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Originally posted by ivconic
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What you have to say regarding the coil parameters? Any advice?
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What you have to say regarding the coil parameters? Any advice? -
change sound part on this
its more right.Comment
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I never really measured coil.Originally posted by dbanner View Post
I guess it is common White's coil from that series (5000, 6000 etc).
6.5-7kHz i guess.Comment
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Originally posted by ivconic View Post
One lunatic man at whites did make this rat nest layout for sure, another lunatic man (Ivica) has traced over layout both sides!!
That is no easy task!
I am tempted to send it off to china pcb. That would be third lunatic action.
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Originally posted by dbanner View PostOne lunatic man at whites did make this rat nest layout for sure, another lunatic man (Ivica) has traced over layout both sides!!
That is no easy task!
I am tempted to send it off to china pcb. That would be third lunatic action.
Oh... that's one of the easiest among numerous that i did so far.
I did that long time ago. Recently i just added values and designators.
Also i corrected the trace where "Sensitivity" pot is about to be connected.
On original pcb it was complete printed trace and later cut (!? they did it like that in White's) and two simple wires connected to Sense pot.
Original pcb design is too large, as far as i am concerned.
Since it is indeed simple design; it would be good to be put on much smaller 2-layer pcb, in order later to be packed in very small enclosure.
Even better if done in SMD.
I am having here brand new, never used; 6.5kHz (internal cap in coil) 25cm concentric coplanar coil for Bounty Hunter.
I wonder if it will suit 3900 detector?Comment
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Originally posted by ivconic View Post
If I'm not mistaken, the Rx L of the BH coil is 2.6mH or thereabouts.
And I'm not sure of any tuning caps internally, also the Q of the coil makes some difference in matching the bandwidth of the front end. So the inductance and R matters.
I'm not an expert. But I suspect it will work poorly.Comment
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Probably.Comment
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I have tried to find more information on the 3900D. Seems it came with a 6B coil for sure.
The Tx coil has to be tuned to 6.59kHz. In the 6B coil, this is achieved through the use of internal caps in the coil housing, that's fine.
But I could find no evidence of any tuning caps inside the coil for the Rx coil. All the original schematics for the detectors which came with the 6B coil show only a 1nF capacitor (located on PCB) in parallel with the Rx coil, whereas the internal Tx caps are shown within the coil housing.
I am left to conclude that the 6B Rx coil is tuned to a whopping 39.5kHz!!! (Tx-16mH and 1nF capacitor in parallel).
I have no idea what the phase shift at Tx/ Rx coil nulling would be. ( maybe it will end up being in phase) ie 0 deg phase shift.
Now the Rx coil and preamp will still output 6.59kHz signal, no problem.
But this was entirely unexpected.
In previous posts I suggested to try tuning the Rx coil to 4.68kHz, similar to IDX, but this is quite wrong!!!!Comment
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All this leads me to believe perhaps a Rx coil with much lower inductance (say between 2mH and 5mH), if tuned to 6.59kHz, maybe could work just fine. This would make winding a DD coil a simple task.
I'll soon find out when I finish construction of the circuit.Comment
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Carl's coils' data. so you can believe.
White's
Name TX-L TX-R (ohms) TX-fo TX wire RX-L RX-R (ohms) RX-fo RX wire
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6B 4" 1.74mH 7.71 --- --- 19.7mH 35.1 --- ---
6B 8" 1.72mH 6.47 --- --- 12.92mH 32.2 --- ---
6B 10" 1.69mH 6.68 --- --- 16.2mH 39.1 --- ---
6B 15" 1.59mH 6.36 --- --- 21.0mH 51.5 --- ---
Spectrum 9.5" 540uH 1.40 --- --- 36mH 122.8 --- ---
DFX 9.5" 540uH 2.67 --- --- 13.79mH 35.8 --- ---
Eclipse 5.3" 554uH 2.76 --- --- 14.01mH 31.1 --- ---
Eclipse 6x10 678uH 3.51 --- --- 14.19mH 54.6 --- ---
Bigfoot (XLT) 554uH 1.81 --- --- 43.0mH 146.7 --- ---
i think 32... 39Ohm value for RX says there is serial resistor 22...24Ohm.Comment
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The 3900 came with an 8 inch 6B coil, so 12.92mH with 1nF cap works out to 44.3kHz Rx resonance. So that's what I'll be using. Thanks for posting.Comment
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Sprint layoutComment
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I find it hard to believe that Rx resonance in the 6B coil is so high. Whites uses lower frequency for Rx tank circuit than Tx resonance. I have found that 0.75*Tx is typical for the Rx resonance in the old whites detectors.
But I searched high and low and cannot find any evidence of internal capacitors on the Rx tank for the 6B coil. All inspection of the PCB's for the classics and the 3900 show only 1nF cap across the R coil.
So I am left to do "trial and error" testing.Comment
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But then here is a quote from Carl Take from here:https://www.geotech1.com/forums/show...nding-RX-value
"There are 2 reasons for not resonating the RX coil at the TX frequency. First is that the phase response is very non-linear at resonance, making target ID more difficult. Second is that at resonance slight variations in L or C make a big difference in response. So most manufacturers resonate the RX off of the TX frequency, usually higher, usually 2x to 5x."
END QUOTE
What the hell??? Two to five times higher??
Maybe it is typo error???
If this statement is true( for some coils arrangements, not all, obviously) then maybe the 6B coil is one such coil??
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