Delta Pulse

[kt315]

DP is predominately a RELIC (or deep cache, or coins) hunter. (Am I right, KT315??) Do not expect to find a fine gold ring with it, you will probably be disappointed. (That is only my opinion. Some maniac might be able to make me eat those words.)

do not see a problem to set a additional knob, simplest mod, by one click it will choice either deep cache or coins.

[mohandes]

Also, Mary, Joe, Tom, and Ezekiel; all of them want for me to be able to simulate their exact circumstances (ha ha). Problem is (one problem, anyway), each of them is incapable of describing the exact circumstances. Another problem is that I don't have TIME for it... and I probably would prove not to be smart enough for it even if I did have the time.

To answer one question, I think that stth12R06D should absolutely be able to withstand any stress Deltapulse PI demands of it (provided that you are using IRF740 MOSFET), but whether or not it would makes things work better, can only be determined by you, by your real-world tests.

You may be able to tell everybody how much inductance and resistance is in your coil, and you may also be able to tell everybody how much resistance is in your cable, (and to be honest, that aspect of the problem had not cross my mind before you mentioned it, and it is also important), but nobody can ever know how much CAPACITANCE is in your coil/cable combination. Very much, too, too, TOO, much guesswork is involved for anybody to be able to determine that for you.

Maybe you should try a shorter length of cable, because 3.5 ohms does seems a bit too much, but then, I have not measured any coax's resistance lately. But, you did not tell what type coax you have, or how long it is (not that I want to want to know)!!

Come on, give us all a break. Spice is a general tool... you ask for detailed answer, but at the same time, you can provide only basic/general information. That is unreasonable.

Here's what I think: All anybody can do is to try and use the best available materials and use the best construction techniques that you can muster. If you have knowledge about the characteristics of the materials you are using, and how your construction techniques react with those characteristics, you can use your best approximation in a simulation to try and find out which direction you need to go. But, NEVER should you expect detailed answers. Hope for the best, but test your test results in a real world scenario ASAP.

GIGO means "Garbage In, Garbage Out". I apologize if I made my it appear that a simulations does not obey that very, very basic rule.

edit: Find out how to measure the resonant frequency of your coil/cable combination. When you can do that; by doing that, you can generally determine the relative merit of the coil/cable combination.

(All other things being the same) making the resonant frequency go higher should result in a better coil... a better coil should result in the capability to take your primary sample sooner in time (having a shorter sample delay).

It is generally considered that a shorter sample delay results in better sensitivity, but I think that that depends on WHAT you are searching for, and also depends on the particular detector you have in your hands!

From what little bit I know, I think that DP is a different animal... it definitely is not, I repeat, NOT comparable to the likes of either Surf PI or the Barracuda... (unless you don't mind comparing apples and oranges... only my humble and untested opinion).

DP is predominately a RELIC (or deep cache, or coins) hunter. (Am I right, KT315??) Do not expect to find a fine gold ring with it, you will probably be disappointed. (That is only my opinion. Some maniac might be able to make me eat those words.)

thanks , and excuse for my English.
i use military ICs , 4538 and 4066 and lf357. I use ne556 and ne555. all res is 0.1percent .
i use military irf740 ( master ) and can produce to 620Vp-p .
use two mode frequency in 500 and 130hz .PW at 90mks to 270mks .
and tl072 i think better than tlo62 , what is your idea ?
regards

[green]

Is somebody trying to pay me back for giving them a headache? (Just kidding, but that chart could give somebody a serious headache.)

I apologize for giving you a headache.I was trying to reply to Tepco"s reply #2628

[Under very long pulse condition, large amount of energy released, diode may enter so called “avalanche mode”, at least this particular type. Normally, computer simulation will fail to predict this. Under this condition, circuit behavior can change slightly, producing that famous 1500V peak and significantly influencing detector behavior. Someone with suitable hardware should provide scope pictures, eventually experiment with other diode types under various conditions. Some modern fast diodes are specifically designed to avoid avalanche, ordinary slow types can reach this mode easily, recommended diode is probably somewhere between. It is less known that ordinary 1N5408 rectifier, otherwise too slow to rectify even at audio frequencies can produce very high power nS pulses in avalanche mode. Experiment with different types can be interesting, at this point ignore capacitance and switching speed, try some ordinary ones too.]

I recorded scope wave forms, reply #2631with some different diodes. Adding a MUR460 diode increased the circuit resonance from 345khz to 1.3Mhz. The amplifier out vs time chart in reply #2634 was done to show if there was any improvement with the diode. The sample delay could be decreased from 9 usec to 4 usec . Adding the diode reduced the signal probably by reducing the voltage to the coil. I have been using the diode to get a short delay, but it looks like it hurts except for short TC targets. Sometimes a picture is worth a thousand words, sometimes not.

[porkluvr]

hi
dear friend i use 450ohm for damping res and my coil near 460mkh and 2.2ohm ( plus coaxial cable near 3.5ohm )for 28cm coil. and this value is best result for my DP.
i test with 680 , 750 and ...1.2k but best result in 450ohm in AIR testing.
i can not find stth1210D in my country so i buy stth12R06D , Do you thing it is work or burn ?
and in finally , Diode help for faster respond and i think can better for Depth , i say OK ?or better say diode cause DP work better ?
can you simulation with my value i say you above and post here.i want know 450 ohm ok or 680 ohm.
regards

Also, Mary, Joe, Tom, and Ezekiel; all of them want for me to be able to simulate their exact circumstances (ha ha). Problem is (one problem, anyway), each of them is incapable of describing the exact circumstances. Another problem is that I don't have TIME for it... and I probably would prove not to be smart enough for it even if I did have the time.

To answer one question, I think that stth12R06D should absolutely be able to withstand any stress Deltapulse PI demands of it (provided that you are using IRF740 MOSFET), but whether or not it would makes things work better, can only be determined by you, by your real-world tests.

You may be able to tell everybody how much inductance and resistance is in your coil, and you may also be able to tell everybody how much resistance is in your cable, (and to be honest, that aspect of the problem had not cross my mind before you mentioned it, and it is also important), but nobody can ever know how much CAPACITANCE is in your coil/cable combination. Very much, too, too, TOO, much guesswork is involved for anybody to be able to determine that for you.

Maybe you should try a shorter length of cable, because 3.5 ohms does seems a bit too much, but then, I have not measured any coax's resistance lately. But, you did not tell what type coax you have, or how long it is (not that I want to want to know)!!

Come on, give us all a break. Spice is a general tool... you ask for detailed answer, but at the same time, you can provide only basic/general information. That is unreasonable.

Here's what I think: All anybody can do is to try and use the best available materials and use the best construction techniques that you can muster. If you have knowledge about the characteristics of the materials you are using, and how your construction techniques react with those characteristics, you can use your best approximation in a simulation to try and find out which direction you need to go. But, NEVER should you expect detailed answers. Hope for the best, but test your test results in a real world scenario ASAP.

GIGO means "Garbage In, Garbage Out". I apologize if I made my it appear that a simulations does not obey that very, very basic rule.

edit: Find out how to measure the resonant frequency of your coil/cable combination. When you can do that; by doing that, you can generally determine the relative merit of the coil/cable combination.

(All other things being the same) making the resonant frequency go higher should result in a better coil... a better coil should result in the capability to take your primary sample sooner in time (having a shorter sample delay).

It is generally considered that a shorter sample delay results in better sensitivity, but I think that that depends on WHAT you are searching for, and also depends on the particular detector you have in your hands!

From what little bit I know, I think that DP is a different animal... it definitely is not, I repeat, NOT comparable to the likes of either Surf PI or the Barracuda... (unless you don't mind comparing apples and oranges... only my humble and untested opinion).

DP is predominately a RELIC (or deep cache, or coins) hunter. (Am I right, KT315??) Do not expect to find a fine gold ring with it, you will probably be disappointed. (That is only my opinion. Some maniac might be able to make me eat those words.)

[porkluvr]

Recorded more data. No diode vs MUR460. Didn't get what I expected. Thought the amplitudes would be the same at longer delay times. The no diode recordings are higher. Using pi*L uh*circuit resonance Mhz(no R damp) to calculate R damp. No diode=303 ohms, MUR460=1100 ohms. I used 286 and 1000, a little over damped. I already had a 1k resistor for R damp, paralleled 1k with 400 for 286 ohms The diode in series reduces the current at turn off, might be the cause for lower amplitude. Used a 6 volt supply, 12 volt supply might have less difference. Any other thoughts would be appreciated.

Is somebody trying to pay me back for giving them a headache? (Just kidding, but that chart could give somebody a serious headache.)

[kt315]

but why 450ohm work better ?

that is only your subjective perception. fantazy. in original schematic Rd value is 820 Ohm. for DP working on long MAIN SAMPLE DELAY the ringing is not so actual
like may be for Surf PI, Bara, HH etc. from your pic BMP clearly seen that if you set MSD on 40us (really practically I set on 100-120us) the ringing is leaving at left on timing and not effecting.

[mohandes]

This looks reasonable, actually surprisingly fast. If you measured this with coax cable connected leave it as is, some ringing on waveform wont hurt, eventually reduce Rd to 680 ohm.

yes , you learn me before , i change it with 680 ohm and next 450ohm , and next see in scope , both of them have a same respond in scope ( less than 15mks ) but why 450ohm work better ?
regards

[Tepco]

This looks reasonable, actually surprisingly fast. If you measured this with coax cable connected leave it as is, some ringing on waveform wont hurt, eventually reduce Rd to 680 ohm.

[mohandes]

hi
i see pis of dear Tepco , and this pic of my coil : 28cm , 460mkh and 2.1ohm (without coaxial cable ) and damping R is 820ohm

[mohandes]

Here is a virtual comparison of using a diode and not having one. I see some apparent difference between the two circuits' performance, but how or if that equates to improved target detection can only be determined in the field .

It looks to me like adding the diode will cause flyback to decay much faster in the first few microseconds. If adding a diode works out for builders being able to sample earlier than they could have otherwise, that is a good thing. And if you can use a higher damping resistance than before, that should also allow a stronger signal to be seen at the receiver input.

I don't think the diode would need to have a 1500V breakdown voltage (although for all I know, the STTH1210 might still be the best choice for some reason or another), but it would be a bad idea to use something with a lower breakdown voltage as compared to the zener voltage of whatever MOSFET is being used.

In case it is not obvious, what I did with the progression in the photo was start with the "big" picture, and then zoom in sequentially towards the last few microseconds of the flyback's settling. Note that the 176us point is about 14us after the end of the transmit pulse.

hi
dear friend i use 450ohm for damping res and my coil near 460mkh and 2.2ohm ( plus coaxial cable near 3.5ohm )for 28cm coil. and this value is best result for my DP.
i test with 680 , 750 and ...1.2k but best result in 450ohm in AIR testing.
i can not find stth1210D in my country so i buy stth12R06D , Do you thing it is work or burn ?
and in finally , Diode help for faster respond and i think can better for Depth , i say OK ?or better say diode cause DP work better ?
can you simulation with my value i say you above and post here.i want know 450 ohm ok or 680 ohm.
regards

[calebsone]

I think I get it thanks porkluvr so with whatever coil,cable,and winding inductance and capacitances KT used needed the 680ohm and whatever my set up equals is how I need to set my dampening am I close to right? Or way off with how I understood what you said? And the easiest way to find that is through a pot to adjust till I find the right resistance for my coil set up

[green]

Recorded more data. No diode vs MUR460. Didn't get what I expected. Thought the amplitudes would be the same at longer delay times. The no diode recordings are higher. Using pi*L uh*circuit resonance Mhz(no R damp) to calculate R damp. No diode=303 ohms, MUR460=1100 ohms. I used 286 and 1000, a little over damped. I already had a 1k resistor for R damp, paralleled 1k with 400 for 286 ohms The diode in series reduces the current at turn off, might be the cause for lower amplitude. Used a 6 volt supply, 12 volt supply might have less difference. Any other thoughts would be appreciated.

[porkluvr]

So I know this is off current topic of the thread but by tune on the 680ohm resistor and the 560ohm do you mean exact to that number or find something close for the coil resistance and meter type. Or is it the number or nothing I'm all most done just needed this last bit.

Just so long as you are in the ballpark with the damping resistor you should be OK. If you don't have a scope, proper selection can only be trial and error - unless you already have a tested and true coil formulation procedure.

Even if you do have a scope, it takes a little bit of know-how to be able to interpret the results to know which way to go.

Tepco wrote a post not too long ago that has some nice photos and a good description.

Understand that coil resistance and inductance are not the only factors that affect your proper choice of a damping resistor. You also need to control the various capacitances of the coil windings, the cable, and MOSFET (hmmm, where did I see that before).

Here is a link to Tepco's post.


NOW it's time to go

[porkluvr]

Here are some models and symbols that might come in handy for somebody wanting to play with the DP tx timer. I won't post my circuit, but it should be easy enough to reproduce for somebody who gives it half a try. Of course you'll need to have LTspice (or some other other compatible spice application) installed on your computer.

Even though LTspice comes with an LM555 symbol, mine is modified from the original, and I've included it here. Nothing is wrong with the original symbol, but mine has more information.

Find the LTspice\lib\sub folder and put the .sub files there.

My standard.dio file has more diode models than the original. Find the cmp folder. Either simply replace the original standard.dio file with mine, or you can open it with a text editor and extract the STTH1210 model or whatever else you want, and then paste into your standard.dio file.

Make a new folder in the ltspice/lib/sym folder. I call mine "3rd party" and I have nested subfolders for MOSFETs, COMPARATORS, opamps, miscellaneous, and etc.

Place IRF740 symbol somewhere in the sym folder. Perhaps like so: LTspice/lib/sym/3rd party/MOSFET/IRF740.asy. Put the potentiometer symbol wherever you want. If you don't know how to use it, you'll figure it out. or ask for help.

You can drag and drop any symbol file (.asy) into an open LTspice window for editing, or maybe if you are just curious to see what makes it tick. CTL-A brings up an attribute editor window. See how I've construct 3rd party symbols so that when they are inserted into a simulation LTspice will locate and use the appropriate model file automatically (usually a .sub or a .mod file).

When you restart LTspice, the symbols should be available by clicking the icon that looks like an "and gate".

Whew, it's been a long day. I've gotta go.

[green]

Recorded some data. No diode, MUR460. 1N4937, 1N4004. The data was recorded with R damping disconnected. 280uh coil, the diode was connected in series with a IRF740 fet. No coil and 1N4004 had a resonance around 340khz, Mur460 and 1N4937 doides had a resonance around 1.25Mhz. The top traces had the scope probe connected to the coil. The bottom traces had the scope probe disconnected laying near the IRF740. Planning on recording amplifier out with no diode and a MUR460 diode with the coil critically damped to see how much faster the signal could be sampled. Those are the only high voltage diodes I have.