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Results 1861 - 1890 of 1917
I'll have a go at one reason:
The ability of a detector to find a deep target is limited by the problem of distinguishing the weak target signal from the ground signal. A lower detector frequency produces less ground signal, hence a smaller/deeper target can be distinguished. But the target needs to give a decent response at the low frequency. You won't find many gold rings with a 1 K
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Pimento
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Thomas Dankowski Metal Detecting Forum
Dew. Yes, I didn't mention it because I incorrectly thought it was CZ-like, transmitting both and receiving/interpreting both together. I hadn't realised it could selectively respond to either freq or both (correlate mode). It's design is still compromised by transmitting both at once, I suspect. Doing only one at a time, in the traditional tuned-circuit way, must be slightly bett
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Pimento
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Thomas Dankowski Metal Detecting Forum
Digger - They're different internally. The receive coil is identical, I think, but the transmit coil is unconventional on the T2, and appears to be centre-tapped. This need for a centre-tapping is why you can't get concentric's for the T2. A conventional concentric coil, with the small bucking-coil next to the receive coil is not really viable with a centre-tap. The electrostatic
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Pimento
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Thomas Dankowski Metal Detecting Forum
'She' has a facebook page, username of 'hotmarytran', and the site she is affiliated to is www(dot)usedmetaldetectorsforsale(dot)com, which looks to be translated from Martian. This info comes from Garrett's facebook page, via Google.
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Pimento
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Thomas Dankowski Metal Detecting Forum
I imagine he's a Far East based retailer, doing market research on what brands are liked etc. But posing as a 21 year old girl from Texas and asking 'What should I buy to find Hidden Treasure' is not genuine.
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Pimento
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Thomas Dankowski Metal Detecting Forum
Google his username. He's joined every MD forum in the English-speaking world in the past week, with an identical intro-line. And he's had his account deleted from most of them already.
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Pimento
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Thomas Dankowski Metal Detecting Forum
Guys - it's a spammer. Seen him on another forum, he has links to a detector sales website.
I reported the original post, but there doesn't seem to be any moderator.
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Pimento
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Thomas Dankowski Metal Detecting Forum
If you're after 'deep silver in hunted-out parks' you're looking for coins with approx. natural frequencies from 1KHz (dollar) to 4KHz (half-dime). The optimum single frequency for this would be 4 - 6 KHz, so basically CZ frequency. A new CZ would definitely sell (in the US), and it would have all the usual characteristics of the modern First Texas machines, light, long batter
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Pimento
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Thomas Dankowski Metal Detecting Forum
I think you will find the F75 is designed in every way to be a single-frequency machine. It cannot readily be 'turned into' a dual-freq machine, though no doubt a lot of the know-how could be transferred to a new-design dual-freq detector.
What sort of dual freq machine did you have in mind? Something switchable between two different freq, like an XP deus? 'Two complete detectors
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Pimento
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Thomas Dankowski Metal Detecting Forum
You're not discriminating out iron, you're discriminating out things that target ID below 22. If a lump of iron, or coke, or anything else, causes a false high-90's ID, it won't be discriminated out.
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Pimento
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Thomas Dankowski Metal Detecting Forum
Disc settings don't do 'Power Boost' (transmit power is constant) but they do affect overall sensitivity. There is no 'switchover' at 5 and 19 (or whatever), it's a gradual drop in sensitivity from Disc = 0 through to Disc = 12 (approx), returning to near-full sensitivity at disc = 24 (approx). An air-test shows the drop clearly, in-ground it's harder to get the
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Pimento
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Thomas Dankowski Metal Detecting Forum
The coils aren't compatible. When Fisher re-engineered the T2, they changed the transmit-coil parameters and the drive electronics so that both concentric and DD coils would work.
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Pimento
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Thomas Dankowski Metal Detecting Forum
They could get a little lighter. Electronic circuitry will consume less power, meaning lower battery capacity is needed, and the reduced cost of lightweight high energy-density lithium-ion / lithium-polymer cells would combine to knock off 100 grams (a quarter of a pound, the weight of 4 x AA cells). Coils and shafts are unlikely to get much lighter.
Wireless headphones (in addition to wired)
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Pimento
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Thomas Dankowski Metal Detecting Forum
Dew. It is possible to assemble something cheap out of stuff you could get cheap/free. One useful part you should be able to obtain is a laptop power supply. These are commonly 16 to 20 volt output, with a hefty current available, often 3+ Amps. This could be used to make a 'brisk' charger. Trying to make a really rapid charger is just making things expensive - high currents, the need f
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Pimento
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Thomas Dankowski Metal Detecting Forum
I'm slightly confused. Dew, I thought you "would love a car charger", and you had a home trickle charger (the 60 mA one). As it's a trickle charger, you can't really over-charge the battery with it. So if you're unsure whether a battery is flat, part-flat or whatever, just put it on charge beforehand for 10 hours. No harm will come.
One possible issue you may have i
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Pimento
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Thomas Dankowski Metal Detecting Forum
Sorry to disappoint you, coinseeker, but your 'rule of thumb' is not correct. Coils are perfectly capable of detecting objects further than their diameter away, also, depth roughly varies with the square root of the coil diameter (airtest), so expect the 5 inch coil to give approx 70% of the 11 inch's depth.
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Pimento
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Thomas Dankowski Metal Detecting Forum
There are several strategies used to charge NiMH batteries, but the most common is to limit the current, and allow the battery voltage to settle at its own level. To trickle-charge, this is all you need to do, choosing the current such that a full charge takes typically 12 hours. This is sufficiently slow that overcharging causes very little harm. Quick- charging (5 hours or less) needs some cont
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Pimento
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Thomas Dankowski Metal Detecting Forum
The reason given as to why NiMH cells should not be used in the dry cell pack is correct. The small difference (1.25V vs. 1.5V) adds up when there is 8 (?) cells in series. The proper sealed Nicad/NiMH packs will have 1 extra cell in them to give the correct voltage. It's a similar thing to those PP3 9-Volt block batteries - crack open an alkaline one, there's 6 cells in series, open a
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Pimento
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Thomas Dankowski Metal Detecting Forum
I know nothing about the excalibur's battery pack construction, but it appears it can be dismantled in some way to allow replacement of the cells. A manufacturer of aftermarket battery packs here in the UK, Strikalite, list two packs as suitable. The NiMH is much higher capacity, I imagine it would probably take 2 days to fully charge using the existing (trickle?) charger, but would give muc
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Pimento
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Thomas Dankowski Metal Detecting Forum
Coil resistances are not what is limiting detector performance. If the lower resistance of silver was beneficial, it would be simpler to use a slightly thicker gauge of copper wire, or two (or more) strands in parallel.
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Pimento
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Thomas Dankowski Metal Detecting Forum
Give the small circuit board a brush to remove any salt crystals/debris. Everything else looks sealed up. If it still works OK on the GB, seal it up. If you use silicone sealant, I would advise using 'Low-Odor' types, which don't give off acetic acid (vinegar) fumes when curing. These could potentially cause corrosion on the circuit board.
If you're curious, the small loop of
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Pimento
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Thomas Dankowski Metal Detecting Forum
Very interesting, and surprising, too. You would have thought they would choose the existing coil nearest in frequency, ie. the 13Khz F75 unit.
Looking again at the recent Ivanll post, it seems the GB coil he has is very close to the 'mystery' coil in spec's. I assumed Ivanll had tried the coil and found it didn't work, maybe I'm wrong and he didn't want to risk i
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Pimento
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Thomas Dankowski Metal Detecting Forum
I think one of the least critical parameters of a coil is the receive coil resistance, so engineering convenience might result in the difference between your two GB coils.
As well as having the correct inductance and resistance, the other critical parameter is the null (induction balance) of the coil. This is frequency-critical, and operating a coil at a different frequency to that intended will
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Pimento
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Thomas Dankowski Metal Detecting Forum
Ivanll.
That's interesting. It's not a T2 coil (pin 5 is connected to 3,4 on that) and it doesn't match the resistance measurements of either of the F75's 5DD or 11x7DD coils (pin1-2=36 Ohms, pin3-4=2 Ohms). I would have expected the GBpro to have closely-matched 5 inch and 11x7 specifications, and your 11x7 has higher transmit-coil (3 Ohms) and receive-coil resistance (57 O
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Pimento
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Thomas Dankowski Metal Detecting Forum
Measurement of resistance and possibly inductance on the appropriate pins could distinguish T2, F75 and 'other' models. Do you have a multimeter?
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Thomas Dankowski Metal Detecting Forum
It wouldn't surprise me if microprocessor-based detectors include a small amount of hysteresis in their operation ( the equivalent of play/backlash in a mechanical system). For example an internal signal level of 1.00 Volts may be needed to trigger a 'target detected' mode of operation, and a drop below 0.90 Volts would be needed to define the end of a signal. This way, marginal si
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Pimento
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Thomas Dankowski Metal Detecting Forum
That looks like the George Payne article quoted there. That describes how Discovery machines TID, one of the many different ways.
The actual 'single-figure' ID that detectors would give if they were laboratory instruments would be the phase lag in degrees. This varies from Zero through to -180 degrees. Near-zero would be the ground itself, -90 would be a low conductivity non-ferrous ta
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Pimento
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Thomas Dankowski Metal Detecting Forum
One technical point: Sonar is sound, not radio.
And a question: What limits the depth of your current machine, the ultimate (airtest) depth, or lack of good accurate target ID? If it's TID related, then your saltwater/sand combination is the real limit. You may be able to squeeze another few % depth out with circuit changes, basically tailoring your machine to your specific conditions.
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Pimento
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Thomas Dankowski Metal Detecting Forum