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Steve Herschbach

Fisher Impulse And The Magic Of A Short Pulse Delay

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55 minutes ago, Mike Hillis said:

You are completely missing the 7ns pulse delay.   That is a huge breakthrough in mass production and target size capability for a pulse unit.

Is it?

https://www.minelab.com/__files/f/254709/KBA 23-1 The SDC 2300 and MPF Technology Explained.pdf

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Do we know what pulse delay some of the timings are running at on the GPX 4500 or 5000? I suspect some are approaching lower delays under 10 but I don't think I've ever read where Minelab has reveled that information. Maybe someone else knows?

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The curve shown in the ML document Steve linked to is not a diagram of target signal decay after pulse switch off, but a curve showing decay of transmit current. It is basically illustrating the effectiveness of the cut off of current which causes the voltage spike - the Pulse.47D878A6-34A4-4C91-9255-244E0FC2C665.jpeg

 

Pulse Delay in PI detectors refers to the delay in microseconds between pulse cut-off and the first sampling of return signals. A completely different thing. Here is a diagram Reg Sniff published many years ago.

The grey line in Reg’s chart is the current output of the detector. The colored lines are return signal from targets and the ground. Pushing the slope of the grey line to the left - a faster delay of transmit current may allow moving the target sample to the left - reducing the pulse delay.

Microsoft’s claim is that the transmit current is gone sooner that some other PI’s - they make no statement as to how much the SDC is able to take advantage of the earlier absence of transmit signal in order to sample target signals earlier. Shortening the pulse delay requires extreme care in circuit design and lay-out as well as very special coil construction.

 

AC865005-DC96-495A-B0E2-6013A047EDC0.jpeg

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On 6/1/2020 at 1:12 PM, Rick Kempf said:

they make no statement as to how much the SDC is able to take advantage of the earlier absence of transmit signal in order to sample target signals earlier. Shortening the pulse delay requires extreme care in circuit design and lay-out as well as very special coil construction.

They do not have to. The SDC 2300 is a machine with a long and very well proven track record.

The SDC runs shorter delays than a GPX under any circumstances and so is the standard to be measured by at this time if pulse delay is the question. Which it is not. The question is real world performance.

I understand what the diagram shows, which is how quickly the transmit current can be shut down... not exactly the same thing that Reg is illustrating. I was referring to the article, not the diagram. I also know what the SDC 2300 can actually do in the real world under genuine conditions. Anyone touting 7uS as something that is a breakthrough is doing so before proving the actual real world capability. It is one thing to air test something. It is another by far to make it work in real mineralized ground rife with hot rocks.

I want Fisher to succeed as much or more than anyone. But ignoring or downplaying the accomplishments of others does not make something better.

The point of the SDC diagram is to show that the transmit current must be dealt with before processing can take place, and that also before a new pulse can initiate, and all this directly impacts the actual pulse delay time. Has Minelab said exactly what the minimum pulse delay time is on the SDC 2300, or has somebody else determined it? Not that I know of. What I do know is the SDC 2300 can repeatedly and reliably find unplanted 0.5 grain gold nuggets in extremely mineralized ground with serious hot rocks involved, and have the ground and rocks be basically invisible. Yes, there is that warble. What of it? The machine performs, and what I am quoting is conservative results. I honestly do not know what the exact lower limit is under real conditions except to say it is under 0.5 grain.

No detector can find gold smaller than saltwater will allow, and it has been made clear already by Alexandre that nobody should expect some kind of magical small gold performance from the AQ. Anyone who knows the limitations inherent in detecting small gold in saltwater will know why this is true. 

Pulse delays, timings, just like frequency discussions, frankly, are just tech talk and spec comparisons that only roughly relate to real world performance. For every plus one thing offers there is a downside, so no one spec is a proven winner under all circumstances. The SDC is not really in the running as a saltwater machine as far as I am concerned for various reasons. The Impulse AQ will easily be the better machine in that environment.

The short delay matters more in the gold prospecting world. And it only matters in so far as it can work while handling both the ground and hot rocks. This is no easy task. It is a function of the ground balance capability, and only indirectly the pulse delay. Since Minelab has a 20 year head start it would be foolish to think even matching a SDC 2300 in real world conditions will be easy. Exceeding what the SDC can do... my bet is on Minelab as much or more than Fisher for that particular task. Time will tell, and only the gold prospecting version of the Impulse can answer the question. The AQ is already out of the running due to its lack of adjustable ground balance control.

Personally, I would be thrilled if Fisher simply matched the SDC for small gold, while getting rid of the warble, and doing it in a lighter machine than the 5.7 lb ergonomic disaster that is the SDC, and for less than $3750. And come on, four C cells - seriously? There is a lot of low hanging fruit there, and splitting hairs over 0.5 grains and 0.4 grains will not be what sells me. Lighter weight, coil options, lower price, and comparable performance. That is a very realistic and a worthy goal. :smile:

Fisher Impulse AU Data & Reviews

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The QED has a pulse delay of 7uS in Mode 1 on the older firmware which was changed to 8 on the newer firmware for those that wanted to update to it, I guess to help with stability but many in hot soils can't run Mode 1, as you go up in the modes the pulse delay goes up in increments up to Mode 10 or mode 15 on the older firmware.

1391785390_delayfigures.thumb.png.6aeaedc9b59b1af7c4709a00428618c3.png

I really look forward to seeing what the Land version of the AQ can do and it's specifications as if it's starting at 7uS it's likely going to be a good detector for my mild soils.

The chart they've done there is wrong as it doesn't mention Mode 11 on the new firmware, Mode 11 is the beach mode which is 7.5uS as confirmed by Howard.  I have the new firmware on mine but I can get away with using beach mode for prospecting.  Beach mode is really just ground balance disabled.

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Phrunt, would you happen to have any #9 birdshot handy? I would like to know if the QED can detect it and how far.

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1 minute ago, Geotech said:

Phrunt, would you happen to have any #9 birdshot handy? I would like to know if the QED can detect it and how far.

I'm no expert on gun stuff, I have some shotgun pellets around I've found gold hunting.  Is this the size you were talking about?

IMG_20200602_151642.jpg.d0bca9fb5e6ef199a9507b7fc0c69726.jpg

IMG_20200602_151828.thumb.jpg.f01e82105db71099f9c309f3b0a82151.jpg

These were just the ones in my finds pouch from my weekend gold hunt with the GPZ.

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0.213g is 3.3 grains, which is #4 birdshot. And that's what it looks like, too. #9 is 0.75 grains which roughly emulates a 0.5 grain gold nugget. I like to use shot because it's consistent, real nuggets are not. If possible, I'd like to send you a few shot sizes to test on the QED. I'm curious about its sensitivity. The next stop for the Impulse train is a nugget hunter and the goal is #9 shot.

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yea, that's no problems.  I could test and do a video.  I don't think people use number 9 here then as I don't recall finding any much smaller than that even with my GM1000.  Great to hear there is work being carried out on the Impulse nugget hunter! Awesome.  I'm highly likely to be getting a AQ Nugget Hunter when the time comes, possibly the beach version too. 

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2 hours ago, Geotech said:

0.213g is 3.3 grains, which is #4 birdshot. And that's what it looks like, too. #9 is 0.75 grains which roughly emulates a 0.5 grain gold nugget. I like to use shot because it's consistent, real nuggets are not. If possible, I'd like to send you a few shot sizes to test on the QED. I'm curious about its sensitivity. The next stop for the Impulse train is a nugget hunter and the goal is #9 shot.

That would be  impressive for a pulse.I  don't think my infinium would hit a lead bb  which  is .18 inches in diameter, and if it did it would be just  barely.

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