Possibly modify elliptical coil for CZ ?

[will]

I'd like to put a widescan elliptical coil on my CZ6. Problem is that Fisher doesn't make one. Was thinking about using one from a Garrett Scorpion Goldstinger. Problem is, I don't know the pinouts on either machine. It doesn't necessarily have to be Garrett, as long as it's DD elliptical. Can anyone help me?

[Carl]

Re: Possibly modify elliptical coil for CZ ?

In most cases I would say that you will not succeed. That's because most detectors rely on the TX coil inductance to set the TX frequency. If you put another brand coil on the machine, the TX frequency will be wrong and the RX circuitry may not be properly tuned for it.

But I believe the CZ's transmit a square wave and the TX coil is not part of the equation. Then it's down to whether the RX coil inductance matters, and I don't know. But I don't think it would hurt in the least to try. In fact, I have a CZ-7 and some Tesoro DD coils I could try to marry.

Interesting idea. Anyone else ever look at this?

- Carl

P.S. - shoot Fisher an email asking for the coil pinouts, they will probably tell you.

[will]

How 'bout a Minelab BBS or XT18000 coil? N/T

N/T.

[Dave Emery]

Re: Possibly modify elliptical coil for CZ ?

Carl,

Did you miss my post of November 16th to this site? I explained the coil connections for the Fisher coils by color coding of the wires. All the best, Dave. * * *

[will]

Re: Possibly modify elliptical coil for CZ ?

No, I didn't miss it. Problem is the coil to be grafted. Which one will work and what are it's pinouts. Also, that crispy critter bit sounds a bit iffy.

[Carl]

OK, I gave it a try...




I stuck my Tesoro 5x10 DD coil on my CZ-7. Once I got the RX coil polarity correct it actually worked! Almost.

Depth is actually pretty good, 8-9" on penny/nickel/quarter. However, discrimination is way off. Just about everything non-ferrous registers as silver, including pulltabs. Iron does signal as iron, though.

I suspect that the inductance of the RX coil is way off, and it throws off the RX phase that discrimination is based on. I might be able to tune this around with a cap box, so maybe I'll give this a try over the w/e.

BTW, coil pinouts are as follows:

CZ-7: 1/2 RX, 3/4 TX
CZ-6 (old?): 1/4 RX or TX, 2/3 TX or RX

I don't know which coil is TX or RX on the CZ-6 as I have a CZ-6 coil but no CZ-6.

Dave, I saw your post on the coil wires. However, you posted for the CZ-5/6 and I have a '7, and at some point Fisher used different connectors. My '6 coil has a female connector while my '7 coil is male. Plus, I cannot get the barrel off my '7 connector because Fisher filled it with silicone, thus I can't see the wire colors.

- Carl

[Carl]

More results

I added a cap box in parallel to the coil to move the phase response around. As I added in more capacitance iron started to move to the non-ferrous side so that tells me the inductance of the Tesoro coil is too high. The only way to try to fix this is go into the CZ-7 and retune the RX input. I'd rather not.

All of this suggests that if you get the RX inductance right (TX probably does not matter) you can probably make this work just fine. So, next task is to measure the inductance of the CZ-7 coil. This is something I've been wanting to do for a number of coils, so maybe I'll take a batch into work and hook up to the LCR meter.

It might be possible to lower the Tesoro inductance by adding a parallel inductor near the cable connector. Perhaps make an impedance matching box. As long as it's far away from the actual coil it will not be affected by mutual inductance effects and should be a classic parallel addition.

- Carl

[Carl]

Final results

OK, I measured the coils and, as I suspected, the Tesoro inductance is too high. Fisher RX measures 1mH, Tesoro RX is 11mH.

So I added a parallel inductor to the RX coil along with my cap box. With no additional capacitance non-ferrous had moved over to the ferrous side. I then dialed in caps until I got roughly the correct ID for my test targets. The only one that would not ID correctly was the square pulltab (showed foil), everything else was pretty much correct.

Is this practical? No! Adding the parallel inductor severely degraded depth because the inductor was causing power loss in the RX signal. You really need to get the RX inductance correct. For single frequency detectors you would also need to get the TX inductance correct. If I had a DD coil with about 1mH RX inductance I bet it would work just fine.

- Carl

[Rick, N. Mich]

Re: Final results

Thanks for the work you did trying to get the DD coil to work. If you do find a coil that works you would have a product you could develop and sell to us CZ users.

Have you been able to get the CZ6 coil working yet on the CZ7?

Rick

[Carl]

Re: Final results

>Have you been able to get the CZ6 coil working yet on the CZ7?

I have not tried. I need to order some connectors from SwitchCraft.