Question about Mono and DD coils on the GQ

[colt]

I have been using an 11" mono coil on my V2 and in some areas it will have more static, but provides good depth, when I switch to an 11" DD coil, it will have a lot less noise, but my depth will be reduced by about two inches, I know this because I have placed a nickel on the ground and performed some testing.

So my question to the more experience GQ users is, at what point will the DD coil out perform the Mono coil. Maybe the soil conditions in the area that I am prospecting in, is not at the tipping point where the DD coil is a the better choice.

colt

 

[Buz]

Hi Colt

First off sorry to hear about your dog,I lost my pal after 14 years. I haven"t noticed any depth loss using a DD coil on my GQ,just runs a bit quieter.


Buzz(ID)

 

[colt]

Thanks Buzz, what size of coiltek do you run, is it the elip of round. I been looking at the coiltek 14" elip, I am going to the big prospectors shin-dig out at Stanton, AZ. next weekend, some of the venders are going to set up test areas, for people to test coils.

I am also interested in the 10" elip and the mini ufo, man the problem is so many coils on the market. I would like a small coil for tight areas and one large coil for more open areas for coverage. I have to say, I like the stock 11" mono that came with the GQ, it is very sensitive and gets good depth.

colt

 

[Buz]

Cole
It's a Platypus coil, and the reason I bought it was the coil is waterproof and it fits the bill, it measures 9x 12 and elliptical
Reg built me a 11 inch round DD coil that works just as good as the coiltek but not waterproof.

Buzz

 

[Kev]

Hi Colt,
When you get numerous targets that sound like a 1 grammer at 7 inches, but on digging find nothing, you then need to switch to the DD. Otherwise the mono is the better choice.

Cheers
Kev.

 

[Buz]

n/t

 

[Kev]

Hi Buzz,
Mine is a GQV1 with a DD mod also. The V2 has the extra filter added to the SAT, and a new PCB spin with the damping trimmer incorporated, plus a few other minor changes. I tried a similar filter on mine, and found that while it helped with ground noises, it attenuated the signal too much. I have achieved similar benefits with the compression diode across the pre-amp, and increased DC gain, without the signal loss of the filter.

Cheers
Kev.

 

[Buz]

Hi Kev
When you talk about compression diode, are you talking about a thermionc valve?



Buzz

 

[Kev]

Hi Buzz,
See my post "Omitted an important detail" on the 16th of January.
The brd shown uses 2 BAV99 diodes so it's actually two forward conducting diodes in series, parallelled with two reverse diodes in series. A 500k to 1Meg trimmer is better too.

I recently tried a single schottky in reverse mode with 2 forward series, but it didn't work any better. This circuit also requires the gain of the DC amp (the one after the integrator) to be increased from 48 to 88 to make up for losses.

I'm finding gold slightly deeper with this arrangement.

Cheers
Kev.