Pulse Detector Depth Proformance

[daverave]

Daverave what country you are residing now?

hello jladre....i live in the UK

[daverave]

i spoke today to the detectorist who made his own deep detector.....and he told me that part of his detector is based on the GS 5 but without the ground cancelling cause he is a beach detectorist...he showed me photos of the design where he has used plug in modules for each stage of the circuit...it uses an 18v battery pack...he also claims he got the capacitance of the coil low by say winding about five turns then he put an insulator material on top of windings and wound another say five turns by crossing over the first turns and st arting again from the start...then repeats again until he gets correct number of turns...he claims to get 24" now on a medium sized 9ct gold ring...he has got the thermal noise down to a low level...he is going to add discrimination modules to ID certain types of targets... but i think he cannot get around the iron problem so will use something maybe called a ferrous spear...to be honest it will be very hard now to compete with him and his two friends...as im not an everyday detectorist cause of my mood swings and anxiety...but im really trying now to push myself more and a very kind person has lent me a good pulse detector to try and if i can find some treasure will help cheer me up

[Ferric Toes]

i spoke today to the detectorist who made his own deep detector.....and he told me that part of his detector is based on the GS 5 but without the ground cancelling cause he is a beach detectorist...he showed me photos of the design where he has used plug in modules for each stage of the circuit...it uses an 18v battery pack...he also claims he got the capacitance of the coil low by say winding about five turns then he put an insulator material on top of windings and wound another say five turns by crossing over the first turns and st arting again from the start...then repeats again until he gets correct number of turns...he claims to get 24" now on a medium sized 9ct gold ring...he has got the thermal noise down to a low level...he is going to add discrimination modules to ID certain types of targets... but i think he cannot get around the iron problem so will use something maybe called a ferrous spear...to be honest it will be very hard now to compete with him and his two friends...as im not an everyday detectorist cause of my mood swings and anxiety...but im really trying now to push myself more and a very kind person has lent me a good pulse detector to try and if i can find some treasure will help cheer me up

Sounds like history repeating itself. In the 1990's I designed a Goldscan 4 detector with GB, then left off the GB and called that model Goldquest. I then uprated one of those with a 24V TX and had a separate RX winding with about 2 x the turns of the TX to increase the RX signal. That was the BeachBurner that I mentioned before. If I ever get the time, a BeachBurner 2 might be worth a try. You can also warm your hands on the coil on a cold day. For the moment though it will be interesting to see what the Vallon can do with a 15in coil. Still have to make the coil winding though and pot it.

There used to be a device called Ferrous Hound which was attached to a PI to give iron identification. Made in Australia by Reeve Jones. I don't know how effective it was.

Eric.

[daverave]

Hi Eric....i remember the ferrous hound and was very expensive...as far that i know that company does not exist anymore which is a shame...cause the ferrous hound with a good goldscan would be unbeatable combination...this guy told me that he is very impressed with the design of the GS 5 and i think a beach burner 2 will be an awsome machine !!!!!!! weather permitting will be going on local beach tomorrow and see what i can find.

[daverave]

Sounds like history repeating itself. In the 1990's I designed a Goldscan 4 detector with GB, then left off the GB and called that model Goldquest. I then uprated one of those with a 24V TX and had a separate RX winding with about 2 x the turns of the TX to increase the RX signal. That was the BeachBurner that I mentioned before. If I ever get the time, a BeachBurner 2 might be worth a try. You can also warm your hands on the coil on a cold day. For the moment though it will be interesting to see what the Vallon can do with a 15in coil. Still have to make the coil winding though and pot it.

There used to be a device called Ferrous Hound which was attached to a PI to give iron identification. Made in Australia by Reeve Jones. I don't know how effective it was.

Eric.

Hi Eric...have you considered trying a 15 x 12 coil with the vallon...i used a 15 x12 sef coil cover to make a coil for one of my surf pi and i noticed the depth increased compared to a round coil.

[ionut_mtb]

i spoke today to the detectorist who made his own deep detector.....and he told me that part of his detector is based on the GS 5 but without the ground cancelling cause he is a beach detectorist...he showed me photos of the design where he has used plug in modules for each stage of the circuit...it uses an 18v battery pack...he also claims he got the capacitance of the coil low by say winding about five turns then he put an insulator material on top of windings and wound another say five turns by crossing over the first turns and st arting again from the start...then repeats again until he gets correct number of turns...he claims to get 24" now on a medium sized 9ct gold ring...he has got the thermal noise down to a low level...he is going to add discrimination modules to ID certain types of targets... but i think he cannot get around the iron problem so will use something maybe called a ferrous spear...to be honest it will be very hard now to compete with him and his two friends...as im not an everyday detectorist cause of my mood swings and anxiety...but im really trying now to push myself more and a very kind person has lent me a good pulse detector to try and if i can find some treasure will help cheer me up

what size have his coil? the bigger the coil, bigger the depth. of course not sensible for small gold items like earrings.

[daverave]

what size have his coil? the bigger the coil, bigger the depth. of course not sensible for small gold items like earrings.

He has made a 14" coil using home made litz wire and used carbon fibre tape for the screening and he has got the coil capacitance down...and the coil only weighs about 250g and is ultra light from what he has told me...i saw photo of coil and it looks very good...and he said coil inductance is around 380 uH but has managed to get the coil working at 9 uS...i think he has got good sens on small gold...he claims 24" depth on a 9ct medium size gold ring like a whisper...him and his two friends have the edge now on the beach as one of his friends has a whites tdi sl and has done very well with this machine...with the machines ive made i cannot really compete and some of these guys go out detecting nearly every day.

[bklein]

I find it hard to believe that most of the rings are too deep for a surf pi. I would get depression too if I had to dig 20" for every target - I'd give up this hobby quick. It is better to have a detector with discrimination and reasonable depth than one without and goes too deep. I think you will find it is more a matter of specific hunting area, then the area covered - either because the other guys get out more often than you do, don't dig questionable targets, have a larger diameter or bigfoot coil, etc. A CTX is a well respected and successful detector in the UK but a pi senses deeper and handles black sand better. A pi is a fine lightweight machine for you. Maybe give up beaches and hit parks, concert sites, or old properties instead for a change of pace. Just try and find places not loaded with pulltabs and aluminum or your depression might get worse. That Whites Classic1 can at least discriminate out the pulltabs - it actually is decent for recent find hunting. Maybe bring a ring with you and test where you hunt so you have confidence you can find others just like it within depth range.

[6666]

He has made a 14" coil using home made litz wire and used carbon fibre tape for the screening and he has got the coil capacitance down...and the coil only weighs about 250g and is ultra light from what he has told me...i saw photo of coil and it looks very good...and he said coil inductance is around 380 uH but has managed to get the coil working at 9 uS...i think he has got good sens on small gold...he claims 24" depth on a 9ct medium size gold ring like a whisper...him and his two friends have the edge now on the beach as one of his friends has a whites tdi sl and has done very well with this machine...with the machines ive made i cannot really compete and some of these guys go out detecting nearly every day.

Hi Dave would you mind asking your friend the details and brand of that carbon fibre tape please , sounds like it could be interesting to try out.

[ionut_mtb]

He has made a 14" coil using home made litz wire and used carbon fibre tape for the screening and he has got the coil capacitance down...and the coil only weighs about 250g and is ultra light from what he has told me...i saw photo of coil and it looks very good...and he said coil inductance is around 380 uH but has managed to get the coil working at 9 uS...i think he has got good sens on small gold...he claims 24" depth on a 9ct medium size gold ring like a whisper...him and his two friends have the edge now on the beach as one of his friends has a whites tdi sl and has done very well with this machine...with the machines ive made i cannot really compete and some of these guys go out detecting nearly every day.

i have made an 8" 3dss coil, selfshielded?? (chance pi coil by baum7154) don't know the exact inductance, 1.2mm diam stranded litz wire with pvc insulation, so quite few ohms and with baracuda PI goes up to 30cm for a coin, and very sensitive to small stuff. It goes down under 10us as i measured with the scope (novice, bought it 2 days ago). I will try to make in the future one coil double the size (16") and i'm expecting double the distance for targets. i'm not interested in nugget hunting so, for the gold rings i thing will have good depth.

[daverave]

Hi Dave would you mind asking your friend the details and brand of that carbon fibre tape please , sounds like it could be interesting to try out.

i dont really see this detectorist much but i will try and get some info for you if possible.

[daverave]

i have made an 8" 3dss coil, selfshielded?? (chance pi coil by baum7154) don't know the exact inductance, 1.2mm diam stranded litz wire with pvc insulation, so quite few ohms and with baracuda PI goes up to 30cm for a coin, and very sensitive to small stuff. It goes down under 10us as i measured with the scope (novice, bought it 2 days ago). I will try to make in the future one coil double the size (16") and i'm expecting double the distance for targets. i'm not interested in nugget hunting so, for the gold rings i thing will have good depth.

ive always found it difficult to get 10 uS delay...if i go below say 14 uS then the detector will pick up salt water....ive never used litz wire...but only normal copper wire and teflon multi strand types.

[green]

i have made an 8" 3dss coil, selfshielded?? (chance pi coil by baum7154) don't know the exact inductance, 1.2mm diam stranded litz wire with pvc insulation, so quite few ohms and with baracuda PI goes up to 30cm for a coin, and very sensitive to small stuff. It goes down under 10us as i measured with the scope (novice, bought it 2 days ago). I will try to make in the future one coil double the size (16") and i'm expecting double the distance for targets. i'm not interested in nugget hunting so, for the gold rings i thing will have good depth.

I saved a copy of a chart(detection distance vs coil diameter) that has been posted a number of times. Suggests a 30% increase in detection distance not double for a 16 inch coil compared to 8 inch coil. Maybe someone knows where to find the chart.

[ionut_mtb]

ive always found it difficult to get 10 uS delay...if i go below say 14 uS then the detector will pick up salt water....ive never used litz wire...but only normal copper wire and teflon multi strand types.

i have to say that i did not test the detector outside, measurements are only indoor made, air tests. i've just constructed the detector/

[kt315]

I saved a copy of a chart(detection distance vs coil diameter) that has been posted a number of times. Suggests a 30% increase in detection distance not double for a 16 inch coil compared to 8 inch coil. Maybe someone knows where to find the chart.

ok. it was Eric answer done in Findmall forum. i repeat it. with text.



Re: Question on coils
Posted by: Eric Foster
Date: May 18, 2005

Here are the curves I have used for many years. The range reaches a maximum when it is equal to the radius of the coil. Coils larger or smaller than this optimum will result in less range. To show how this works, along the bottom axis you see coil diameter, which is obviously 2 x the radius. So for an 11in coil, if we go up the vertical scale to A, we have 5.5in. Also note the diagonal line and the series of ever increasing semicircles. Everything to the left of this line shows increasing detection range up to the maximum where it intersects the line, then decreasing range to the right, where the semicircles are shown dashed.
If a certain metal object is just detected at 5.5in with the 11in coil, then going larger in coil size will cause a reduction (going down the dashed side), and going smaller in coil size will have a similar effect. Initially, it won’t be much, i.e. going from an 11in to an 8in coil will only make 0.5in difference but below 4in diameter, the range will drop rapidly.
Now, suppose with the 11in coil, you can detect an object at about 12.5in (B on the vertical scale. This indicates that the coil is not an optimum size for that particular object. If we carry on up the curve (direction of arrow) we can see that by using a 20in coil, we could gain another 2.5in (C). The curve peaks at 15in with a 30in coil. But the extra inch gained hardly makes such an unwieldy coil worth while.
Other factors come into play of course. The curves assume that the number of turns and the coil current is the same in all cases; which it isn’t necessarily. For the same inductance value, a smaller coil has more turns, which counteracts to some degree the loss in range. Also a smaller coil will pick up less electromagnetic noise, earth’s field noise and ground effect, which make for a smoother threshold.
The end result is, that with a small nugget that can be detected at between 5 and 7in with the 11in coil, so that it is on the top part of the curve, an 8in coil may well give a similar range. That is not to say that smaller coils do not have other advantages. Small coils and probes are very useful in rocky areas or searching in undergrowth. They have less drag too for water hunting, and less pickup from mineralised soil or conductive sea water plus better signal separation on close or multiple objects.
One other point regarding PI, is that the small object sensitivity is largely determined by the sample pulse delay. If an object is so small, or thin, or made of high grade stainless steel, such that all the signal has decayed before sampling takes place, it would not matter how small a coil you made, it would never be picked up.
Eric.