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E-Trac kHz setting???

AVXVA

Member
In my experience, in Conduct mode, Channel 1 and 2 are the best. However, Channel 1 is often unavailable due to EMI.

In Ferrous mode, Channel 3 and 4 seem best.

The differences are only apparent when running the machine flat out (hot as possible: 27, 28, 29.) And you have to be set on 1-Tone or 2 Tone. Multi seems to have much less depth.
 

Chris(SoCenWI)

Well-known member
My turn....

We debated this all the time in the old days. I didn't watch the video in this thread but others I've seen are pretty much BS.

Yes, if you have a single frequency detector there will be a difference in response to different targets if you change the operating frequency from 1.5khz to 100khz.

But, that is not how it works in the FBS world. They transmit square wave pulses of two frequencies, and use where they mate up to generate the 17 (methinks) frequencies spread from roughly 1.5khz to 100khz. When you do a noise cancel or change the frequency number you are changing the frequency (and maybe period) of one of the square waves by a small amount. Now maybe they may mate up from 1.6khz to 101khz going from channel 1 to 2. All numbers I'm using are pretty much made up, I don't know the exact values. Anyhow even going to channel 11 is only going to shift the frequency slightly, say perhaps 2khz at the bottom end. Going from 1.5k to 2k is not going to have much if any affect on target response.

They reason for noise cancel and channel selection has nothing to do with ground mineralization or optimizing target response. Only to try get away from EMI; in the US and Canada primarily harmonics of 60hz, the rest of the world 50hz.

Long ago I read many of the patents and if I remember correctly the FBS detectors don't even bother to process frequencies that land close 50 or 60 hz harmonics. Generally I've only been able to bump sensitivity one or two notches after a noise cancel, but occasionally you may encounter an EMI source that is not related to the power grid; say a electric dog fence of someone else's detector, then it can make a considerable difference.

Chris
 

AVXVA

Member
Wow......

So according to Chris, (1) the expert (2) hired by Minelab (3) to write a blog (4) about Minelab FSB metal detectors (5) on Minelab's own website (6) has no idea what he is talking about.


Hmmm....
 

Chris(SoCenWI)

Well-known member
AVXVA,

I'm sticking to my guns. I watched the video IDXMonster posted, and read Gordon's article. In the video the guy goes through the noise cancel channels with a frequency meter next to the coil. It goes from 16.2 kHz on channel 1 to 12.6 kHz on channel 11. That is a piddling total change of 3.6 kHz over the 11 channels, which means it lowers the frequency on one of the square waves by .33 kHz each channel switch. FBS technology uses two square wave pulses; the one changed by noise cancel and another that remains constant to generate 28 different receive frequencies between 1.5 kHz and 100 kHz.

If you are trying to tweak a detector to have a better response to a certain type of target you need to change the frequency by a lot. Perhaps on a single frequency detector going from 7 kHz to 20 kHz would make a noticeable difference. But on the FBS detectors you are already checking on 28 frequencies spread from 1.5 kHz to 100 kHz, so the 7 and 20 kHz frequencies are already covered in this range, plus many others. Noise cancel just slightly shifts the value of all the receive values in the hopes of getting away from local EMI. Gordon says as much in his article. If someone sees a better response on some channels when manually shifting channels most likely means the poorer performing channels probably are suffering worse from EMI than some of the others.

I've never found the noise cancel makes much of a difference around power line EMI. I always run manual sensitivity, sometimes after a noise cancel I can bump the sensitivity by a notch or two.

Next time you fire up a FBS detector hold the coil next to your headphones and hit noise cancel, you can hear the machine dropping the frequency.
 

AVXVA

Member
Hey Chris,

Well done. I respect your answer. (I agree with attitude of a professor I once had, "I don't care what the answer is, I just want the correct answer.")

Give me your ideas on making the Etrac as deep as possible.

Thanks!
 

Chris(SoCenWI)

Well-known member
AVXVA,

Not much you can do to improve depth, all the FBS detectors work pretty good right out of the box. Probably the biggest thing is sensitivity; in Auto modes the detector tends to drop the level considerably in high trash/EMI settings. I always run manual until it starts to get twitchy. The bigger question than depth is finding coins in trashy ground.

Chris
 
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