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FBS

N

Neugene

New member
I posted this in the Explorer forum but got no responses, so I hope that posting it here as well is not a breech of etiquette.

I understand that the Explorer transmits 28 frequencies at the same time. It even says so on the spec sheet. However, I have never seen any specs on how many frequencies the receive circuit receives at one time. Any ideas?

I own an SE so I am not trying to bash the machine but I have heard that it only receives on two frequencies similar to the DFX. You "hear" a lot of things when researching on the net and I would just like to get the facts straight.
 
My "idea" --not an answer based on knowledge--is that if all frequencies were transmitted and received, noise cancelling would not stop interference when 2 Explorers were operating next to each other.

Also manually selecting a channal would not be possible if all channals were receiving simultaneously.
 
it transmits the 28 freq. then it figures the two best calculations in it's computer and reports them to screen? So if that's true it must use them...but I'd still like to hear it from one who knows and understands?

KCK
 
Sandy from Minelab emailed me stating that it transmits and receives 28 frequencies simultaneously. I then replied to her message asking how many of the 28 received frequencies were actually processed and interpreted for target information. I have not heard anything back yet but I will keep you posted.
HH
 
As does my car which takes me to hunt and don't know beans how a car works either..For those really interested call Sandy or speak to one of the minelab tech's for a technical interpetation..
 
The Explorers are "time domain" detectors. The transmitted signal is a series of bi-polar rectangular pulses.

* The period of the pulses determines the minimum frequency.

* The harmonics of the fundamental determine the number of frequencies

* The rise and fall times (of the leading and trailing edges) are controlled to limit the maximum frequency.

The signal of the receiver coil is examined in the time domain to characterize the target.

Note that this process is completely different than single frequency or pulse induction detectors.

Hope this helps.
HH,
Glenn
 
Noise cancelling does work when one Explorer operating next to another Explorer. Noise cancelling is accomplished by changing the transmitted fundamental frequency on your detector to be slightly different from that of the interfering Explorer.

The received signal is analyzed by comparing the received signal against the transmitted signal (synchronous demodulation). If two Explorers are operating at different fundamental frequencies, then the effects of an interfering Explorer are essentially cancelled out. The degree of rejection will depend upon difference between the fundamental frequency of your detector and that of the interfering fundamental frequency.

HH,
Glenn
 
Thanks for the info. I think I have a feeble understanding of what you are saying but can you "dumb it down" a little? My forte is mechanical design, my electronic engineering skills are more than a little rusty.
 
Glen: If I understand what you are saying then counting each harmonic as a different frequency then the detector would not have just 28 frequencies but counting the harmonics the number would be endless.
 
Thanks Glenn, guess I need to see an oscillogram to memorize this. But I do understand your explanation :thumbup:
What I don't understand is - how "noise channel" ("cancel") works. Can you explain that, please?

[size=large]update: Oops, missed your post below. Wow, that explains it all!
Thank you very much and HH![/size]
 
Glenn,
This is my simplified understanding of your answer. Please let me know if I am in the ballpark.

The Explorer transmits a square wave containing a base frequency and N number of harmonics. Then it samples the return and performs an FFT from which you get X number of frequency readings. The expected frequency response is compared to the actual frequency response in order to locate a target.
My question is does X=28?
Is all the data from X taken into consideration when presenting results to the user?
 
Neugene,

The Explorer transmits a square wave containing a base frequency and N number of harmonics.
This part of your understanding is correct.

Then it samples the return and performs an FFT from which you get X number of frequency readings. The expected frequency response is compared to the actual frequency response in order to locate a target.
This part of your understanding needs clarification. The analysis of the receiver coil signal is done by examining the wave shape in the time domain (i.e. what does it look like on an oscilloscope?). It is my understanding that this is done by examining the rise time and the nature of the signal decay. There is no examination of frequency components in the frequency domain (e.g. by using the fast Fourier transformation [FFT]).

You can go on-line and examine the patent #5,537,041. This gives a good set of waveforms that will answer many of your questions.

I hope this is of some help to you.

HH,
Glenn
 
I believe that you are correct in your statement. In general any repetitive signal (with discontinuities) has an infinite number of harmonics. The magnitude of those harmonics depends upon the shape of the waveform. For example, a square wave has only odd harmonics that fall off as 1/n (where n is the harmonic). Therefore, the 28th harmonic is only 1/28 the magnitude of the fundamental.

By controlling the rise and fall time of the transmitted square wave one can greatly reduce the magnitude of the harmonics beyond the 28th.

Hope that answers your questions>

HH,
Glenn
 
I wasn't able to understand very much of the link but one thing I do know is that the Explorer works very well in the ground I detect, with excellent tone and meter ID like nothing else I've tried. Got to admit, I haven't tried them all but enough to realize that it works well for me and better than any single freq. unit can for general purpose detecting. I know there are several single frq. new kids on the block that I have not tried but all one has to do is read between the lines and watch who sells them after a short time to know that there are limitations to what they can do, maybe they are good for specialty uses but who wants to spend that kind of money on something that is relegated to limited use?
I can take the Explorer to any site and detect and have great results, that is something I don't see from some of the newer ones.
Some use no disc. with the Exp while others use a lot of disc., both with very good results. With some of the new ones, to get the best results, one has to sure to set it up just right, that's not how the Exp. is, and it does not like iron bottle caps, pieces of iron cans and various size iron scrap pieces, say try out the others and see how they do on that junk.
I do have some single frq detectors to play around with and have used some that later I sold but when I want to detect, the Explorer is first one I choose to use.
Ok, if you have one of the newer detectors, don't get offended by this but this is the way I see it:lol:
 
Steve,

I presently have two single frequency detectors (XLT and Teknetics T2) to go along with a PI and Explorer II. The T2 has some good features such as very light, great recovery speed and extremely long battery life. The T2 has real problems with crown caps which I find very annoying.

The Explorer is my "go to" detector.

HH,
Glenn
 
Wonder where the fundamental frq is centered and what would happen if it was either lowered or elevated and if another detector could be made that would be more sensitive to low conductors. I take by what has been said so far that the other 27 frqs are harmonics or am I missing something...
Say maybe the next Explorer could have interchangeable coils to match it's output. I am guessing the Explorer freq is setup to where it is hotter on higher conductors and if the fundamental frq was optimized for low conductors, it would loose some of its ability to ID trash and/or be more noisier, just like the single high frq detectors do?
 
Steve,

Yes, there is a fundamental and 27 odd harmonics.

The fundamental is nominaly 1.5KHz.
The 4.5KHz component is 1/3 the magnitude of the fundamental.
The 7.5KHz component is 1/5 the magnitude of the fundamental.
Most of the signal strength is found in the fundamental and 3rd harmonic. The is about where most VLF detectors operate to maximize the response to low conductive targets.

It is my suspicion that generally a low single frequency VLF detector will be more sensitive to low conductive targets than the Explorer. This is especially true to small gold nuggets and gold chains. But, I may be exposing my ignorance with this statement.

HH,
Glenn
 
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