Surf Pi Professional Pcb's back in stock - NEW Prices

[Waikiki_Sweep]

Cat7 cables come with wire shielding, so in order to make a real shielded coil you'll need less than 20ft of such cable and some smart wiring. How about that

Interesting idea. Probably you can make a coil with using 2-3 loops of such cable.
It may work if you want to push such cable inside plastic pipe.

But probably the results will be away from optimum:
1. Massive cable shield will keep eddy currents flowing inside the shield and make coil slow.
2. Stray capacitance between twisted wires will delay decay and make coil slow.
3. Stray capacitance between wires and shield will make coil slow.
4. You will have 8 soldered connection inside the coil so you have to insulate it good
or you will have some falsing and noise from moisture or current leaks.

But you can try and compare it with another coils. May be it is not so bad.

Anyway it is not good to use in water because it will be as bulky
as any one stupid brand name detector coil and you will hate it once you will try to move it in water

[Davor]

Cat7 cables come with wire shielding, so in order to make a real shielded coil you'll need less than 20ft of such cable and some smart wiring. How about that

[Waikiki_Sweep]

Thanks, let me ask. Are you using 1 wire to make your coil or 2 wires? Let me explain when you buy the network cable, inside are 4 pairs of 2. Your coil is make of 1 pair of 2 of those 4 pairs? Or you do the same I did, I separate the 2 cables of that 1 pair of
2 and use only 1 wire to make my coil.

Yes. I have untwisted wires using electric drill. Sure it is a lot of work so it is better to buy 75 ft. network cables to save time because to make a coil you need only 55-60 ft. of wire in one piece. One cable let you make 8 coils. (8 wires in 4 pairs)

[6666]

Hi Jim
thanks for the info, I will try that coil also
cheers
6666

[TH Jim]

@ 6666

Hi 6666, No, it's my smaller coil that is currently on the Surf PI Pro and sampling at 12uS, I think it's roughly 6.5 x 8.5 inch, 23 turns, .4mm. The larger coil will probably also sample at that delay but I built it for the Baracuda and havent tried it on the Surf PI yet. No longer have the Baracuda and can't remember what was the minimum delay i could achieve.

Cheers, Jim

[der_fisherman]

I guess I will be back later because here in Puerto Rico is 11 in the morning. And maybe all of you are sleepin. So I will be back in the night.

Unlikely, most of the western world will be awake!
I received the notification of your post at 19:50 local time Friday.....I am on Middle European Time, which is GMT +2 in the summer (Summer Time). We are 6 hours ahead of you I believe.
that would imply that at 11.00 am your time, the UK would be at 16:00 amd the rest of Europe at 17:00.
The USA would around the same time or mostly earlier......
regards
Andy

[goldstar]

Thanks, let me ask. Are you using 1 wire to make your coil or 2 wires? Let me explain when you buy the network cable, inside are 4 pairs of 2. Your coil is make of 1 pair of 2 of those 4 pairs? Or you do the same I did, I separate the 2 cables of that 1 pair of
2 and use only 1 wire to make my coil.

[Waikiki_Sweep]

I guess I will be back later because here in Puerto Rico is 11 in the morning. And maybe all of you are sleepin. So I will be back in the night.
My configuration with my 8 inch oval coil.
My P1 =100k [Trimmer] is on the midle
My P2 =10k [Tune] I'm using a little bit of noise so I can hear the sound when gold is near
My P3 =100k [Delay] is off completlly. And I'm gettin the gold, I wll check the resistor to make it more sensitive to gold.

Usually round coils give more depth than oval coils but oval coils cover more ground in one sweep. I like long coils that cover more ground even if there is no maximum depth to go faster. So you can choose what you want: speed or depth.

Get rid of 100k P3. Put 15-20K on P3 instead. And adjust it to have maximum sensitivity.
Replace R25 on 5.1k.
Even small difference from 0k to 10k of P3 will give you changes in sensitivity to gold in two times. 100k in full range will discriminate gold out completely.

Maximum sensitivity it is not always minimum value of P3. Only with 15-20k pot you can find that peak precisely but not with 100k.

Also there may be something wrong with this medallion too. Cavities, bad metal composition making it high resistive. Try it with gold ring or better with several different gold rings to be sure.

What about health of your detector?
Did you set zero offset on preamp?
Did you fixed that R18, R22 error on Longboard?

http://www.geotech1.com/forums/showpost.php?p=145375&postcount=176

Try it with different coins, bottle cup, e.t.c.
Do you have 25-30 cm. for 1 euro?

If everything works OK and assembled correctly you can try to rise sensitivity:

- You can change integrator values and add sensitivity pot like you can see it on PRO schematics.
- You can try increase pulse width changing 3.3k to 4.3k, 5.1k.
- You can try to increase dumping resistor from 390 to 430, 500 ohm. With some coils I even using 900 ohm.

All those measures can make your detector unstable so use it carefully to keep it working on the edge with maximum sensitivity but reliable.

[goldstar]

I guess I will be back later because here in Puerto Rico is 11 in the morning. And maybe all of you are sleepin. So I will be back in the night.
My configuration with my 8 inch oval coil.
My P1 =100k [Trimmer] is on the midle
My P2 =10k [Tune] I'm using a little bit of noise so I can hear the sound when gold is near
My P3 =100k [Delay] is off completlly. And I'm gettin the gold, I wll check the resistor to make it more sensitive to gold.

[goldstar]

I have no problems to detect gold with my PI. Any gold. 10k, 14k, 24k. And more. Most of gold rings I am detecting from distance 1.5 times far then distance I detect coins.
First of all I am using short delays. 20 micro seconds or less. Check your R25 and delay pot P3 (hear input 8 of U4C - MC14093). If you have it 15k + 100k it is just wrong.

Every 1 kilo Ohm in R25 + P3 chain is practically equal to 1 micro second of delay.

So if you using 15k + 100k in max range it will give you more than 115 micro seconds that is far away from gold ring decay time and good to detect coca can .
You will never set precise delay with such range.

Check original Surf PI Pro schematics below. It has 5.1k + 10k pot on the place instead of 15k + 100k pot for version we all building till now.
I am using 7.5k + 22k pot to be able adjust delay in range I need but only because I search in salt water. For dry sand 5.1k + 20k pot will be OK.

Also I think that coil design is important too. If you using single AWG 24 wire, not stranded, it will decay as long as your gold ring.
If you have connected coaxial cable straight to the coil than shield
in your coaxial cable will keep eddy currents even longer than gold ring decays. I am using twisted pair of stranded wires to keep coaxial shield away from coil.

Regarding chains. It picks chains with very short delays. And as delay shorter distance of detection of chain increasing.
With longer delays it can't be detected at all. Consider chain as a very small gold rings that decays very very fast.

Thanks I did read all your post and I just follow everything you wrote so I reshape my coil I use 24 awg wire "because "I. Was using 22awg " so I buy the same you post and I make an oval coil using 8" diameter coil and I detect a small 14k medallion at 3 inches. I did work on the delay to make it shorter. And I haven't check the resistor you are talking about. So maybe its better to use the oval coil or I think because the 2 sides of the coils are near an when the gold pass its making the gold more detectable. I'm going to post some picture of the coil and all my findings and the mesaurments when I sit on the computer because now I'm using my phone. The surf pi works we have to give time.

[6666]

My coil will allow me to sample down to 12uS, using a 5k1 and a 10K pot for delay adjustment. 12uS provides good sensitivity to gold and all other small iitems.

TH jim was that your 10x8 elliptical coil 21turns .4mm ?

[Qiaozhi]

Cool. I think the RX has a damping resistor in the coil but needs another at the preamp input. (I proved that by scope shots in one of my other threads). With the TX this way, is there the same concern to damp the flyback pulse? Lessening or eliminating it would save power. Probably some interference to the RX side though.

Both the TX and the RX coil need to have a damping resistor. Although there may be a resistor in the coil shell, it may not be the correct value for the Surf PI circuit.

[bklein]

Cool. I think the RX has a damping resistor in the coil but needs another at the preamp input. (I proved that by scope shots in one of my other threads). With the TX this way, is there the same concern to damp the flyback pulse? Lessening or eliminating it would save power. Probably some interference to the RX side though.

[Qiaozhi]

How may a DD coil be incorporated with the Surf PI circuit? I have a couple Minelab DD coils I want to compare without messing with the Minelab detector.

Yes it is possible to use a DD with the Surf PI.
You will need to break the track between the 1k resistor [this is the input resistor connected to pin 1 of the NE5534] and the coil. Then attach the RX coil to this resistor.

In other words, for a mono configuration, the coil is being used as both the TX and RX. For a DD coil you need to split these functions so that only the RX coil is connected to the input of the preamp. And ... don't forget that the RX coil will also need to have a damping resistor fitted.

[der_fisherman]

How may a DD coil be incorporated with the Surf PI circuit? I have a couple Minelab DD coils I want to compare without messing with the Minelab detector.

My personal take is that it cannot as I believe the Surf PI is a Pulse Induction and as far as I am aware, true DD coils are for IB/VLF machines.......
I hope this helps
Andy