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Chet

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Chet last won the day on June 23

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  1. I think it is a quality control problem in the soldering or internal board connections. The more we gently rapped on it or set it down quickly changed the intermittent nature of the problem. But we could not get it improve or to stay broken.
  2. Jason that is the same problem that a friend had. Last year three of us with GPX 6000’s met up for a week of detecting in the Eugene’s off of Jungo Rd. His detector was new out of the box. It would work and then go crazy just like your detector does. We tried different coils and batteries from the other two detectors. Each combination would work then go crazy again. Since I had my GPZ 7000 as a backup I used it and let him use my 6000 for the week. Minelab replaced his detector and the new one works fine. It’s time to send yours in for a new one. Chet
  3. I have used the GPZ 7000 GPS for 6 years and really appreciate having it built in to the detector. Prior to the GPZ 7000 when in the wooded mountains and canyons I always carried a hand held GPS. After I started detecting with the GPZ 7000 I always Set a Waypoint and Start a Track as I left my Jeep. And entered a Find Point for each nugget found. I quit carrying the hand held GPS since the GPZ 7000 was easier and faster to use. Now with the GPX 6000 I carry my phone loaded with a map application, GAIA GPS. I have loaded it with most of the GPZ 7000 Way Points and Find Points.
  4. I just ran an indoor test of my GPX 6000. Using the supplied Bluetooth connected headphones with max volume. With room lights including one fluorescent light ON and nearby computer ON the EMI noise with the 11” Mono coil is almost unusable at any settings. With the 14” Double D coil; Max Sensitivity without Threshold ON it is almost silent; With Threshold ON it has a normal level of EMI noise (similar to the 11” Mono EMI level in open country). It detected a sub-gram nugget a few inches from the coil with no problem. My Galaxy A10e phone which I carry with me when detecting (Turned ON) causes no problems when rubbed against the Control Head or the Detector Housing. It is detected as a target when moved over the coil. It appears that the electronics shielding in my GPX 6000 and the 14” coil cable are working quite well. Have a good day, Chet
  5. Most EMI is picked up by the coil. The coil receives EMI similar to the antenna of an AM radio. The larger the coil surface the more EMI is detected. Proper EMI shielding of the coil is the most critical factor. For a low impedance mono coil the approximate three foot of lead can be a twisted pair of unshielded wires and be very effective in canceling EMI. It does this by the EMI on each wire being balanced and of opposite voltages being introduced by the twisted wires receiving equal and opposing EMI signals. With a Double D coil the low impedance transmit wires are often a unshielded twisted pair. The higher impedance sensitive receive coil is normally connected by a small diameter shielded cable.
  6. The shielding quality and effectiveness of different coil manufactures could explain some of the differences in EMI levels from different coils. Shielding must provide a critical balance between EMI, Ground effects and best overall detector performance. Most coils are shielded with a conductive paint which varies in resistance by design and by quality control. Too low of a resistance paint applied incorrectly will reduce EMI as well as Detector performance. Too high of a resistance paint will allow more EMI in and more ground noise. Shielding method and materials used in the approximately three feet of transmit and receive leads is also important to preventing EMI problems. Some coils may have quality control problems during the manufacturing process. As with many products performance reports from the users generally sorts out the better products. Have a good day, Chet
  7. Shortly after I got my GPZ 7000 I tested the WM12 delay and found it to be approximately 20ms which is close to the Garrett Axiom Z-Lynk 17ms delay. Reference; https://www.detectorprospector.com/forums/topic/2854-testing-the-minelab-pro-sonic-response-time/#comments Have a good day, Chet
  8. “So just having some fairly decent shallow discrimination on a prospecting machine would be pretty useful in many cases and save a lot of time just being able to concentrate on digging the targets that are higher probability of being gold,“ My preference is to incorporate a separate VLF circuit board or integrated VLF circuity within a Pulse Induction detector with a fast switchover from one mode to the other. The switchover could be as simple as turn off/on the appropriate transmitter. The coil would require special or additional winding/s but is doable. The display and control functions would change with the mode change. For years when in trashy areas I have carried a modified VLF detector for discriminating and pinpointing. Currently I prefer the Equinox 800.
  9. First some background on discrimination; VLF discrimination is normally dealing with measuring phase shift referenced between a transmitted sine wave and a relatively strong sine wave caused by a target that unbalances a null between the transmitter and receiver coils. This works quite well for small shallow targets that are expected to cause phase shifts within reasonable design limits. The design limits might range from iron nails to large rings or large coins with aluminum, lead and gold in the middle of the range within 12 inches of depth. Also the targets are expected to be within a size range that allows the phase shift to be within limits of the expected possible targets. They do not work well for shallow large targets that exceed the capability of the phase shift measuring circuitry. Nor do they work well for weak deep targets. There are a lot of unknown variables encountered with a Pulse Induction detector to incorporate into the design of discrimination processing. There are so many false variables to deal with unknown target sizes, shapes, wires, rusted metal shapes, and mineralized soil from oxidized metals. Some pulse induction detectors have been built that have some discrimination capabilities. My GPX 5000 with a Double D coil has that capability. It worked on some targets such as nails but overall I found that running the more sensitive Mono coil and digging all targets was faster and produced more gold. I have built a couple of prototype pulse induction discrimination circuits (based on target time constant) which worked on the bench with good solid targets. But failed when junk targets out the ground were tried they failed miserably. Measuring phase shift of the transmitter power waveform similar to what you suggest works well with good targets but falls apart when various questionable or weak targets are tested. A GPZ 7000 or GPX 6000 like detector could be designed from the ground up with a lot of software processing to make some reasonable target evaluations of phase shift and/or target time constant and display a result along with a percentage of probability number. It will take a lot of work and testing with an engineering expenditure to match the task. Hopefully Minelab will find a way to do it. But they may not appreciate the complaints from us users when we are unhappy with some of the limitations.
  10. "a real world square-like waveform that has ringing and finite sloped rise/fall edges due to real world impedance factors" Yes, the amount of ringing and slope of the ringing waveform is shaped by damping resisters (impedance loading). The slope and length of the sloped wave will be altered/strecthed by Eddy Curents emitted from metal targets that were energized by the transmit pulse. Target detection is determined by sampling for changes in the sloped wave with high speed gating/timing circuits of different timings/mode selections. Examples; High Yield timing favoring short Time Constant targets (small nuggets); General timing favoring Long Time Constant targets (large deeper nuggets).
  11. GPZ 7000 ZVT The GPZ 7000 Zero Voltage Transmission (ZVT) technology provides a stable processing period throughout the entire receive period. It also provides a stable magnetic field that reduces the amount of undesirable soil that is detected. This along with better signal processing provides improved detection of small nuggets and larger deeper nuggets. Bipolar (positive and negative) pulses can be generated in standard Pulse Induction detectors. But between pulses the transmit energy starts at zero voltage and builds until it peaks and discharges energy then it must start at zero again in the opposite polarity. This creates current and voltage variations on the power wiring that can adversely affect the receiver and processing circuits. Thus is not as stable as the GPZ 7000. In the attached oscilloscope GPZ 7000 Transmit Waveform displays; the zero volt level is across the vertical center of the display. Both the positive and negative excursions of the waveform pass up and down through the zero voltage level rapidly. In a standard Pulse Induction detector the waveform would stop at zero volts for a short period while the receiver timings and processing completed then start recharging the transmit coil for the next cycle. In the GPZ 7000 the receiver coil timings and signal processing does not require the transmit function to return to zero volts to recharge for a new transmit cycle. In the time stretched displays; the squidgy somewhat sine shaped forms at the top and bottom is time periods where the receiver timings and signal processing can be applied to the receiver coil signals to determine if a target is present. Note; only the Transmit waveform is shown in these displays. The receiver displays are a distorted mess of EMI and ground noise. That is where good engineers really excel in signal processing to extract target information that best fits the Time Constant curves that are displayed in a previous posting. In my opinion reference to the Bipolar power and high voltage pulse with coinciding receive operation as being similar to a VLF detector is not false but somewhat of a stretch. But maybe a good sales pitch. Have a good day, Chet
  12. The GPX 6000 11” and 17” x 13” Mono coils have the same electrical specifications as most previous GPX series coils. That is; the inductance is close to 300 microhenrys (uH) and the direct current resistance is close to 0.3-0.5 ohms. And shielding appears to be similar. The GPX 6000 Double D receiver coil is different from previous GPX series Double D coils. I could not get a DC ohms measurement across the receiver coil. It appears to have a capacitor in series with the winding. Small existing GPX aftermarket coils using some type of adapter/dongle will probably work great. The GPX 6000 works great on small shallow gold by having a fast recovery and processing time for short time constant targets. There may be limitations on large deep gold using large existing aftermarket coils. The GPX may be designed with overall power and sensitivity limited near the GPX 5000 performance. Concentric coils could certainly be developed for the GPX 6000. It would require much development and testing of various sizes to hit sweet spots in performance for different nugget sizes and different depths. Concentric coils for the GPX 6000 will need to demonstrate an overall performance improvement or specific niche in the midst of the other coils to make profitable sales.
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