DOD coil for TDI

[Geo]

Hi.
I Constructed a DOD coil for my TDI. Concerned how to make its shield. I have two options, one is to wrap with aluminum foil the receiver coils and the other is to place two plywood sprayed with graphite at above and below the coil. What do you think is the best solution ???

[WM6]

Nice idea for your TDI, Geo.

Plywood or hard synthetic foil, sprayed with graphite layer is better solution than Alu foil.

You can assure good wire contact with graphite layer this way (by lead wire through multi hole bored in foil):

[Geo]

Thanks WM6.
I will finish it next week because now i am busy.
I want to construct a coil 50x60 cm so the plywood is the only solution becase there are not coil housings at this dimension

Regards

[WM6]

Not really small coil. Awaiting your report how DOD design perform in TDI case.
Best wishes

[Davor]

By first look I conclude it can not be properly balanced - far too much overlap. It will work for a PI, but the main advantage - balance - will simply not be there.

[Geo]

By first look I conclude it can not be properly balanced - far too much overlap. It will work for a PI, but the main advantage - balance - will simply not be there.

Hi Davor.
I connected the D coils oposite so the result will be zero, but i want to have a small signal after it, this is the reason that it is not balanced good. It is ok for ground rejecting but i have "other" problems. I will open a new post with current problems.


Regards

[Geo]

Grrrrr....


Today afternoon i tried the DOD coil inside the lab and outside it. Problem was the low depth so i will "stay" only at "inside the lab" section.
Main problem is that at Rx coil the wave is not damped. At Tx, wave is ok.
I connected a potentiometer 1K parallel with Rx coil but i can't dampin it.
I attach a photo frrom both waves. Red waveform is the Tx and yellow is the Rx.
Any idea????

[Geo]

I made a carefully null adjusting and now the waveform seems ok. There is an 680R damping resistor (at time of photo).
Problem remains.... not so good depth, at air test the "depth" is about 60% comparing with the 12" original DF coil.
Other ideas????



Here the waveform. Red waveform is the Tx and yellow is the Rx. ..

[WM6]

Geo, seems that TX signal is still oscillating a little and this way coil not sensitive enough:

[kt315]

more damp and more unbalance RX to increase amplitude for. i do not see another way.

[Geo]

Geo, seems that TX signal is still oscillating a little and this way coil not sensitive enough:

Hi WM6. I don't think that this small oscillating makes the coil sensitivity so small. But to be sure today i"ll try to match a beter damping resistor.
Regards

[Geo]

more damp and more unbalance RX to increase amplitude for. i do not see another way.

Or maybe it is a standard problem at "8" coils....., "maybe.."

[Geo]

Geo, seems that TX signal is still oscillating a little and this way coil not sensitive enough:

From the other side, why the Tx signal to decrease the Rx signal????? Here i use seperate coils for Tx and Rx.

[Taktyk]

Show the original signal Tx and Rx - for 12'' coil.

[Geo]

Original 12" coil is mono so for Tx and Rx the waveform is the same.