Centre tapped or bifilar mono coil.

[Ferric Toes]

Has anyone tried this arrangement?

A centre tapped 1200uH coil will have 300uH from one end to the tap. This is a good inductance for the TX, which is connected to the tap. The RX is connected across the whole coil for more signal gain. This idea was mentioned somewhere a few years ago and it seemed to be a good idea, but I have heard nothing since.

Eric.

[Skippy]

Presumably it doesn't have to be centre tapped, any realistic transformer ratio is viable? Eg. if you wound it quadrifilar and wired it up as a 4:1 ratio, would that do what you were thinking of?
Funnily enough, when I saw plans/instructions for making the flat spiral PI coil out of figure-8 loudspeaker wire, I wondered if using the two wires seperately would offer any benefit.

[Carl-NC]

Yes, years ago I did simulations on that and even built one. It was at White's and I don't have those notes any more, but my recollection is that it worked but it must not have provided a big advantage because I didn't stick with it. I was doing a lot of other experiments at the time, and perhaps that's when I decided to switch over to an h-bridge drive for bipolar TX.

[Carl-NC]

Presumably it doesn't have to be centre tapped, any realistic transformer ratio is viable? Eg. if you wound it quadrifilar and wired it up as a 4:1 ratio, would that do what you were thinking of?

Center-tapped would give a perfect differential response that could be used to drive a differential preamp. Also, I suspect there's a limit to how much winding you can put in the thing, at some point inter-winding capacitance will make it sing.

[green]

http://www.geotech1.com/forums/showt...002#post199002

I tried the center tapped coil awhile back, above thread. Don't know what to expect. Looks like it slows the decay a lot. What benefits should I expect other than maybe doubling the receive signal?

[Carl-NC]

I threw together a Spice sim over the weekend, it jogged my memory a bit. I think I ended up with a total of 300uH, or 75-CT-75. If I do 300-CT-300 there's too much parasitics and it rings. I do know I built this once and it worked just fine, but I think it didn't offer much advantage overall. I also made it differential by driving each half, thereby making it a bipolar TX, but I went with the H-bridge design as it gave me more flexibility in what I was trying to accomplish.