figure8 Rx

[green]

I've been using a figure8 Rx with a oval Tx over Rx. Wondering if two round Tx coils connected in series, one over each Rx coil would be better than the oval Tx. Anyone tried it or have a guess if it might be better?

[WM6]

Is it optical view only or RX coils are not the same in real?

[green]

Is it optical view only or RX coils are not the same in real?

It's a picture of the 8inch test coil I'm using before potting in foam and shielding with graphite paint. Rx coils connected in series and opposite phase to reduce ground signal and external noise.

Rx coils wound the same, outer windings connected together. inside windings connected to a differential amplifier

[Skippy]

I'm confused. This is where a picture is worth 1000 words. Show us a drawing, detailing how the two TX coils are wound , ie. current flow / phasing.
In my head, it sounds like a bad idea, some of the magnetic field will be cancelled out by wires close by travelling in opposite directions ?

[EL NINO]

Mr. Green ... According to me, one oval Tx winding is better .. and according to me it gives a more even Tx field in coplanar design ..,
two circuit Tx windings according to me I will be more complicated to accurately balance .. and the next question is whether or not there will be in the middle of the coil weakened TX field....

"8" coil ... reminds me very much of SuperD coil but in another function coil detection orientation also design coil...

But it's an interesting idea, even the experiment itself..

[Carl-NC]

Wondering if two round Tx coils connected in series, one over each Rx coil would be better than the oval Tx. Anyone tried it or have a guess if it might be better?

It might improve the sensitivity in/near the center part of the coil. You should give it a try.

[green]

I'm confused. This is where a picture is worth 1000 words. Show us a drawing, detailing how the two TX coils are wound , ie. current flow / phasing.
In my head, it sounds like a bad idea, some of the magnetic field will be cancelled out by wires close by travelling in opposite directions ?

Not having much luck drawing the coil. Another attempt at describing the coil. The coils are spiral wound. Winding starts inner diameter winding CW. The two receive coils are positioned next to each other not flipped. Coils in series with outside windings connected causing the phase reversal. Inside windings to amplifier. Should be the same as twisting a mono coil into a figure8. Same problem with null at coil crossover.

The idea came from ITMD page 58, Figure-8 coils. Wanted to try a couple things. Look at signal when Tx on to determine ferrous or nonferrous. Try a differential amplifier with Rx connected to amplifier without any input resistors to eliminate resistor noise. Plus the benefits of noise reduction.

I get better S/N with this coil compared to a mono coil when recording target decay. Have wondered if using two round coils in series for Tx would be better. They would have to be connected in phase for minimum Rx signal when Tx on.

I have started making one to try. I have four 8 inch round coils already. Some problems will be higher inductance and resistance compared to the oval Tx. Don't know if null at crossover will be worse.

[Orbit]

Is this how it is ?

[Skippy]

Is this the equivalent of how the TX is behaving? There seems little point in having the sharp V 's in the shape... maybe some 'hourglass' necking of the basic oval would have some merit, but how it could be made in practice I don't know ...

[green]

A drawing. Tried grounding center tap, think works better not grounded.

Tx with two round coils would be wired with the outside of L3 to inside of L4, no phase reversal. Tx3(inside of L3) Tx4(outside of L4)

[green]

Been trying to guess if two round Tx coils would be better than one oval Tx coil. Was think Rx signal wouldn't be effected, Tx field only but then wondered if there is coupling between Tx and Rx coils when Tx off. If yes then one side should have a higher Rx signal than the other? The coupling would effect noise cancelling also. Maybe someone who understands coupling could reply.

[green]

Been trying to guess if two round Tx coils would be better than one oval Tx coil. Was think Rx signal wouldn't be effected, Tx field only but then wondered if there is coupling between Tx and Rx coils when Tx off. If yes then one side should have a higher Rx signal than the other? The coupling would effect noise cancelling also. Maybe someone who understands coupling could reply.

Tried some tests to see if I could understand effects of coupling without much success. Tried a test to measure Tx strength with the (2) round coil Tx, connected in series same phase and opposite phase(same as twisted mono ?) and a oval same size as the (2) round coils. Wound a pickup coil and measured signal strength(mV) at different positions and distances. Don't see why the oval isn't just as good as the (2) round coil Tx. Probably have to finish the (2) round coil Tx with (2) round coil Rx and compare with the oval Tx in case I'm missing something. Maybe coupling effects?

[green]

The second set of data reply #12 should be labeled opposite phase. Same as twisted mono.

[6666]

Probably have to finish the (2) round coil Tx with (2) round coil Rx

Interesting experiment, if possible could we get a picture please so we can see what you are doing thanks.

[green]

Interesting experiment, if possible could we get a picture please so we can see what you are doing thanks.

Some pictures. Coils taped to pieces cut from Elmer's foam board(5mm thick). Pickup coil slides on wood dowel marked at 1inch increments.

Tested a single 8inch coil. At 2, 4 and 6inches about 2 times the signal, double coil same polarity. Close to the same signal at 12inch distance.