the first units to operate like this (that I know of????) and people had a really hard time operating it because of the learning curve at the time around the "threshold". People wanted to hear a running tone and do that you had to go to the plus side of "O" but in many places the unit wasn't stable enough to run it with that hot of a setting, any noisy in the electronic detection circuit would "trigger" the audio amp.
So, adjusting the threshold on the Tesoro's or models like that and many of the older units is a bit different than the ones were taking about (as I understand it)
On models like the mentioned Tesoro's the threshold is the entrance point of the audio, or the point of where slight audio is heard.
On the F75/F5 and Coinstrike the threshold is the trigger (gate if you like) adjustment of the audio amp's to signal a report from the detection circuit, being these models are silent search with no running tone. So, a threshold In the minus number sets a "stiffer" trigger or gate for the audio amp's input, closer to "0" and the audio amp's trigger or gate gets very touchy like a hair trigger on a pistol.
Mark
The Coinstrike was one of the first units to operate like this (that I know of????) and people had a really hard time operating it because of the learning curve at the time around the "threshold". People wanted to hear a running tone and do that you had to go to the plus side of "O" but in many places the unit wasn't stable enough to run it with that hot of a setting, any noisy in the electronic detection circuit would "trigger" the audio amp.
So, adjusting the threshold on the Tesoro's or models like that and many of the older units is a bit different than the ones were taking about (as I understand it)
On models like the mentioned Tesoro's the threshold is the entrance point of the audio, or the point of where slight audio is heard.
On the F75/F5 and Coinstrike the threshold is the trigger (gate if you like) adjustment of the audio amp's to signal a report from the detection circuit, being these models are silent search with no running tone. So, a threshold In the minus number sets a "stiffer" trigger or gate for the audio amp's input, closer to "0" and the audio amp's trigger or gate gets very touchy like a hair trigger on a pistol.
Mark
Mike wow!!! That was 3 miles over my head!! If I understand correct. If I run the threshold in the minus numbers that means that it takes a stronger signal to set of a beep and the + numbers will sound off easier? Right ? If I back the threshold off will it stop the whooomp whooomp sound as I swing the coil? It's very annoying.
Mike Hillis
Well-known member
pvtcook,
Yep...you got it right.
I don't think the threshold setting will affect your Whoomp responses, though.
If you are correctly balanced to the ground, in the All Metal operating mode, metal objects should be giving more of a zip zip sound, not a whoomp whoomp sound. That sounds more like an incorrect ground balance, or you are getting feedback from negative hot rocks.
Can you pinpoint the whoomp responses or are they phantoms? You get the response but there is nothing there?
I'd check your ground ground balance. After you balance, raise your coil, pull the pinpoint trigger and lower the coil to the ground. If you are balanced correctly you should not hear any threshold change as your lower your coil to the ground.
Negative hot rocks (cold rocks) give a elongated response after you have already passed over them. They could whoomp, or bong response. If you can identify this response to one of those rocks, and if you have a lot of them, you could try ground balancing to it and see it that helps.
Good luck.
HH
Mike
Yep...you got it right.
I don't think the threshold setting will affect your Whoomp responses, though.
If you are correctly balanced to the ground, in the All Metal operating mode, metal objects should be giving more of a zip zip sound, not a whoomp whoomp sound. That sounds more like an incorrect ground balance, or you are getting feedback from negative hot rocks.
Can you pinpoint the whoomp responses or are they phantoms? You get the response but there is nothing there?
I'd check your ground ground balance. After you balance, raise your coil, pull the pinpoint trigger and lower the coil to the ground. If you are balanced correctly you should not hear any threshold change as your lower your coil to the ground.
Negative hot rocks (cold rocks) give a elongated response after you have already passed over them. They could whoomp, or bong response. If you can identify this response to one of those rocks, and if you have a lot of them, you could try ground balancing to it and see it that helps.
Good luck.
HH
Mike
Mike Hillis
Well-known member
Hi Mark,
Tony did an excellent job of describing the threshold. They all work this way, the only difference being the circuits they are placed on and the names given to them. But the basic operation is the same. I like Tony's graphs as they show what is actually taking place and explain it on a technical level.
I don't see any conflicting information in your responses. You are saying the same thing, just using different words.
HH
Mike
Tony did an excellent job of describing the threshold. They all work this way, the only difference being the circuits they are placed on and the names given to them. But the basic operation is the same. I like Tony's graphs as they show what is actually taking place and explain it on a technical level.
I don't see any conflicting information in your responses. You are saying the same thing, just using different words.
HH
Mike
Mark you've pretty much nailed it, as relates to the new Fishers.
In the old days it was a low hum one listened to, which would vary in amplitude over a target.
Deep targets would give a minute increase in the tones amplitude - that is what old timers mean when they talk about "listening for whispers."
Shallow targets would overcome the threshold by a long margin, and kick in the discrimination circuits.
Today, we don't really need the old threshold, unless:
1. hunting in clean ground...
2. for very deep target, or tiny targets
3. In ALL METAL
Gold seekers still use it this way. For the rest of us, with our powerful discriminators, it isnt really needed any longer.
For my F70, I've begun thinking of it as the "trigger" you mention.
In the old days it was a low hum one listened to, which would vary in amplitude over a target.
Deep targets would give a minute increase in the tones amplitude - that is what old timers mean when they talk about "listening for whispers."
Shallow targets would overcome the threshold by a long margin, and kick in the discrimination circuits.
Today, we don't really need the old threshold, unless:
1. hunting in clean ground...
2. for very deep target, or tiny targets
3. In ALL METAL
Gold seekers still use it this way. For the rest of us, with our powerful discriminators, it isnt really needed any longer.
For my F70, I've begun thinking of it as the "trigger" you mention.
MarkCZ
Well-known member
Mike Hillis said:
Well, its all about better understanding of the threshold. Its clearer for me in one way as far as the silent search models vs ones that to have a audible operating threshold tone set different for each person level of hearing.
So, setting the trigger (trigger pull) of the audio amp and how easy or how stiff it is to alarm to a response from the detection circuit just helps some understand it.
And your right its all about voltage and Tony did a good job and thinks for posted that information!
Mark
Mark
Mike Hillis
Well-known member
Welcome back, David 
Mark in NC
Member
n/t
Charlie P. (NY)
New member
The threshold tone would also dive or disappear over iron and rise for non-ferrous.
I don't play much in All Metal with my F-75 but have found if I set it to just audible and then one click less it works out pretty well. How easy it is to get used to silent search and now find that background pitch annoying. ;-) At least in my case.
I don't play much in All Metal with my F-75 but have found if I set it to just audible and then one click less it works out pretty well. How easy it is to get used to silent search and now find that background pitch annoying. ;-) At least in my case.