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Threshold Info.....

A

Anonymous

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I noticed on another forum....(not the Dumpo:) that MIke Hillis had asked about better understanding the threshold. This was a great question, as I have always labeled it like a second sensitivity being so non-technically inclined <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)"> But, he got a response from the legendary George Payne & I thought it would be a good read here too. Not sure I'm policically correct to copy this to here, but hey it was a question about the Coinstrike & this is a C$ class right? <img src="/metal/html/biggrin.gif" border=0 width=15 height=15 alt=":D">
>>>>
A threshold adjustment works differently than that of a sensitivity adjustment. The threshold setting reduces detector gain by
 
Are detectors made/ set up/wired , or whatever you call it that don't have a threshold you can tune, how do they compensate for it, many work very good,including Fisher,, without threshold tuning and ground balance, HOW THEY DO THAT??? HUH???? <img src="/metal/html/confused.gif" border=0 width=15 height=22 alt=":?"> <img src="/metal/html/confused.gif" border=0 width=15 height=22 alt=":?"> <img src="/metal/html/confused.gif" border=0 width=15 height=22 alt=":?"> <IMG SRC="/metal/html/flag.jpg" BORDER=0 width=32 height=17 ALT="usa~"> <IMG SRC="/metal/html/fisher.jpg" BORDER=0 width=60 height=13 ALT="f~"> <IMG SRC="/metal/html/fisher.jpg" BORDER=0 width=60 height=13 ALT="f~"> <IMG SRC="/metal/html/fisher.jpg" BORDER=0 width=60 height=13 ALT="f~"> <IMG SRC="/metal/html/usmc.gif" BORDER=0 width=19 height=21 ALT="usmc">
 
Thats not enough information and I have asked for some clarification between postive and negative threshold settings.
The other replies also confused me.
My understanding of detector gain is that there are usually two gain settings, Disc mode gain and All Metal gain. The sensitivity setting then acts like a squelch control on a cb radio. You adjust squelch to determine how strong a signal needs to be to 'break' squelch. Its used mainly for stability.
When I thought of Threshold, I wasn't thinking of a squelch control. I was thinking more along the lines of a signal dampner.
I noticed that positive threshold is detrimintal to performance in Disc mode, but adds performance in all metal.
Still need more information to know how to properly use it.
Happy CoinStriking <img src="/metal/html/lol.gif" border=0 width=15 height=15 alt=":lol">
MIke
 
illegally <img src="/metal/html/nono.gif" border=0 width=22 height=19 alt=":nono"> haa ha <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)">
But your right, I don't think the responses are really geared towards the C$. More threshold basics. I've seen those dis the C$ over there, but they do like the Excel alot. Seem similar to me <img src="/metal/html/shrug.gif" border=0 width=37 height=15 alt=":shrug"> The C$ threshold maybe be something totally different than most other units. Again, I have no technical clue at all.....Besides the C$ is "proprietary" or top secret <img src="/metal/html/blush.gif" border=0 width=15 height=15 alt=":redface">
 
Here is another response geared to my understanding of the gain control and sensitivity, where I asked if I have two "squelch" controls.
<span style="background-color:#ffff00;">"Please keep in mind that my comments relate to my own design experience. Other designers may use different techniques to determine detector sensitivity.
I have always used the threshold process to control motion gain. The threshold technique used to control motion gain
 
this is not from fisher but it does get more technical
http://www.ionet.net/~tgomez/threshold.html
 
Hi Bugar,
Preset GB silent search machines are a compromise. Basically from what I understand, the circuit is set up so that you will never (well almost never) hear any response from the ground signal caused by mineralization even though it is always there and the detector has to deal with it. As most know this type of machine does not work all that well in iron mineralized ground and can lose a lot of depth. The problem with most silent search detectors is that a lot of people will never know when the ground is killing the depth. It was all done in a effort to make Detectors easier for more people to use with as few problems as possible, other than the aformentioned iron ground problem.
George Payne, who Bill plagerized above <img src="/metal/html/lol.gif" border=0 width=15 height=15 alt=":lol"> stated at one time that he was hesitant to give in and switch to silent search preset GB machines in some of his designs. Only because the competition was doing it and the company he worked for needed it to compete.
Tom
 
This is the theory I am going to procede with for the CoinStrike.
I am going to assume that Sensitivity is more like a pre-amp signal gain control. This makes sense to me because the higher the setting,the more it amplifies all signals, including electrical interference. It affects all signals equally.
Threshold is the actual signal strength control. At a "0" setting it is optimized. At a +1 setting it is enhanced. Further postitive settings begin to drown out the lower conductive signals due to audio strength. As the threshold is decreased, a signal requires a stronger response to still register. At a -95 setting, only a specific strength signal will register, as the threshold is moved toward positive, weaker signals are boosted toward the audio registration level.
Look out!
Happy CoinStriking <img src="/metal/html/lol.gif" border=0 width=15 height=15 alt=":lol">
Mike
 
I figured it must be some kind of compromise <img src="/metal/html/glasses.gif" border=0 width=15 height=15 alt=":geek:">
 
I believe the threshold on the CS$ in not the same as what other machines have. I've used many and still have two that needs a threshold hum. You can tell that their threshold is reacting to the ground and targets. The hum on the CS$ at positive settings is strange. It don't change with targets or the ground and I haven't found any reason to use the positive threshold at all. On these other machine, lowering the threshold below audio dosn't help me run higher sens. at all. It does on the CS$. I still don't know why Fisher called this adjustment a threshold.........
HH'n
 
it does pose the question is there more to the threshold than simply being a setting that triggers an audio response?
I did find it interesting that George mentioned that using "threshold" based sensitivity on his designs allows a high circuit gain to be used.
I quess it depends on the type of circuit as to what affect high gain has on a detectors discrimination abilities. The old analogy of using high beams in a fog to me meant lowering circuit gain for best results. Now that "threshold" based sensitivity enters the picture it does confuse the issue. <img src="/metal/html/lol.gif" border=0 width=15 height=15 alt=":lol">
I am going to spend some time as Kevin has done comparing threshold settings with high sensitivity and I am betting he has something there.
Tom
 
I have read on this forum that to get the best depth the threshold should be set around 0. Another post said quote "I have found that my machine will gain depth on deep unplanted coins by lowering the threshold" (not sure who I plagerized this from <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)"> Which is true and do soil conditions play a factor?
 
I think it said by increasing it then you will start chopping away at depth.
 
Hey Mike, I think the person to ask is TY BROOKS. He does Tech Talk for Western/Eastern Treasures Magazine, but I don't know his e-mail address. I know he has an e-mail address, I just don't know it!
HH, GOOD LUCK, NamVetLesTreasureSeeker
 
When you attribute the original source of where you get
your information it is not considered plagerism; when you don't give a source for something, and try to pass it off as your own, then it is plagerism.
 
Thanks NamVet,
I'll find a way to look him up.
In the meantime I have a series of airtests to do to see what the corrolation is between the two features.
Happy CoinStriking <img src="/metal/html/lol.gif" border=0 width=15 height=15 alt=":lol">
 
If the threshold is set to high, it will mask the deepest signals. You can verify this in tests.
Originally the threshold was used on VLF/TRs to ground balance, and to let you know if your detector drifted.
I believe the main reason to use in on most motion detectors is to let you know if you pass over something that is 'disced' out. It seems to work on the C$ somewhat as the silencer is used on the 1270 & 1236X-2.
You can also for example, turn up the GAIN all the way, on an MXT, and if you have noise, lower the threshold to where the noise disappears, while getting the benefit of full sensitivity.
My spy at FISHER also tells me they are working on a new chip. Could it be a non motion hunting mode...???
<img src="/metal/html/confused.gif" border=0 width=15 height=22 alt=":?">
 
he was just talking about threhold principles in general & probably never used a C$. The C$ may be completely different. It's "proprietary" <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)">
 
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