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Next step is to get to work on the coil design. The original is concentric coplanar type, I'm not certain. But a DD coil could be a trickier matter with those feedback pots. Best to try to replicate the original coil first, later on experiments can be made with other coil arrangements.
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dbanner,Originally posted by dbanner View Post
if original coil is concentric coplanar type, a nulling will be needed, I suppose, like a normal coil for IB detector. Do you plan to use this approach?Comment
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I'm a bit rusty on the matter.
But I think I recall it being a concentric type coil, but who knows. The Nautilus dmc2 uses a concentric type with identical tx/rx circuit and feedback pots.
If you notice the schematic for the aquasound, the coil is depicted with 40-10-ct-10-40.
Those 10-10 windings I suspect are the feedback coils, which null the RX in a concentric coplanar type coil.(yes, with a centre tap tx, the buck is also centre tap)
So a DD coil only requires 50-ct-50.
The pot connections taken from either side of the coil ends.
This is my thinking.Comment
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nautilus coilComment
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dbanner,
buck coils must wounded in opposite way respect to TX coil so, if 10-10 windings are for bucking, the total inductance of 40-10-ct-10-40 should be less then 50-ct-50 of a corrisponding DD coil.
Kt315,
thank you for share photos.
From photos I note some different components values regarding preamp between Nautilus and Aquasound schematic.Comment
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Although the mutual inductance is opposing, I expect that the effect is small, 50x50 turns will get you roughly a little more inductance than 40-10-10-40 buck coil arrangement.
But this is inconsequential, as the RX coil must still be balanced close to full resonance. Don't matter if the TX frequency is 51kHz or 49 kHz. You can tweak the tuning cap value to resonate the coil to 50kHz if that is your goal.Comment
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After watch Nautilus coil Photos, I have marked the wirings inside coil. For shure the two 10 ct 10 windings are bucks. See my attached draw.
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Something still looks wrong. For example, if you follow the foil trace on the small PCB, then it seems that buck minus(-) is connected to one end of the RX coil. This cannot be right.
With the exception of the feedback pots, the buck coils and RX are electrically isolated from one another.Comment
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I think I've got it right now. Please follow me.
The red and green wires you labeled as buck minus (-) and buck+, is actually the buck coils ground wires. They are connected to same spot on PCB.
The two ends of the buck coils are connected to the two TX ends in a place not visible from the photo.
You see, we are dealing with a bifilar coil!
Hence the green an red wires, look at the tx wires, green and red, which means two separate windings. Now where are the other ends of those tx windings?
Ah dr.watson.....they are connected to the two ends of the buck coils( a green and a red, hidden from view. Case closed.
A bifilar coil.
The trace out from the guy who opened the coil was improperly done, I don't think he fathomed such a coil. Hence the confusion.Comment
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Yes, you rigth.Originally posted by dbanner View Post
Seems me the coil is wired differently to Aquasound schematic.
Anyway is clear for me that the two 10 ct 10 windings are bucks.
I have modified the picture.
No, are "GND Buck+" and "GND Buck -" that are soldered to the same GND spot. This is correct. The another wire is green and more thick respect to RX wire; it could be for connect the shield.Originally posted by dbanner View PostComment
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Altair, looking again at your drawing, you are correct. So you figured it out it's a bifilar coil.Comment
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