why

[Aziz]

"More power" is gaining more under certain conditions.
But this can only be answered and really proven by a real "coil meister"(c)(r)(tm).


(Hey forum-trolls!, it's your turn now (you know, you must motivate me). *LOL* )
^sif,
has more (brain) power *LOL*

[Koala]

Would it be possible to design a rig where the current and peak to peaks could be altered to test in the real world.

Silver Dollar has just got an original Bandido I know it's not the deepest detector in the world but he measured the peak to peak at under 8V and Tesoro use very thin wire for the transmit so not all that much current either.

Does the improved signal to noise of surface mount technology in a modern detector make much difference?


It's probable not one thing but lots of little things that add up to make a difference.


Would like to test my rig on a hammered in the ground but I normally detect on the beach at the moment. Have got a 1916 sixpence. I don't measure how deep things are when detecting but guess about 6" so maybe 10" on a full hammered that's not damaged and is lying flat is not unrealistic.

[Henrikras]

It could Be a Very Interresting test this; Flat side "one coin" and this coin only the size so Big, that a 8" depht was the excatly maximum.. Then place the same coin in the same hole in same depth but now at 45* Angle... What would you think was possible now ? 6" I would geuss.
Thats why every depth test should Be with a 45* angle, because there is a great deal much bigger chance to find a coin at 45 than on the flat side or total vertical. The two most rare angles theory representation, which may occur, is flat side and 180* (vertical).
I dont think the will much lose before the coin tip over 30 degress, and again the lose from 60* up to vertical will Be the must.
I could Be Very wrong, but the Message is.. The angle got a lot to say..
Henrik.

[Skippy]

Quote:"Would it be possible to design a rig where the current and peak to peaks could be altered to test in the real world?"
Not that easy to do, changing TX strength whilst changing RX gain by the corresponding inverse amount.
But... the XP Deus has this feature as standard, I believe. There's three power levels, intended to make the most of the available small battery. And reports from those who have tried it suggest there's no difference.

[Henrikras]

Just excatly Skippy no different in the field with TX 2 or TX 3 at the Deus, only that the Battery goes empty faster.
TX 1 can Be measured with a little less depth. Picture was the scope work with the Deus 11x13 Stock coil.
TX 1 = 10vPP / TX 2 = 15vPP / TX 3 = 18vPP
Henrik.

[Koala]

Henrik
Kinda all ready know part of the answer. Just found out that the Uk 10p now have an iron core. I went out and tested one on the ground. When flat it's easy to detect in disc mode well over 6". However up right it's almost undetectable in disc mode

Skippy
Thanks thought that might be the case after seeing the Bandido but it's good to have it confirmed

[Silver Dollar]

I'd have thought most coins land flat. I guess I have to get out in the field more often.

The TX power is governed by that x6 thing so needs x64 to get double the depth. The
real trick is how much current is in the coil? A stock TGSL oscillator draws ~2ma and puts
32 ma into the coil. The H bridge draws 7 ma and puts 150 ma into the coil. Just raising the
voltage won't raise it as much as designing the oscillator to keep the current in motion...

[Koala]

"I'd have thought most coins land flat. I guess I have to get out in the field more often"

On the sandy beaches most I find are

Think it depends what type of detecting you do. Plowed land has to be random. You normally find most are flat. This I assume is because none flat coins are missed due to being such a difficult target to detect. Also when a field is re-plowed there are new finds. Some will have moved in depth but some will have just rotated to be more flat so easier to detect.

Have to do some tests on different angles with different coil size and see if a smaller or concentric helps. Maybe just going for depth means a lot more are being missed.

[Aziz]

Hey guys,

you can forget the '"x64-rule" (or the sixth power rule) with large coils.

^sif,
the master of coils *LOL*
(I'm teasing all the gurus, yep, I'm the legendary "coil meister"(c)(r)(tm) *LOL* )

[golfnut]

on the coins, yes they may land flat but they tumble as they sink and worm action can bring items up.

Yes ploughing spins the top 6 to 14" inches every year for countless years


A recent mod to a 250 using a nel coil gets thin silver edge on well

Ive got to make a new machine... or buy one like a GMP -- is poss to alter the Tx freq on a GMP to say 15kHz or is it derived via a clock/cpu ?

S

S

[Skippy]

Re: changing the freq of a GMP: It's so near, but so far, I think. The circuit board and 95% + of the components are identical to the GMAXX2, so you would think that it would be a good candidate for a custom frequency...however the microcontroller is programmed differently for each model, so that ruins that plan. Why would you want it to run at 15K, it's going to be hardly any different, performance-wise to 18K anyway.

[hoadlies]

Quote:"I wonder if the designers of detectors are overly-concerned about battery hours of use????..as today we have a plethora of battery options ,Rechargables ,lithium ,etc"
This is rather self-contradicting - now is the time when power-hungry electronics are much more viable, due to the better batteries.
Sadly, detection depth is not really "power sensitive", it's simply a case of finding very small target signals in the presence of a reasonably significant ground signal. "more power" just increases the ground signal, and the target signal, by the same amount, gaining you nothing. There are some gains that result from more TX power: electrical interference (radio freq, electric animal fences etc) becomes less of a problem, and circuit noise on the RX side (resistor noise, semiconductor noise) is not so important.
But to take the F70 as an example, about 10 milliwatts (might be less) of battery power ends up in the coil, mostly warming it up. The rest of the electronics takes an impressively low 250mW (hence the 30+ hours on 4 x AA cells).

THANKS for that explanation ''SKIPPY'' I have much to learn on M/D requirements & AS YOU SAY POWER INCREASE IS NOT GOING TO HELP BY ITSELF ..
Thats cleared that up for me ..

This a a most interesting thread so I will read-on ..

CHEERS TO ALL,,,,,,,,,,,,,,BARRY..

[Henrikras]

The best posible hand made searchcoil and the Q factor !!! Any got an idea how must its got say Winding a Very good coil with highest posible Q in a selected form ? Does it effect the depth with a poor Q ?
Is the RX Q more important than the TX Q ?
In those coil I just made, Skippy learned me that I can reach a higher Inductance Winding the coil tight, and that must give a higher Q ?
Is it possible to measure the Q at a Stock coil.
I dont know how much the Q got to say, but If ! The isolation lak at the wires need to be thin as possible, that would give a thinner coil and better Q or not ? But those wires can only be buyed in a standard version or not ?
I'm just thinking... We can have the best Detector in the World, but If our coil isn't made perfect we will lose a lot.
Henrik.

[Skippy]

If you are making a coil for an existing commercial detector, then you have to make it with the same Q-factor, if you don't, you will likely find discrimination is upset, ID values skewed etc.
I personally think excessive Q is not helpful. The resonance becomes easily disturbed by the ground, and iron in the ground, with follow-on effects on synch detectors, discrimination etc. Keeping Q in the 10 to 20 area seems OK, and it's what top end commercial machines use.

[Henrikras]

Thanks Skippy... Thats why we need to make some good tight windings, because the factory made coils is made by a machine and are close to perfect made. Thats why I had trouble in the begining with my Deus coils, until I mastered to make tighter made coils.
Can I please get some help with this.. I Need to understand and learn this subject;
This is a Link to a Q Calculator : http://www.pronine.ca/qbw.htm
This is the values at my Stock RX coil; C: 15 nf and L: 15.9 mH, that gave me 10.3 khz in resonans. My L got 70 ohm in DC resistance...
If I enter those into the Calculator it gave me a resonans 10.28 khz.(the same results my LC gave me by scope/tonegenerator).
The Calculator said a Q at 12.77. But the I needed to enter 0 ohm at the RC !! Is that right ?
One other RX coil I made with all the same values unless the R, it was lower 50 ohm. If I try that my Q goes up to 16.98.
This RX coil is working and why must be what you say Skippy, that a value from Q 10-20 is acceptable...
My quenstretion is now... Would I had made a more sensitive searchcoil with a higher resistance (R up to 70ohm) and a lower Q and had a possibility better depht, or would you say that the different isn't to be measures and in performance ?
Thanks.
Henrik.